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antibiotic

Certain medicinal substances have the power to destroy or check the growth of infectious organisms in the body. The organisms can be bacteria, viruses, fungi, or the minuscule animals called protozoa. A particular group of these agents is made up of drugs called antibiotics, from the Greek anti (“against”) and bios (“life”). Some antibiotics are produced from living organisms such as bacteria, fungi, and molds. Others are wholly or in part synthetic—that is, produced artificially. Penicillin is perhaps the best known antibiotic. Its discovery and later development has enabled the medical profession to treat effectively many infectious diseases, including some that were once life-threatening. Antibiotics have revolutionized the treatment of bacterial infections in humans and other animals. They are, however, ineffective against viruses.

Penicillium mold is grown in a lab. The mold is the source of penicillin, one of the first and most…

Catolla—iStock/Thinkstock

Learn about antibiotics.

The general relationship between an antibiotic and an infectious organism is one of antibiosis. This word refers to an association of two organisms in which one is harmed or killed by the other. The relationship between human beings and disease-causing germs is one of antibiosis. If a person is affected by germs, he is the injured organism; if the germ attack is repelled by the body’s defenses, the germs are the injured organisms. When a

person’s defense system cannot control antibiosis in its own favor, antibiotics are used to tip the balance toward health. Homeostasis

The body’s balance between health and illness is called homeostasis. This largely depends on the relationship of the body to the bacteria with which it lives. For example, bacteria are always present on human skin. When the skin is cut, the bacteria are able to get inside the body and may cause infection. Usually the invading bacteria are destroyed by blood cells called phagocytes and by various actions of the immune system. When there are too many bacteria for the system to handle, or the infected person has a low resistance to infection, illness results and antibiotics are needed to help restore homeostasis. Action of Antibiotics

Antibiotics can be bacteriostatic (bacteria stopped from multiplying) or bactericidal (bacteria killed). To perform either of these functions, antibiotics must be brought into contact with the bacteria.

It is believed that antibiotics interfere with the surface of bacteria cells, causing a change in their ability to reproduce. Testing the action of an antibiotic in the laboratory shows how much exposure to the drug is necessary to halt reproduction or to kill the bacteria. Although a large amount of an antibiotic taken at one time might kill the bacteria causing an illness, such a dose usually would make the person suffer from illness caused by the drug. Therefore, antibiotics are given in a series of smaller amounts. This assures that the bacteria are either killed or reduced enough in numbers so that the body can repel them. When too little antibiotic is taken, bacteria can often develop methods to protect themselves against it. The next time the antibiotic is needed against these bacteria, it will not be effective. Administering Antibiotics

Learn why antibiotics are important and how to prevent their overuse.

To work against infecting organisms, an antibiotic can be applied externally, such as to a cut on the skin’s surface, or internally, reaching the bloodstream within the body. Antibiotics are made in several forms and given in different ways.

Topical. Topical application means “to a local area” such as on the skin, in the eyes, or on the mucous membrane. Antibiotics for topical use are available in the form of powders, ointments, or creams.

Oral. Tablets, liquids, and capsules are swallowed. The antibiotic is released in the small intestine to be absorbed into the bloodstream. Troches, or lozenges, are allowed to dissolve in the mouth, where the antibiotic is absorbed through the mucous membrane.

Parenteral. Applications outside the intestine are called parenteral. One form is an injection, which can be subcutaneous (under the skin), intramuscular (into a muscle), or intravenous (into a vein). Parenteral administration of an antibiotic is used when a physician requires a strong, quick concentration of the antibiotic in the bloodstream. Manufacture

Natural. At one time all antibiotics were made from living organisms. This process, known as biosynthesis, is still used in the manufacture of some antibiotics. It is actually the organisms that manufacture the antibiotic. The people involved merely provide favorable conditions for the organisms to do the work and then they collect the drug. For example, mold organisms are placed in a medium (a substance used for the growth of microorganisms) such as corn steep liquor to which milk sugar has been added. This forms a broth that is put into a tank, which is kept at a temperature of 25 °C (77 °F) and shaken for more than 100 hours. The mold organisms grow rapidly in this warm soup, producing penicillin as they do so. The penicillin is later extracted.

Synthetic. All penicillin types have an identical chemical nucleus called a ring. The chemical chain that is attached to the ring is different in each type. By changing the molecules of the chain, scientists devise drugs with potentially different effects on different organisms. Some of these drugs are useful in treating infections, some are not.

Pharmaceutical manufacturers now use computer-generated images of the rings and experiment with an endless variety of possible chains. Researchers have developed antibiotics with long half-lives (period of effectiveness), which allow taking the medication once in 24 hours instead of every few hours. The newer antibiotics are also more effective against a wider range of infections than were earlier drugs. Varieties

There are dozens of antibiotics. The following are in common use:

Penicillins. The various types of penicillins make up a large group of antibacterial antibiotics of which only those from benzyl penicillin are naturally produced from molds. Penicillin G and ampicillin are in this class. Another penicillin, called piperacillin, has been shown to be effective against 92 percent of infections without causing serious side effects. Penicillins are often given in combination with some of the following categories of drugs.

Cephalosporins. Similar to the penicillins, cephalosporins are often given when a sensitivity (allergic reaction) to the former is known or suspected in a patient. Cefotaxime sodium is a kind of cephalosporin that is very effective in combating deep infections such as those that occur in bones and those resulting from surgery.

Aminoglycoside. Aminoglycosides include streptomycin and neomycin. These drugs are used to treat tuberculosis, bubonic plague, and other infections. Because of potentially serious side effects, such as interference with hearing and their ability to make one sensitive to sunlight, these drugs are given with caution. (All antibiotics are given with care; caution implies more than usual possible negative consequences of drug administration.)

Tetracyclines. Tetracyclines are effective against pneumonia, typhus, and other bacteria-caused illness but can harm the function of the liver and kidneys. Tetracycline in a special gel base is used to treat many eye infections.

Macrolides. Macrolides are often used in patients who appear to be sensitive to penicillin. Erythromycin is the best known medicine in this group.

Polypeptides. The class of antibiotics called polypeptides is quite toxic (poisonous) and is used mostly on the surface of the skin (topically). Bacitracin is in this category. Sulfa Drugs

Sulfonamide was the first antimicrobial drug to be used. Sulfa drugs, which are made from chemicals, have largely the same effects as those of the later-developed penicillins. As sulfa drugs can have harmful effects on the kidneys—while being effective against kidney infections—they are always taken with large quantities of water to prevent the formation of drug crystals. Gantrisin is still among the most useful of these sulfa drugs. Other Antimicrobials

Other antimicrobials include furazolidone and tritethoprim. The first is used primarily in gastrointestinal infections; the latter, when combined with one of the sulfonamides, is effective in urinary and respiratory infections.

Antifungal. Antifungals combat illness caused by fungus such as candida. Fungus-caused infection requires long- term treatment. Drugs such as griseofulvin are often taken for six months. Most fungal infection occurs on the skin or the mucous membrane.

Antiviral. Very little is known about treating viral infections (the common cold is an example). A virus is thought to be the smallest infectious agent with the ability to replicate (reproduce) itself. Moreover, it seems able to mutate, or change, with great rapidity. The few drugs that are effective against viral infections interfere with the formation of new, normal cells and are therefore used with extreme caution. Other microbial drugs have little effect on a virus and are given only to treat bacterial infections that accompany or result from the primary viral infection. Resistance and Side Effects

An antibiotic acts by limiting or stopping (and therefore killing) the growth of a specific microorganism. It probably accomplishes this by interfering with the wall of the bacteria cell at which it is targeted while at the same time having little effect on the body’s normal cells.

When one is exposed continually to an antibiotic for an illness of long duration (such as rheumatic fever), the targeted bacteria may develop its own defense against the drug. An enzyme that can destroy the drug may be produced by the bacteria, or the cell wall can become resistant to being broken by the action of the antibiotic. When this happens, and it does most frequently in response to long or frequent treatment with penicillin or streptomycin, the patient is said to be “fast” against the drug. For example, one may be penicillin-fast, meaning penicillin is no longer able to help fight the infection and another type of antibiotic must be given.

Allergic reactions to antibiotics are usually seen as rashes on the skin, but severe anemia (too few red blood cells), stomach disorders, and deafness can occasionally result. It was once thought that allergic reactions to

antibiotics—penicillin in particular—were frequent and permanent. Recent studies suggest, however, that many people outgrow their sensitivity or never were allergic. The large number of antibiotics that are now available offers a choice of treatment that can, in most instances, avoid allergy-causing drugs.

It is well to remember that all drugs can cause both wanted and unwanted effects on the body. The unwanted ones are called side effects, and these must be balanced against the effects desired in determining if a particular drug will do more harm than good. It is a fact that all drugs have the potential to be both beneficial and harmful. Choosing the Appropriate Drug

Physicians can generally determine the type of organism responsible for causing the most frequently seen infections and know which class of antibiotic will be the most effective in combating it. Sometimes the agent causing the illness is not known. In this event a culture from the infection is examined under a microscope to identify the invading organism. The results of the laboratory work permit the physician to prescribe the most effective antibiotic against the specific disease-causing bacteria. History and Future

From such moldlike colonies came the first broad-spectrum antibiotic: clortetracycline, or…

Lederle Laboratories Division of American Cyanamid Company

The years between 1928 and 1940 were the most fruitful in the discovery and development of antimicrobial drugs. In 1928 Sir Alexander Fleming, a British bacteriologist, noticed that a mold growing in one of his laboratory cultures was able to destroy that culture’s bacteria. Since the mold that produced the substance that killed the bacteria was a species of Penicillium, he named the germ-killing substance penicillin. The first use of an antibiotic, however, is not known, as folk medicine has used various molds to fight infections throughout history. In 1935 a German chemist, Gerhard Domagk, discovered the first sulfa drug, prontosil. In 1941 penicillin was used to treat serious infections. The results were dramatic because patients who received the drug made

rapid and complete recoveries. Bacitracin, chlortetracycline, and streptomycin, naturally occurring antibiotics, were discovered by 1948. The penicillin ring was finally isolated in 1959 by British and United States scientists, and the way was open for the development of man-made, or engineered, antibiotics. The development of penicillin was the beginning of an era that has been called the golden age of chemotherapy. Since 1948, a large number of substances that inhibit or kill bacteria have been discovered.

Another use of antibiotics is as additives to the feed of animals. Chickens and beef cattle, for example, can be fed with these additives for better weight gains and to speed their growth.

Current work in antibiotics is largely in the area of viruses. Although some antivirals are available, most have toxic effects so severe that they can be used only in life-threatening diseases where the negative effects are the lesser danger. Preliminary studies, however, are reporting success in the development of safer antiviral drugs, and their use should be possible within the near future.

Ann Giudici Fettner

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human disease

A disease is a condition that impairs the proper function of the body or of one of its parts. All living things can succumb to disease. People, for example, are often infected by bacteria, but bacteria, in turn, can be infected by certain viruses.

Many people with kidney failure benefit from dialysis, an outpatient treatment in which the…

Hundreds of different diseases exist in nature, and every disease has a cause, though the causes of some remain to be discovered. Each disease has a particular set of symptoms and signs—clues that assist in diagnosis. A symptom is something a patient can detect, such as nausea, bleeding, or pain. A sign is something

that a doctor can observe in a patient. Furthermore, a sign can be quantified, or measured, while a symptom cannot. For example, chest pain is a symptom—its presence does not indicate its cause, and the pain itself cannot be measured. An abnormal heart rate, however, is a sign—it can be measured and otherwise evaluated by the physician. The results of this evaluation help determine the cause of the abnormal heart rate, which could be due to many different factors. (See alsodiagnosis.)

All diseases display a cycle consisting of the onset, or beginning of symptoms; the course, or time span of affliction; and the resolution, or end of the disease. This may occur when the disease and its signs and symptoms disappears via a cure or through the death of the patient. Some diseases, such as polio, are considered “resolved” even though the victim is left disabled (seepoliomyelitis). How Disease Is Classified

Students in Hong Kong wear surgical masks to protect themselves from SARS, a highly contagious…

Anat Givon/AP

Diseases can be classified in a number of ways, depending on the information needed by the doctor or scientist. One way to classify diseases is by the population groups they affect or the way they spread. This is called epidemiology, and it is a very important science. Public health officials use epidemiology to study and manage society’s response to disease.

An epidemiologist looks for several types of information about a disease. For example, he may ask if certain diseases appear mostly among children. If so, he may then recommend large-scale immunization programs, such as those used for the measles-mumps-rubella vaccine. Epidemiologists also look for associations between certain habits and diseases, such as the connection between smoking and lung disease.

Epidemiologists also try to predict how likely it is that one or more diseases will occur in an area where the population is affected by a common circumstance, such as untreated drinking water. These predictions are based on mathematical formulas that determine the chance, or probability, of an outcome given particular circumstances.

It should be no surprise that epidemiologists are also concerned with epidemic diseases—that is, diseases that strike many persons or entire populations within a relatively short period. History has seen many devastating epidemics, from the plague in Europe during the Middle Ages, to the influenza pandemic (global epidemic) of 1918–19, to the AIDS crisis currently gripping much of the world. When a disease stubbornly remains in the same region year after year, it is called an endemic disease. Yellow fever, for instance, is endemic to tropical South America and Africa, prompting many countries to require travelers to and from those regions to present proof of inoculation against the disease.

Diseases are generally defined as either acute or chronic. An acute disease has a quick onset; most run a relatively short course, during which symptoms may be mild or severe. The common cold is a relatively mild acute disease of fairly short duration. SARS, or severe acute respiratory syndrome, also has a quick onset; but unlike a cold, SARS can rapidly become very serious, even fatal. A chronic disease has a slow onset and a long duration that can last for years. Rheumatoid arthritis is an example of a chronic ailment with a very long course. Some diseases, such as bronchitis, have both acute and chronic forms.

One of the most important ways of classifying diseases is to distinguish between infectious and noninfectious diseases. Infectious diseases are caused by living organisms such as bacteria, fungi, protozoans, viruses, and parasites. Whatever the causative agent may be, it survives in the “host” person—in other words, it is infectious. If it can be passed on to another person, it is also communicable. Noninfectious diseases are not caused by a living organism; and because they are not passed from one person to another, they also are noncommunicable. Noninfectious diseases have a wide range of causes, such as substances in the environment (silicosis and black lung), diet deficiencies (rickets and scurvy), disorders of the body’s immune system (lupus), or inheritable genetic defects (Tay-Sachs disease).

Frequently, diseases are classified according to the organ or organ system that has been affected. There are diseases of the respiratory system (pneumonia), cardiovascular system (coronary artery disease), nervous system (multiple sclerosis), and endocrine system (diabetes mellitus), among many others.

Diseases and their associated signs and symptoms are further distinguished by the extent of their spread in the body. A local, or localized, ailment or symptom is confined to a particular site or single organ system, whereas a systemic disease affects the entire body. This is an important factor in treatment. For example, an infected cut may be treated with a topical antibiotic cream if the infection is limited to the site of the injury. If the infection invades deeper tissues and spreads to the bloodstream, the infectious organism can be carried to every organ in the body. To treat this, doctors must prescribe a systemic drug; this is usually an oral or injectable medication that can enter the bloodstream and fight the infection at all affected sites. Not all systemic diseases are infectious, however. Cancer and diabetes mellitus are two examples of noninfectious systemic diseases. Infectious Diseases

Humans live in a world where many other living things compete for food and places to breed. Some of these organisms—bacteria, for instance—live within the human body and contribute to bodily functions such as digestion. Ordinarily, the immune system keeps these microbes from causing damage.

Sometimes, however, harmful bacteria penetrate the body’s defenses. In other cases, organisms living harmlessly within the body become too numerous or acquire harmful characteristics. They then become pathogenic, or disease-causing, organisms (called pathogens or simply germs). The same is true for fungi, viruses, and parasites.

How Germs Invade the Body

Antibiotics, delivered from two small discs and a gradated strip, inhibit the growth of…

Dr. Richard Facklam/Centers for Disease Control and Prevention (CDC)

In some disease cycles, the pathogen is harbored inside a host that acts as a reservoir for…

Encyclopædia Britannica, Inc.

Pathogenic organisms can enter the body in various ways. Some, such as the virus that causes the common cold, are inhaled, while others, such as the bacterium that causes leprosy, enter through direct contact between human bodies. Many pathogens, such as those that cause gastroenteritis, or stomach flu, get into the body through contaminated food, water, or utensils. Certain pathogens are transmitted only through sexual activity with an infected individual.

Some germs may enter the body through the bite of an animal. Mosquitoes transmit West Nile virus and Plasmodium, the parasite that causes malaria. Typhus is caused by infection with rickettsial bacteria transmitted by lice. Lyme disease is spread through the bite of a tick, while rabies is transmitted via the bite of an infected mammal. Organisms that deliver an infectious agent to a host are called carriers. In many cases, carriers themselves do not become ill. For example, mosquitoes are unaffected by the parasites and viruses they carry. Other diseases, such as rabies, cause illness in carrier and host alike.

To acquire certain contagious diseases, a person need only be in the presence of someone who is already ill, or come in contact with infected bodily fluids such as blood or urine. Infectious diseases are called contagious if they can be passed between people. Anyone suffering the frank symptoms of a contagious disease can pass it on to others while the disease is running its course. However, some pathogens can be transmitted during the incubation period of a disease—the period between infection and the onset of symptoms. Some pathogens can be transmitted even when the initial victim is recovering from the disease. Like animals, some people can be asymptomatic carriers, carrying an infectious organism without ever falling ill.

Most infectious diseases are species-specific—that is, a disease such as parvovirus, which affects dogs, will not affect humans. However, a large number of diseases can strike both humans and animals and can be passed between them (though most commonly these are transmitted from animals to humans and not vice versa). These diseases are called zoonoses. Zoonotic diseases are a public health concern, though some are more serious than others. Ringworm, for example, is relatively mild and can be treated with antifungal drugs. Other zoonoses, such as rabies, avian influenza virus, and plague, are extremely serious and can lead to epidemics.

Once an infectious organism gains a foothold in the body, it begins to multiply. The length of the incubation period depends on the pathogen. Symptoms of the common cold appear within days, while those of kuru, a rare disease of the nervous system, can appear years after infection.

Several factors determine whether a person will fall ill after being infected. These include the number of invading germs, or the dose of the infection; the body’s ability to fight the disease; and the virulence of the pathogen. Virulence is a measure of a pathogen’s ability to do harm. Highly virulent pathogens, such as the Ebola virus, cause severe disease that progresses so rapidly that, in most cases, death results despite the best efforts of medical personnel.

Many pathogenic species include some strains that are highly virulent and others that are not. For example, all influenza strains have the potential to cause severe illness, though most of the strains seen each winter are low in virulence, causing a short course of unpleasant but controllable illness in most victims. The devastating influenza pandemic of 1918 was caused by a highly virulent flu strain that killed at least 20 million people around the world within one year. Low virulence should not be confused with harmlessness, however: even organisms with low virulence can cause serious illness if left untreated.

How Infections Are Fought

Macrophages, the principal phagocytic (cell-engulfing) components of the immune system, ingest and…

Encyclopædia Britannica, Inc.

As a first line of defense, a healthy body has a number of physical barriers against infection. The skin and mucous membranes covering the body and lining its cavities offer considerable resistance to invasion by

infectious organisms. If these barriers are injured or burned, however, resistance drops. In that case, the body calls up its second line of defense: the immune system. Circulating through the blood and lymph, white blood cells flock to infected areas and try to localize and suppress the infection. Some white blood cells, such as macrophages, engulf and digest the pathogens in a process known as phagocytosis.

Lymphocytes, another group of white blood cells, play a key role during this line of defense. Lymphocytes are divided into two main classes, or types: T cells and B cells. T cells use several methods to kill pathogens directly, in some cases tagging them with markers so that other cells can attack them. B cells manufacture and release protective proteins called antibodies, which are “custom-designed” by the B cells to target specific pathogens. Some B cells remain in the body for years after the pathogen has been eliminated. This creates a biological “memory,” giving the body a long-lasting immunity against future attacks by the same kind of invader. (See also immune system.)

Drug therapy

Since the advent of antibiotic therapy in the 20th century, a broad range of infection-fighting drugs has been developed to work in conjunction with the body’s immune system. The antibiotics penicillin and tetracycline, for instance, are very effective against some bacterial infections, such as gonorrhea and acne. However, antibiotics have no effect on infections caused by viruses, fungi, protozoa, or other parasites. Thus nonbacterial infectious diseases are treated with other classes of drugs. For example, some herpesvirus infections respond to the antiviral drug acyclovir. Herpesvirus does not respond to antibiotics, however, because the infection is not caused by bacteria. Similarly, antifungal drugs are used to treat fungal infections, antiprotozoal medicines treat diseases caused by infection with protozoa, and anthelmintics fight worm infestations such as trichinosis, which is caused by intestinal roundworms.

Drug resistance

Some individual microbes are naturally resistant to certain drugs. After repeated exposure to a drug, however, some nonresistant microbes may gain resistance by a chance mutation; others may acquire genes for resistance from a resistant bacterium. Over time these bacteria form a new drug-resistant strain, forcing doctors to prescribe multiple drugs to fight infections with these germs—which may later gain resistance to the new drugs.

Incorrect antibiotic use has led to a rise of drug-resistant pathogens, producing a global public health issue. Once-powerful drugs such as penicillin have become ineffective against new drug-resistant bacteria strains, such as those that cause tuberculosis and staphylococcal infections. As a result, the incidence of these once- controllable diseases is steadily increasing. (See alsoantibiotic.)

Vaccines

Many dangerous diseases have been controlled or eradicated (stamped out) through the use of vaccines. Some vaccines protect against viruses, such as measles; others guard against some bacterial infections, such as diphtheria, or toxins, such as tetanus. The once-widespread viral disease called smallpox was eradicated around the world in the 20th century, thanks to an international effort aimed at wide-scale vaccination. (See also smallpox; vaccine.)

Cardiovascular Diseases

These cross-sectional diagrams of human blood vessels show a normal, healthy artery on the left, and …

Encyclopædia Britannica, Inc.

Disease of the heart and/or the blood vessels, called cardiovascular disease, is the leading cause of death in most developed countries, particularly those of North America and Europe. It claims millions of lives every year around the world—more than a million per year in the United States and more than 70,000 in Canada.

Coronary Artery Disease

Disease of the coronary arteries that supply oxygen and nutrients to the heart is the most common heart ailment. Coronary artery disease accounts for more than a third of all deaths among males in the United States between the ages of 35 and 55. It also strikes many women past the age of 50. Hypertension (high blood pressure), overweight, cigarette smoking, diabetes mellitus, excess cholesterol, triglycerides and other fats in the blood, and lack of regular exercise contribute to the chance of developing this disease.

This micrograph shows a cross-section of a coronary artery narrowed by artherosclerotic plaque…

National Heart, Lung, and Blood Institute (NHLBI)

Coronary artery disease is characterized by formation of one or more atheromas. These are fatty deposits of cholesterol that form beneath the inner lining of the artery and obstruct the passage of blood needed to nourish the heart muscle. This also sets up conditions for a blood clot in the coronary artery (seeblood). Atheroma formation seems to run in families. However, eating foods rich in saturated animal fat and cholesterol are also contributing factors.

Many persons with coronary artery disease do not experience any symptoms. However, if the obstruction is bad enough, it may cause angina pectoris, myocardial infarction (heart attack), or heart enlargement and failure.

Angina pectoris is a severe, squeezing chest pain that occurs when the coronary blockage prevents adequate oxygen from reaching the heart, especially during periods of exertion. Rest and medication often relieve the pain. Unlike a heart attack, angina is a temporary condition, and heart muscle is not destroyed.

Myocardial infarction is the medical term for a heart attack. When the coronary artery becomes so obstructed that the myocardium, or heart muscle, does not receive oxygen, the muscle tissue dies, or becomes infarcted. For many years doctors believed that the infarction was caused by a blood clot blocking the coronary artery. However, later studies revealed that most clots form in the artery after the infarction.

The first hours after a heart attack are critical because abnormal heart rhythms, or arrhythmias, may develop. Without swift medical intervention, death follows in three or four minutes after an attack. Patients are usually treated in the coronary care unit of a hospital for a few days to enable electronic monitoring of the heart rate and rhythm (seehospital).

Repeated heart attacks can strain the remaining healthy heart muscle, leading to heart failure. As attacks destroy more and more heart muscle, the remaining muscle enlarges to compensate. Increased pressure in the weakened heart causes fluid to back up into the lungs. As a result, the heart output—that is, the volume of blood pumped out with each contraction—cannot keep pace with the body’s oxygen demands. (See alsoheart.)

Heart Rhythm and Pacemakers

A node of special cells in the heart controls its rhythm by regularly producing energizing electrical signals. Sometimes, abnormal signals cause extra heartbeats, or tachycardia. At other times, especially in older persons, the signals might be conducted poorly, thus slowing the rate of beating. When a person’s heart rate drops below 40 beats a minute, he usually feels faint and cannot function well. In that case, he often can be fitted with an artificially powered heart pacemaker.

Rheumatic Heart Disease

Rheumatic heart disease has both an acute form and a chronic form. The acute form, rheumatic fever, inflames joints and heart muscle. Although the joints recover, if the condition becomes chronic the heart valves may become scarred. Rheumatic fever most often affects the mitral, or bicuspid, valve of the heart, producing a blockage called mitral stenosis.

Rheumatic fever is caused by an overactive immune response to infection with a strain of beta-hemolytic streptococcal bacteria, which causes strep throat and scarlet fever. Unlike most pathogens, the cell wall of beta- hemolytic Streptococcus includes a protein that is also found in human heart muscle. When a person with strep throat or scarlet fever develops antibodies against the bacterial protein, the same antibodies may also attack that person’s own heart muscle. The antibodies continue to damage the muscle over many years. This scenario is typical of an autoimmune response, a process in which the immune system attacks the host’s own tissues (see “Autoimmune Diseases” in this article).

Penicillin and other antibiotics treat the initial streptococcal infection; in some cases, timely treatment can prevent heart damage. In severe cases, however, surgery might be needed after many years to repair or even replace a damaged heart valve.

Hypertensive Heart Disease

Hypertension, or high blood pressure, is a fairly common disorder. Ordinarily, the pumping action of the heart creates sufficient pressure to move blood throughout the body. Increased resistance to blood flow from the arteries causes the blood pressure to rise above normal. Because the heart must then work harder to maintain the higher pressure, it enlarges.

Blood pressure is regulated by a complex interaction between the heart, the nervous system, and the hormone renin, which is produced in the kidneys. Some persons with hypertension have too much renin in their blood. In other individuals, lifestyle issues such as diet and stress play a role in developing the disease. High blood pressure increases the wear and tear on blood vessels and can cause heart failure, strokes, and kidney disorders. If detected early, however, it can be treated with drugs.

Congenital and Inflammatory Heart Disease

If the heart does not form properly during fetal development, this will result in a child born with a congenital heart defect. There are numerous types of congenital heart problems: the heart’s valves might be too narrow or missing altogether, or the septum—a wall separating the heart chambers—might be incomplete, leaving a hole between the heart chambers. Some congenital problems correct themselves as the child grows; others must be surgically repaired.

Some substances are dangerous to the heart. Excessive alcohol drinking weakens and enlarges the heart. The heart tissues are vulnerable to infection by microbes and parasites, as well as infiltration by toxins and other agents. Inflammation of the heart muscle (myocarditis), pericardium (pericarditis), inner lining (endocarditis), valves, and related tissues is always serious and requires swift medical intervention and intensive care. Persons with faulty valves or congenital heart disease are susceptible to bacterial endocarditis.

Blood Vessel Disorders

Atherosclerosis, the thickening and hardening of arterial walls, may occur in many arteries. Cholesterol and other fats that form in the process obstruct the affected arteries and, at times, produce a thrombus, or clot, in them. Sometimes, these clots break away, especially from the heart, and embolize, or travel to some other part of the circulatory system, where they can block a blood vessel and prevent oxygen from reaching tissues.

A brainembolism can cause the cardiovascular accident known as stroke. A stroke occurs when bloodflow to the brain tissues is blocked, depriving the brain tissue of oxygen and destroying key nerve cells. A blood clot in one of the brain’s blood vessels, a hemorrhage from a broken blood vessel in the brain, the hardening of a brain artery—any of these conditions may result in a stroke. Depending upon the brain area affected, a stroke can culminate in loss of limb use—particularly the arms—speech difficulties, and partial blindness. Some strokes are minor; with time and treatment, many victims regain most or all of the impaired body functions. In severe cases, extensive physical or speech therapy is needed for rehabilitation; the degree of recovery for these patients varies.

The vascular disorder called aneurysm occurs when the walls of a large artery weaken and balloon out. Small aneurysms may not be critical, but large aneurysms can rupture. If the ruptured vessel is a major one, such as the aorta, or is located in the brain, death can follow quickly unless the patient undergoes emergency surgery. A wide range of conditions, from atherosclerosis to syphilis, can promote aneurysm development.

Varicose veins, bulging veins in the leg, develop when the walls of the veins weaken. The condition may be inherited or may stem from phlebitis, an inflammation of the veins. Phlebitis may trigger clots in the veins, which

sometimes break away, travel to the lungs, and form a pulmonary embolus. Drugs used to prolong clotting time often correct the disorder (seeblood). Respiratory System Diseases

A girl uses an inhaler to deliver medication for asthma to the respiratory system.

The lungsare spongy organs through which vital oxygen enters the body and needless carbon dioxide exits. Oxygen and carbon dioxide are exchanged in and out of capillaries in the many tiny air sacs, or alveoli, in the lungs. Although they are susceptible to disease, the breathing passages—the nose, throat, trachea, and bronchi—are lined with mucous membranes that form an initial line of defense against pathogens and irritants ( seelung). The lungs, however, are highly vulnerable to invading organisms and irritants and can become seriously diseased. Lung diseases are also referred to as pulmonary diseases.

Upper Respiratory Diseases

Although they are lined with membranes that offer initial defense against pathogens, the nose, throat, and other breathing passages are vulnerable to infection by bacteria or viruses. Untreated or long-term infection of the bronchi and bronchioles can result in chronic bronchitis. It is marked by cough and increased production of sputum, an accumulation of saliva, mucus, and pus. Air pollution and cigarette smoking both can aggravate the condition. Frequent bouts of chronic bronchitis can permanently scar the airways, critically impairing their protective lining. Persons who suffer from chronic bronchitis are vulnerable to developing pneumonia and other infectious diseases of the lower respiratory system.

Infectious Lower Respiratory Diseases Pneumonia

Pneumonia, or acute infection or inflammation of the lungs, may occur suddenly in a seemingly healthy person. It is usually marked by fever, cough, and chest pain. X rays of the lungs show patches of inflammation. Viral pneumonia, though serious, is generally self-limiting. Both bacterial and fungal pneumonia, however, can be quite serious, depending upon the infecting pathogen. Drug therapy, particularly a vaccine against pneumococcal bacteria—a group that causes especially serious disease in the elderly and in children—has proved vital in fighting bacterial pneumonia.

Inflammatory diseases

Pleurisy is another disease affecting the lower respiratory system. It is caused by inflammation of the pleura, the double membranes that surround each lung and line the chest cavity. Pleurisy can occur as a complication of pneumonia or may result from direct infection of the pleura.

Inflammation of the muscle surrounding the airways results in the chronic disease called asthma. Signs include wheezing or whistling sounds accompanying each breath. Many cases arise in connection with chronic bronchitis or respiratory allergies; however, exposure over long periods to almost any airborne irritant results in asthma. Most cases are treated with inhalable drugs that reduce the inflammation and relax the bronchiolar muscle. Serious cases may require oral corticosteroids.

Fungal diseases

Fungal invasion of the lungs produces symptoms that resemble influenza or pneumonia. Fungal pulmonary disease can range from mildly serious to life-threatening. After invading the lungs, some fungi may disseminate, or spread, to other organs, including the heart and the meninges (the tissue covering the brain and spinal cord). Systemic fungal diseases are among the most difficult infectious diseases to treat, and often require hospitalization and intravenous administration of powerful drugs. Among the most serious fungal pulmonary diseases are histoplasmosis, blastomycosis, aspergillosis, coccidioidomycosis, and Candida pneumonia.

Lung abscess

Development of a lung abscess is possible with any infectious respiratory disease, though many such abscesses are associated with periodontal, or gum, disease. In these cases, bacteria associated with the latter are inhaled into the lungs, where they colonize the tissue, eventually forming an abscess—an accumulation of pus inside a cyst-like mass. If the abscess ruptures, or bursts, pus is spread into the surrounding tissue, and may enter the bloodstream. The ruptured abscess leaves behind a cavity inside the lung tissue. A lung abscess not only damages the lung itself, but it also can spread infection to other parts of the body.

Tuberculosis

One of the most serious diseases in humans is tuberculosis (TB), a complex disease that most often strikes the lungs. It is caused by the bacterium Mycobacterium tuberculosis and is transmitted from person to person through the air. In the lung the bacteria establish colonies; these attract a large immune response that produces granulomas—solid masses of immune cells that trap and destroy the bacteria. Granulomas remain dormant in the lungs for years; however, they can reactivate, triggering a fresh immune reaction that destroys the granulomas themselves and leaves cavities, or holes, in the lung. The tissue destruction from TB seriously impairs lung function producing cough, chest pain, fever, blood in the sputum, and weight loss.

TB is generally treated with the oral antibiotics isoniazid and rifampin. To effectively defeat the disease, however, the drugs must be taken by the patient for almost one year. Inadequate treatment of TB—for example, among patients who do not complete the entire course of drug therapy—leads to the development of drug resistance among the bacteria remaining in the lungs. These newly resistant bacteria multiply and spread to other individuals, setting up conditions for outbreaks against which traditional antibiotics are ineffective.

Before the advent of drug therapy in the 20th century, TB—historically called consumption—was a leading public health problem, particularly among poor people living in overcrowded and unsanitary conditions. Antibiotics radically changed the course of the disease; within decades outbreaks were less common and prevalence greatly decreased. However, lack of compliance by patients to complete the entire course of therapy later led to

rebounding of the disease and an alarming rise in drug resistance. By the late 20th century, the global incidence of tuberculosis—once one of the most remarkable triumphs of antibiotic therapy in public health medicine—was steadily increasing due to the rise of multi–drug-resistant strains.

Noninfectious Respiratory Diseases Emphysema

Emphysema is a serious lung disease that follows destruction of the elastic and connective tissue fibers supporting the lung. It is linked with advancing age, though certain forms of emphysema are inherited. Heavy cigarette smoking and long exposure to air pollutants seem to encourage the disease. A person with emphysema, lacking sufficient lung elasticity, wheezes and has trouble breathing. Furthermore, air movement in the lungs is reduced and the patient is easily fatigued because he fails to get enough oxygen or get rid of enough carbon dioxide.

Pulmonary edema

Because of their physiologic relationship, the heart and the respiratory system often are linked in disease. Acute pulmonary edema results when fluid quickly accumulates in the lungs and fills the alveoli. The fluid buildup is caused by heart trouble that, in turn, produces back pressure in the pulmonary veins and the left atrium of the heart to which they carry oxygen-rich blood from the lungs. A person suffering acute pulmonary edema suddenly becomes breathless and turns blue because of oxygen-poor blood. The condition is treated with oxygen, digitalis to strengthen heart action, and diuretics to speed fluid removal by the kidneys.

Occupational lung diseases

Miners and some industrial workers are extremely vulnerable to developing respiratory disease because of the conditions in which they work. Pneumoconiosis, which means “dust disease,” is the name given to this family of disorders. Silicosis results from inhaling quartz dust; asbestosis is found among workers exposed to asbestos dust. Inhalation of coal and quartz dust leads to the development of anthracosilicosis, sometimes called black lung disease. Textile mill workers are vulnerable to developing byssinosis, also known as brown lung disease. It results from long-term exposure via inhalation of cotton and other fibers found in textile mills. In general, workers who develop these diseases are prone to later complications such as heart failure, emphysema, and cancer.

Respiratory distress syndrome

Formerly called hyaline membrane disease, respiratory distress syndrome is an often-fatal disorder of some prematurely born infants. A protein material lines the alveoli of the lungs in afflicted babies, limiting the amount of oxygen their blood can receive. Cancer

Uncontrolled division and a chaotic appearance are hallmarks of cancer cells. Normal cells (left)…

Courtesy National Cancer Institute

The word cancer refers collectively to more than 100 different diseases, all characterized by the rampant and abnormal growth and spread of cells. It is the second leading cause of death in most developed countries and claims millions of lives worldwide each year. Cancer can affect almost every type of tissue in the body. Many forms of cancer occur in a solid tissue or organ, where the rapidly multiplying cells form one or more masses, or tumors. Some cancers do not form tumors, however, and are manifested as malignant (abnormal and rapidly growing) cells that circulate in the blood or lymph.

Cancer is categorized according to the tissue type in which it develops. Cancer that arises in muscle, bone, connective tissue, blood vessels, and fatty tissue is called a sarcoma. Cancers found in cells that line the body’s cavities and organs, and in some skin cells, are classified as carcinomas. Cancer types are named and further classified by the specific location where they arise. Leukemia is so named because it is an abnormal proliferation of white blood cells, which are sometimes called leukocytes (from the Greek leuk-, meaning white, and -cyte, meaning cell). Cancer of the bone is called osteosarcoma (the prefix osteo- is from the Greek word for bone). Basal cell carcinoma, the most common type of cancer in the world, is a form of skin cancer (basal cells are part of the skin).

Cancer can strike any part of the body. Some cancerous tumors are especially fast growing and can double their size within a month or so. Others are slow growing and may not spread for many months or even years. If cancer develops within a vital organ or tissue, such as the lung or liver, normal function will be impaired, with possibly fatal results.

Globally, breast cancer is the leading form of cancer in women and a leading cause of cancer-related deaths in many countries. In the United States, it is second only to lung cancer in claiming the lives of female cancer patients. The prevalence of cervical cancer in the United States has decreased dramatically thanks to the Pap test, one of the most successful cancer screening methods developed (seecancer, “Breast and Uterine Cervix”). Globally, however, cervical cancer remains the second most important cancer in women.

Cancer of the prostate gland is the leading form of cancer among men in the United States, though lung cancer accounts for more deaths. Lung cancer is the most important form of cancer, both in prevalence and mortality, among men worldwide. (See alsocancer.) Skin Diseases

Because of its exposure, the skin is perhaps more susceptible to disease than any other organ. Composed of several thick layers of specialized cells, the skin forms a tough barrier that prevents foreign substances, both biologic and chemical, from entering the body. The skin itself is part of the first line of immune defense, serving as a barrier to invasion by toxins and microbes. Any break in the skin, as from a cut or scrape, gives foreign material an opportunity to sneak into the body’s interior.

The skin is richly supplied with sweat glands, nerves, and blood vessels (seeskin). If the body’s temperature rises, the sweat glands perspire, producing a fluid composed mostly of water and salts. As this evaporates on the skin surface, it cools the skin, thus helping the body to remain at a constant normal temperature. In cases of anhidrosis—a condition in which the body cannot perspire—body temperature can rise to dangerous levels. Anhidrosis can occur as a result of injury to large portions of the skin. It is also a serious complication of heatstroke.

The skin contains many oil glands, which lie adjacent to hair follicles. The glands produce oil, or sebum, which helps lubricate the skin. When sebum is overproduced it accumulates in the hair follicles, attracting bacteria from the normal skin flora. This combination of sebum and bacteria produces whiteheads, blackheads, and pimples. Whiteheads are a mix of bacteria and oil that form whitish bumps just below the skin’s surface. Pimples contain the same materials but are also inflamed. Dead skin cells accumulate in the hair follicles, producing blackheads, whose characteristic dark color comes from melanin, the pigment responsible for skin color.

Acne is an outcropping of all three types of blemishes. It is typically seen in adolescence and may be related to the hormonal changes that accompany sexual maturity. Acne is not caused by food, emotions, or uncleanliness. Antibiotics are used to treat severe acne, but most cases respond well to local application of special lotions or creams that dry the blemishes, allowing them to peel away. (See alsoacne.)

Warts are rough, benign (non-cancerous) growths of the top skin layer caused by infection with the human papillomavirus (HPV). Warts may occur on any body surface and are spread from person to person through direct contact. HPV transmitted via sexual activity produces genital warts. There is no single effective treatment for warts; depending upon the number of warts, their location, and the patient’s age, the growths may be removed with chemicals that “burn” the wart away. Other treatments include the use of liquid nitrogen to freeze the wart (which then crumbles away), or excision by laser or simple surgery. Despite treatment, some warts may later reappear.

Hives, or urticaria, are acute, itchy, whitish elevations of the skin. Hives usually result from an allergic reaction to foods or medicines. Antihistamine drugs, both oral and topical, offer some relief for mild bouts. Severe cases of hives can be treated with a series of desensitizing shots (seeallergy).

Eczema, or dermatitis, is a superficial inflammation of the skin. It can result from an allergic reaction to poison ivy, dyes, or drugs. Such irritants as acids, solvents, or excessive use of soap or detergents also can provoke an outbreak, as can sunburn. Some forms of eczema, such as infantile eczema and seborrheic dermatitis, stem from unknown causes. However, nearly all types of eczema can be relieved by the application of corticosteroid creams.

Like all body systems, the skin is prone to infection. Athlete’s foot is a common fungal infection of the skin between the toes. The infected area is scaly, moist, and itchy. It usually has a disagreeable smell. Athlete’s foot can be relieved with daily application of topical antifungal drugs such as griseofulvin. In most parasitic infections, such as scabies or lice infestation, parasites burrow under the skin to lay eggs, producing intense inflammation characterized by severe itching and reddened patches of skin. Bacteria can produce mild to severe infections, depending upon the infecting strain and the extent of the infection. Several types of bacteria produce the serious condition called necrotizing fasciitis. One form of this, caused by an aggressive strain of Streptococcus, is called the flesh-eating disease, because the infection travels so rapidly and destroys so much tissue that amputation is sometimes required. Without treatment, the patient becomes toxic and goes into shock within days. Even with surgical intervention, death rapidly follows in many of these cases. Nervous System Diseases

The nervous system is the rapid communication system of the body. Information from the outside world enters the body through the sense organs and is sent to the spinal cord for instant response or is relayed to the brain for further processing. (See alsonervous system; brain and spinal cord.)

Nerves and the membranes that protect portions of the nervous system are susceptible to breakdown or infection. The microorganisms that cause such diseases as mumps or infectious hepatitis can infect the nervous system, too.

Nervous System Infections

Meningitis is an inflammation of the meninges, or membranes around the brain and spinal cord. The disease commonly results through infection with microbes, such as viruses and bacteria. Some cases develop without infection; reactions to certain drugs or noninfectious brain diseases may produce meningitis. Viral meningitis is the most common form of the disease. Although serious and mildly contagious, it usually runs a short course from which most people recover completely. More severe is bacterial meningitis, which requires immediate medical attention and can be fatal if not treated aggressively. A common sign of meningitis, in addition to fever, is the presence of a stiff neck.

Shingles, or herpes zoster, is an inflammation of certain nerve tissues. Painful skin bumps occur over the line of the inflamed nerve or its branches. Shingles and chicken pox are both caused by the same virus.

Noninfectious Nerve Disorders Neuritis and neuralgia

Neuritis is an inflammatory condition caused by the degeneration of one or more nerves. It is often marked by a pins-and-needles feeling, a burning sensation, or a stabbing pain. Neuritis can result from infection, especially of the facial nerve, hard body blows, or bone fracture causing nerve injury. Repetitive movements, such as using a computer mouse, can also trigger neuritis.

Neuralgia is often confused with neuritis but it is a distinct problem. Neuralgia is characterized by sudden, sharp bursts of pain along any of the sensory nerves near the body surface. Trigeminal neuralgia is a disorder of the trigeminal nerve, or fifth cranial nerve, whose branches are distributed along the cheek and to the eye, nose, jaw, and mouth areas (seenervous system). Attacks occur suddenly and last for several seconds, during which a severe, stabbing pain shoots across the side of the face.

Inflammation

Inflammation of nerves generally produce localized symptoms, though in some cases pain can be “referred.” For example, an inflamed nerve in the hip can produce pain in the knee. Sciatica is a disorder characterized by severe leg pain resulting from an inflamed sciatic nerve, which extends down the back of the leg. Sciatica is usually caused by a ruptured, or “slipped,” disk—one of the pads between the spinal vertebrae of the spine— that presses on the nerve’s root near the spine.

Vertigo

The inner ear regulates equilibrium. Loss of equilibrium is called dizziness or vertigo.

Contunico © ZDF Enterprises GmbH, Mainz

Some nerve disorders result from problems in the sense organs. Vertigo is a dizziness or disorientation in which the sufferer feels as though he is falling through space. It results from problems with the body’s balancing system, part of which is located in the inner ear (seeear).

Parkinson’s disease

Parkinsonism, or Parkinson’s disease, is a chronic disease that stems from decreased production of the neurotransmitter dopamine, which is produced in the brain. The reason for this remains unclear despite intensive research. People with Parkinson’s experience episodes when mobility is limited; they may move with a slow, shuffling gait, have decreased facial expressivity, and experience muscle tremors, or shakes. They also have trouble speaking and swallowing. Parkinson’s is a progressive disease, which means that its symptoms worsen with time. There is no cure for Parkinson’s; however, the disease may be treated with a drug called levodopa, or L-dopa, which is converted into dopamine in the brain. Several other drugs may offer modest relief of some symptoms. Physical, occupational, and speech therapy are also helpful to patients. Surgical treatment is also used in some cases.

Multiple sclerosis

Multiple sclerosis (MS) is a chronic, degenerative disease of the central nervous system. In MS, the fatty myelin sheath that surrounds the nerves is progressively destroyed, thus interfering with proper nerve-signal transmission to muscles and organs (seenervous system). MS develops slowly but eventually involves the entire brain and spinal cord. Muscle control, vision, mental abilities, and many other body functions are eventually impaired.

Most experts agree that MS is an autoimmune disease. However, the precise trigger for the onset of MS remains unclear, and there is no cure. Treatment is geared toward relieving symptoms, reducing inflammation, and regulating the immune system. Some forms of the disease are relatively mild; with treatment, these patients may be able to pursue normal, though modified, activities. In other forms, however, the disease progresses rapidly, producing severe debilitation.

Epilepsy

Epilepsy is a brain disorder in which nerve signals “fire” abnormally and cause convulsive seizures, or alternating muscle contractions and relaxations. Scar tissue in the brain can provoke some seizures. In many cases, however, doctors cannot pinpoint the reason for an epileptic attack. Some individuals might have a seizure once and never have another. Other people may have repeated episodes.

There are several types of epilepsy, including grand mal, petit mal, and infantile spasms. A grand mal attack is usually marked by rigid muscle contractions, loss of consciousness, and collapse. The attack may last from two to five minutes and is often followed by confusion and deep sleep. A petit mal attack usually comes as a lapse of awareness for less than a minute. The victim then resumes whatever activity he was engaged in before the attack without realizing anything out of the ordinary took place. Infants under the age of three sometimes have infantile spasms during which sharp muscle contractions force the body to jackknife for a few seconds.

Anticonvulsive drugs are used to treat and prevent epilepsy. Surgical removal of seizure-producing brain tissue may be indicated in extreme cases where drug therapy is ineffective.

Endocrine, Metabolic, and Deficiency Diseases

Disease can sometimes result from alterations in normal body metabolism caused by deficiencies in diet, hormones, and vitamins. It can also stem from malfunctions in the body’s immune system.

Endocrine Disorders

The endocrine system consists of a large number of glands that produce hormones—chemical compounds composed either of proteins or of steroids (a group of compounds derived from cholesterol) that travel through the blood to specific target organs (seehormones). Like the nervous system, the endocrine system allows organs to communicate; but while the nervous system is a rapid responder, endocrine “messengers” work at a slower pace.

For the system to function properly, hormone production must be exquisitely balanced. Both over- and underproduction of hormones can lead to disease.

Growth hormone disorders

Abnormal output of growth hormone from the pituitary gland early in life can result in one of two disorders— dwarfism if there is too little or gigantism if there is too much. Overproduction of growth hormone in middle- aged adults can cause acromegaly, a serious disorder in which bones, cartilage, and other organs become severely oversized.

Adrenal disorders

Excess production of cortisol, which is produced in the adrenal glands, results in Cushing’s syndrome; its symptoms range from severely weakened bones to increased blood sugar and high blood pressure. Inadequate production of cortisol leads to Addison’s disease, resulting in muscle wasting, fatigue, dangerously low blood pressure, and other signs.

Thyroid hormone diseases

Excess production of thyroid hormone, or hyperthyroidism, causes the body’s metabolic rate to skyrocket, often producing secondary cardiac disease, heat intolerance, and severe fatigue. Hypothyroidism (underproduction) causes cold intolerance, severe muscle cramping, weight gain, and memory loss, among other symptoms.

Sex hormone disorders

Both males and females produce both androgens and estrogens. Androgen is known as the male sex hormone because it is responsible for the development of male sexual characteristics, such as facial and body hair. Estrogen is called the female sex hormone because it aids breast development and other female sex traits. Over- and underproduction of either hormone in either gender can produce problems. For example, underproduction of androgens in males can result in a higher pitched voice; increased estrogen production may cause breast development in males. Increased androgens in females can result in hirsutism, or excessive body and facial hair. Abnormal sex hormone production in either gender can also affect libido, or sex drive.

Diabetes mellitus

A young person tests his blood glucose level.

One of the better known endocrine diseases is diabetes mellitus, a common disease caused either by a lack of insulin, or an inability to utilize insulin that is produced. Insulin is secreted by the pancreas and helps to move sugar from the blood into the cells, where it can be used for energy. There are three forms of diabetes—Type I, in which the pancreas cannot produce insulin; Type II, in which the pancreas produces insulin but the body’s cells are unable to utilize it; and gestational diabetes, which arises during pregnancy in some women. Dietary control is essential in all forms of diabetes; persons with Type I disease also may require daily injections of insulin. Long-term diabetes is often associated with blood vessel degeneration, which can lead to heart disease, stroke, blindness, kidney failure, gangrene of the feet, and serious neuritis. (See alsodiabetes mellitus.)

Metabolic Diseases Gout

This 18th-century engraving shows a man disabled by the painful metabolic disease known as gout.…

Courtesy of the Historical Division, The Cleveland Health Sciences Library

One of the oldest known human diseases is gout, which has been recognized by physicians for at least 2,000 years. For much of that time it was characterized as a “rich man’s disease,” because it was seen most commonly in wealthy people who tended to overindulge in a diet rich in meat and alcoholic drinks. Today scientists know that gout is caused by faulty metabolism of purine, a substance found in certain foods. Ineffective breakdown of purine results in the accumulation of uric acid in the blood and urate salts in the tissues. These salts frequently settle in the joints where they cause painful arthritis.

Gout may stem from an inborn error of metabolism or from other diseases. It usually strikes middle-aged men. The joint at the base of the big toe is the typical site of an acute attack of gout. The affected joint becomes red, hot, swollen, and painful. Fever accompanies the attack. Joints of other limbs might become similarly affected. Attacks of gout recur, but the sufferer enjoys complete relief in between them. Some patients develop chronic arthritis from gout. Gout is treated with drugs that reduce inflammation, and also with drugs that lower the uric acid level of the blood. In addition, sufferers must restrict their intake of certain foods and alcohol.

Cystic fibrosis

Cystic fibrosis is a genetic disorder involving the pancreas and the lungs. It appears during the first 10 years of life, though sometimes it is not discovered until later. The exocrine pancreatic glands, which produce important digestive enzymes, become plugged by thick mucus. This results in severe intestinal problems. Furthermore, because of similar mucus secretions, the lungs suffer scarring, infection, and eventually emphysema. Cystic fibrosis is treated with substitute pancreatic enzymes, as well as enzymes to clear lung secretions and antibiotics to control secondary infections.

Phenylketonuria and galactosemia

Phenylketonuria (PKU) and galactosemia also are genetically inherited metabolic diseases. Both result from the lack of a key enzyme needed to convert one type of chemical compound into another. PKU is caused by an inability to metabolize the amino acid phenylalanine. People with galactosemia cannot change galactose, one type of sugar, into glucose, another type. Both diseases can result in intellectual disability in children if not corrected in time. (See alsoheredity.)

Malnutrition and Deficiency Diseases

A diet deficient in vitamin D, calcium, or phosphorus, can result in rickets. The disease, which…

Robin Laurance—Impact Photos/Imagestate

Malnutrition can be defined as either overnutrition or undernutrition. Overnutrition—that is, the intake of more calories than are needed—results in overweight and obesity, which in turn can lead to high blood pressure, heart disease, and diabetes.

Undereating can stifle the development of both body and mind. Kwashiorkor is a condition that affects children mostly age five and younger whose diet is deficient in protein even though it may contain adequate calories. Children with kwashiorkor lack an appetite and appear lethargic and sullen; symptoms may include a swollen face, distended belly, muscle wasting, enlarged liver, and chronic diarrhea. Marasmus is a condition seen in young children whose diet lacks both adequate calories and protein. Children with marasmus are always hungry and generally more alert than victims of kwashiorkor; symptoms include extreme muscle wasting and a pinched expression that gives the face a wizened, “old” look.

Kwashiorkor and marasmus are common in underdeveloped nations, particularly after a famine or epidemic (see food and nutrition). Although less common, malnutrition can occur in the developed world; sufferers include people with chronic diseases such as AIDS, and those who are impoverished.

Vitamin deficiencies are uncommon among people in developed nations, except in the cases of pregnant women and those who breast-feed their babies. Since ample vitamins are in the general diet in those lands, there is no medical justification for daily doses of multivitamins to stimulate vigor or prevent colds or infections. In underdeveloped countries, however, such diseases as rickets (due to a lack of vitamin D) and scurvy (from deficient vitamin C) remain endemic. (See alsovitamin.)

Mineral deficiencies can also produce body disorders. Iron is indispensable for the prevention of anemia. Deficiency of magnesium, a cofactor in many enzymes, causes dizziness, weakness, and convulsions. Iodine is a major part of the thyroid hormones. Without it a person can develop a goiter. Fluorine is not considered essential, but it plays a great part in minimizing dental caries, or cavities. Trace elements, such as chromium, cobalt, and manganese, are also needed for a healthy body. Autoimmune Diseases

The immune system has numerous ways to differentiate between cells recognized as “self” and those recognized as foreign. In some individuals, for reasons that remain poorly understood, this system suddenly malfunctions—the body fails to recognize its own tissues, and makes antibodies targeting them. These malfunctions can affect any organ or tissue in the body, resulting in the suite of chronic disorders defined as autoimmune disease. Rheumatoid arthritis and systemic lupus erythematosus are two of the more than 80 such disorders that have been identified. Many scientists have concluded that multiple sclerosis and Type I diabetes are autoimmune in origin.

Rheumatoid arthritis is a chronic crippling disease that deforms bone joints and their adjacent tissues. It can strike nearly anyone at any age. It is marked by inflammation of an entire joint, including its synovial lining. Tendon coverings and bursas, or fluid-filled cushions, can become inflamed, too. Cartilage in the joint and adjacent bone is destroyed, causing painful stiffness and eventual ankylosis, or “freezing,” of the joint. Skin over the joint is taut, shiny, and clammy. The rheumatoid factor, a large protein molecule, is present in the blood of many adult patients; its detection aids in the diagnosis of the disease. Rheumatoid arthritis is usually treated with rest, physical therapy, and aspirin and other anti-inflammatory drugs.

Systemic lupus erythematosus (SLE), or lupus, is a serious degenerative disease that can strike one or many body systems over a period of years. The blood serum of afflicted persons contains a number of peculiar proteins, including the so-called L.E. factor, an antibody characteristic of the disease. Symptoms of SLE resemble other diseases, including cancer and tuberculosis, but can be distinguished by lesions around the nail beds and fingertips that are a hallmark of lupus. Other signs may include enlarged lymph glands in the neck and armpits and an enlarged spleen. SLE can damage the pericardium, heart valves, kidneys, and portions of the central nervous system. Although anyone may be affected, females between the ages of 20 and 40 years most often develop this incurable, yet controllable, disease. Bone and Muscle Diseases

Because of their close anatomic and functional relationships, bone and muscle share a similar vulnerability to disease and other malfunctions. Both are strongly affected by genetics and nutrition, and both can be seriously injured by a fall. Both bone and muscle are prone to a range of disorders, from congenital defects to infectious disease to cancer.

Because they are rigid, bones can break, or fracture. The degree of repair needed depends on what bone is broken—that is, its location and function in the body—and the extent of damage. Trauma—especially compound fractures, in which part of the broken bone pierces the skin—brings the risk of a bone infection, or osteomyelitis. Because bone has such a large blood supply, a bone infection can readily spread into the bloodstream and become systemic. For this reason, osteomyelitis is always treated with intravenous antibiotics.

Osteoporosis is a disease marked by an insuffiency of calcium in the bones.

Contunico © ZDF Enterprises GmbH, Mainz

Osteoarthritis is a painfully disabling disease of the spine and other weight-bearing joints. Cartilage in the joint is destroyed, followed by overgrowth of nearby bone. Another bone disease seen in aging persons is osteoporosis. In this disease, the bone becomes thin and brittle, making it easier for the individual to fall and sustain a fracture. Osteoporosis is especially common among older women due to hormonal changes that occur around menopause. Both diseases develop with advancing age but are highly preventable with the correct diet. Osteoporosis prevention is linked to getting adequate calcium in the diet, and to exercise.

Ankylosing spondylitis is a disabling and deforming disease of the spine, the pelvic joints, and sometimes the shoulders, hips, and knees. The lining of the affected joint becomes inflamed, the bone is weakened by loss of calcium, and the spine is bent forward. Eventually, the spinal vertebrae fuse and the spine becomes locked in the deformed position.

Temporary muscle disorders, such as tendonitis or torn muscles, result from injury or overexertion. True diseases of the muscles arise from a wide array of causes, from drug reactions to cancer. The cause of some diseases, such as fibromyalgia, a painful disease of the muscle fibers, is unknown.

A large number of muscle diseases result from a genetically inherited error in metabolism. One of the better known diseases in this group is muscular dystrophy (MD), a term that encompasses a group of diseases whose primary sign is severe muscle wasting and profound weakness. The disease has an early onset; in Duchenne muscular dystrophy, the most common form, signs are noted during early childhood. Most children who inherit this form lose the ability to walk by age 12 and must use a wheelchair for the rest of their lives. Different muscle groups progressively weaken; eventually the respiratory muscles fall to the disease, and the patient dies, usually before reaching the late 20s. Signs of Becker muscular dystrophy, a milder form of Duchenne, may not be apparent until the child has begun school, or even into the 20s. Symptoms are frequently less severe than those of the Duchenne form, and sufferers may live a normal life span. Muscular dystrophy is treated symptomatically; physical therapy and steroids may offer some relief. Despite intensive research, a cure remains elusive. Kidney and Genital Diseases

Disease can affect any of the parts of the closely related urinary and genital systems. Both can be infected or may malfunction because of a shortcoming in development.

Kidney Disorders Inflammatory diseases

Glomerulonephritis is a serious inflammatory disease of the kidneys. It generally is triggered by a prior infection— usually bacterial—which inflames the glomeruli, the tiny tufts through which blood is filtered (seekidney). The

inflammation may go away after a few weeks or may slowly destroy all the glomeruli. In the early stages, the inflammation may reduce filtration enough to cause blood to retain some excess fluid, salts, and wastes. Blood pressure might also rise. If the inflammation persists, the glomeruli are destroyed, blood pressure soars, and urine formation may stop. Mechanical means must be taken to cleanse the blood.

Pyelonephritis is a bacterial infection of the inner portions of the kidneys and the urine. If quickly treated, the infection can be cured. If untreated, however, the infection may scar and eventually destroy kidney tubules, resulting in a need for mechanical cleansing of the blood. Once damaged by pyelonephritis, the kidneys are easily reinfected.

Calculi

Calculus disease occurs when certain substances in urine crystallize into compact stones called calculi. A stone may be formed within a kidney and become swept by urine into the ureters and the bladder. It may cause pain, obstruct urine flow, or grow large enough to damage the kidney or bladder. Small calculi may be passed in urine, and large ones can be pulverized without surgery by means of energetic sound waves. Calculi can consist of calcium, urates, cystine, or other crystals. The tendency to form kidney stones sometimes runs in families

Other kidney disorders

Preeclampsia, or toxemia of pregnancy, is a disorder experienced by some women in the last half of pregnancy. During a pregnancy, the kidneys must work more than usual. However, the kidneys of a woman entering pregnancy with a preexisting kidney disease may be unable to increase their function. This leads to increased blood pressure and protein in the urine—conditions that affect the mother and the fetus. In severe cases, the fetus may die, or may need to be aborted to save the mother’s life. In lesser cases, however, medical treatment poses little risk to either life. Once a woman develops preeclampsia, she is likely to develop it again in later pregnancies.

Polycystic disease, an inherited failure of normal kidney development, strikes infants as well as adults. Many fluid-filled cysts spring up throughout the kidneys and cause them to malfunction. Polycystic disease sufferers eventually become uremic.

Uremia literally means “urine in blood.” It describes the condition in which the kidneys fail to operate effectively. This leads to a buildup in the blood of nitrogenous waste products from protein metabolism, which are usually removed by the kidneys. The concentration of many electrolytes, or salts, also increases in the blood. Symptoms include nausea, confusion, and breath or perspiration that smells of urine. Many types of kidney ailments can cause uremia. Special machines can be used to cleanse the blood of uremic patients (seebioengineering). In severe cases, patients may require a kidney transplant.

Reproductive System Disorders

Sometimes portions of the reproductive system fail to develop normally. In some rare cases, the gonads—the male’s testes and the female’s ovaries—or other sexual characteristics fail to develop at all. Without gonads, a person neither achieves puberty nor develops secondary sexual characteristics, such as breasts and uterus growth in females and penis growth and muscle development in males.

Infections such as gonorrhea can cause sterility by blocking the oviducts in females or the vas deferens in males. In males, gonorrhea may also interfere with urination. (See alsosexually transmitted disease.)

The prostate gland at the neck of the bladder in males enlarges slowly with age. It eventually may hamper urination and need surgical correction. (See alsoreproductive system.)

©Research 2020 Encyclopædia Britannica, Against Inc. Disease 29 of 61 Britannica LaunchPacks | The Treatment and Prevention of Disease

Research Against Disease

Although medical science has made great strides to eradicate disease, many ailments remain unconquered. Medical scientists have not yet discovered what causes sudden death syndrome, or crib death, a disease that fatally strikes infants less than a year old. They know what causes AIDS but have not yet found a cure for it. Nevertheless, research is under way against these and other baffling diseases in the hope that someday they will be wiped out or at least made manageable.

Medical scientists perform many kinds of experiments when they are researching a disease. They may grow cells in test tubes, infect them with germs or chemicals, and watch the aftereffects. Or they might infect a laboratory animal with a disease and observe how its body fights off or succumbs to the ailment. Medical scientists also may test the effects of a drug, a pathological environment, or a possible disease organism on human volunteers. However, human volunteers must be fully aware of the harmful as well as helpful consequences possible before taking part in the research. Prior experiments will have been made on laboratory animals to establish some idea of the project’s safety, and before the study can begin, the volunteers must give their informed consent to any unconventional treatment.

Medical research is an ongoing and global endeavor. Among the largest research institutions are the Institut Pasteur in France, the Max Planck Institute for Medical Research in Germany, and the Howard Hughes Medical Institute in the United States. Government agencies such as the U.S. National Institutes of Health also engage in disease research (seehealth agency). Medical schools and major hospitals maintain research programs for the benefit of their patients with unchecked or rare diseases. Research programs are also undertaken at many universities.

In the late 20th century, researchers made great strides in biotechnology, especially in genetic engineering. Although not without controversy, the use of genetically manipulated microorganisms in medicine has had considerable success. The most notable example is the production of genetically engineered insulin, which has been used successfully for more than 20 years in the treatment of diabetes.

Prior to the 1980s, the insulin used by diabetics was extracted from the pancreas of animals, usually pigs or sheep. Researchers then developed a technique for inserting the human gene for insulin into the plasmid of the bacterium Escherichia coli. The bacteria are cultivated of a special solution in large vats that hold millions of microbes, each of which then produces human insulin from the inserted gene. The bacteria excrete the insulin into the solution; it can then be purified and used by humans. Studies have shown that the human insulin has better success than pig insulin in treating the disease in humans. Furthermore, it is less costly to produce and eliminates the use of animals in its production. (See alsogenetic engineering; health; hospital; medicine; nursing; physiology; surgery.) Additional Reading

BERGER, MELVIN, AND HAFNER, MARYLIN. Germs Make Me Sick!, rev. 4th ed. (Harper Collins, 1996).BERKOW, ROBERT,

CHIR, B., AND FLETCHER, A.J., EDS.Merck Manual: General Medicine, 16th ed. (Merck, 1992).HOFF, BRENT, AND SMITH,

CARTER. Mapping Epidemics: A Historical Atlas of Disease (Watts, 2000).HYDE, M.O., AND FORSYTH, E.H.The Disease

Book: A Kid’s Guide (Walker, 1997). KARLEN, ARNO.Man and Microbes: Disease and Plagues in History and Modern

Times (Simon & Schuster, 1996).MCKEOWN, THOMAS. The Origins of Human Disease (Basil Blackwell, 1991).PORTER,

ROY.The Greatest Benefit to Mankind: A Medical History of Humanity (Norton, 1999).WARD, BRIAN.Epidemic (DK

Publishing, 2000).ZINSSER, HANS. Rats, Lice, and History (Penguin, 2000).

Citation (MLA style):

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medicine

The practice of medicine—the science and art of preventing, alleviating, and curing disease—is one of the oldest professional callings. Since ancient times, healers with varying degrees of knowledge and skills have sought to restore the health or relieve the distress of the sick and injured. Often, that meant doing little more than offering sympathy to the patient while nature took its course. Today, however, practitioners of medicine have several millennia of medical advances on which to base their care of patients.

In a physician's office, a routine checkup includes an examination of the mouth, throat, and…

A doctor in India gives drops of polio vaccine to a child.

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In most developed countries, physicians are the key health care providers. Through intensive schooling and training, they become highly skilled. Those who want to practice medicine must meet educational, professional, and ethical standards before their state, province, or country awards them a license to treat patients. Approaches to medical education, licensing, and practice vary throughout the world. This article focuses on physicians’ training and practice within the United States.

Medical School

A physical therapist assists a senior citizen with rehabilitation exercises at a physical therapy…

In 2008 there were 129 accredited medical schools granting doctor of medicine (M.D.) degrees and 25 colleges granting doctor of osteopathic medicine (D.O.) degrees in the United States. M.D.s, also known as allopathic physicians, treat disease mainly with drugs, surgery, and other well-established remedies. D.O.s, like their M.D. colleagues, are fully licensed medical physicians and surgeons who practice in most clinical specialties. Osteopathic medicine emphasizes the interrelationships of bodily structures and functions, and its practitioners receive special training in manipulative treatments of the musculoskeletal system.

All medical schools require students to take the Medical College Admissions Test (MCAT), a four-and-one-half- hour, computer-based exam that assesses problem-solving ability, critical thinking, writing skills, and knowledge of scientific concepts. In addition to scoring well on the MCAT, medical school applicants generally must have completed undergraduate courses in biology, physics, chemistry (including organic chemistry), and English and earned a bachelor’s degree.

In 2007 about 42,000 students applied to allopathic medical schools; just under 18,000 were accepted. Approximately 12,000 students applied for some 4,400 spots in osteopathic schools. Medical-school opportunities for women improved significantly in the late 20th century. In 2006, 48.8 percent of allopathic medical school graduates were women (up from 5.5 percent in 1962), and women constituted 47.5 percent of about 2,800 osteopathic graduates in 2006 (up from less than 2 percent of 427 total graduates in 1968).

Although programs aimed at increasing the diversity of the medical school student body have made some inroads, enrollment of minorities other than Asians remains far from optimal. In 2006, approximately 7.2 percent of students entering allopathic schools were black, 7.5 percent Hispanic, and 20 percent Asian; the percentages of osteopathic students were 4 percent, 4 percent, and 18 percent, respectively. Because racial and ethnic minorities would constitute half of the U.S. population by 2050, and research had shown that greater diversity within the physician workforce contributes to greater access to health care for the underserved, the Association of American Medical Colleges (AAMC) and the American Medical Association (AMA) were committed to increasing the number of minority physicians and raising the general cultural competence of all physicians.

During the first two years of a typical four-year curriculum, medical students concentrate on the sciences basic to medicine—anatomy, biochemistry, physiology, microbiology, pathology, pharmacology, and the behavioral sciences. They learn about normal structure and function of the human body and how those are altered by disease. They gain firsthand knowledge of the intricate human anatomy by dissecting dead bodies (cadavers). First- and second-year students also spend some of their time in a hospital observing experienced doctors and learning the fundamentals of taking a medical history and examining patients. In the third year, they gain extensive experience with patients in hospital, clinic, and office settings in internal medicine, family medicine, pediatrics, obstetrics and gynecology, surgery, and psychiatry. Fourth-year students spend most of their time in a clinical setting; they also take elective courses. The osteopathic curriculum is virtually the same as the allopathic, except that osteopathic students also learn muscle and joint manipulation.

Medical education is expensive. In 2007 the average cost of tuition, fees, and health insurance for a first-year student at a private allopathic medical school was about $40,000 and for a state resident attending a tax- supported public medical school about $22,000. Annual tuition and fees for D.O. programs ranged from $20,000 to $35,000. According to AAMC statistics, approximately 85 percent of M.D.s were graduating with significant debt (between $120,000 and $160,000). Even though physicians’ eventual earnings are among the highest of any occupation, their debt was increasing at a much higher annual rate than their incomes. A 2007 AAMC report concluded that without drastic changes, significant numbers of young physicians could be faced with unmanageable debt.

Graduate Medical Education

Newly graduated doctors must complete a residency in the specialty they have chosen before they can be licensed to practice. Most find a residency through the computer-coordinated National Resident Matching Program (NRMP). In 2008 about 50,000 applicants sought about 25,000 residency positions through the match.

The residency served by a new doctor is a fast-paced medical apprenticeship. For M.D.s, this paid, on-the-job training lasts from three to seven years, depending on the specialty. Residencies in the surgical specialties are the longest—five or more years. Those in internal medicine, family medicine, pediatrics, and psychiatry are generally three years. Doctors who choose to specialize further enter post-residency fellowships (the NRMP conducts matches for fellowship positions in 34 subspecialties).

Most graduates of osteopathic colleges serve a 12-month internship followed by a two- to six-year residency in one of nearly 700 American Osteopathic Association (AOA)–approved programs. Graduates of medical schools outside the United States and Canada (both U.S. citizens and non–U.S. citizens) may apply for residencies after they have met certain qualifications and been certified by the Educational Commission for Foreign Medical Graduates. Between 2004 and 2008 about 4,300 international medical graduates per year found residences through the NRMP.

Licensing of Physicians

Each of the 50 states, the District of Columbia, and the U.S. territories has its own requirements for obtaining a medical license, its own board that grants the license, and its own laws governing the practice of medicine. Because of the wide variations in the licensing process among states, few generalizations can be made about it. Since 1994, however, all states have required M.D.s to pass the United States Medical Licensing Examination (USMLE). The first two steps of the three-step test are typically taken during the second and fourth years of medical school and the third step during residency. Most state licensing boards for osteopaths require applicants to pass the Comprehensive Osteopathic Medical Licensing Examination, a three-part test comparable to the USMLE.

Certification of Specialists

Medical specialists are not certified by their state but by the profession itself. Each major allopathic specialty has its own certification board. The American Board of Medical Specialties (ABMS) oversees 24 of those boards and assists them in developing standards to certify doctors in 146 specialties and subspecialties. Certification by an ABMS member board involves rigorous testing and peer evaluation; about 85 percent of licensed M.D.s are certified by at least one ABMS board. D.O.s. gain certification from one of 18 specialty boards overseen by the AOA. What Doctors Do

Diagnosis

Physicians do several things in the course of serving a patient. The first is to make a diagnosis—that is, identify the exact nature of the problem. They obtain a medical history by asking pertinent questions about a patient’s current and past health and illnesses, personal habits, lifestyle, family, and job or school. The history will indicate how and when the patient became sick and whether or not he or she ever previously had the same or a similar condition.

The history will reveal symptoms (abnormal body changes that patients detect) such as pain, fatigue, loss of appetite, and nausea. These are clues that help doctors decide what signs (abnormal body changes that physicians detect) they should look for. By simple inspection doctors may observe a rash or swelling of the ankles. They may discover a cyst or tumor by palpation (feeling the body tissue); detect a heart murmur by listening to the chest with a stethoscope (auscultation); or determine the presence of infection in the body through blood chemistry studies. A case of appendicitis would be diagnosed on the basis of a patient’s complaints of abdominal pain, appetite loss, nausea, and vomiting (symptoms), which would prompt the physician to check for fever, tenderness in the lower right portion of the abdomen, and a high number of white cells in the blood (signs), which together would lead to a diagnosis of probable appendicitis.

Treatment

A well-trained physician will select the best forms of therapy that will correct a particular illness in a given patient. The clear choice for the patient with appendicitis would be surgery to remove the appendix. A delay in surgery could result in rupture of the appendix and serious infection. Because of the risk of infection during and after the operation, the physician is also likely to prescribe antibiotic therapy. Increasingly doctors are practicing “evidence-based medicine”—an approach that involves conscientious use of results from well-controlled clinical trials in making treatment decisions. Proponents of evidence-based medicine consider it the most objective way to ensure that patients receive optimal care. In recent years, many specialties have issued detailed “clinical practice guidelines” based on the best evidence available. These compilations enable clinicians to readily choose treatments backed by solid science.

Before a physician proceeds with a treatment, he or she must (by law) convey the details of the planned procedure (including all the risks) to the patient in language the patient comprehends. The patient then must sign an “informed consent” document acknowledging that he or she is going ahead with the treatment with full awareness of the potential outcomes.

Prognosis

The prognosis is the doctor’s prediction of the probable outcome of a case based on his or her knowledge of the disease, previous experiences treating it, and the health status of the patient. When appendicitis strikes an

otherwise healthy child, the doctor can usually make an optimistic prognosis. If, however, an obese adult with high blood pressure develops appendicitis that is not diagnosed promptly, the potential for rupture of the appendix and infection is high. Moreover, the patient’s excess weight and elevated blood pressure increase the risk of surgical complications. In this case the prognosis would be uncertain, as the doctor would not be able to predict how the patient would endure surgery, how extensive infection might be, or how long the healing process would take.

Types of Practice

Some doctors choose to go into private practice in which they set up individual offices and cater to the medical needs of as many people as they can. Private practitioners are paid on a fee-for-service basis (patients’ health insurance reimburses them for each service provided). Such solo practices give physicians a great deal of independence and allow close rapport with patients. At the same time, they tend to work extremely long hours and are virtually always “on call.”

More commonly, recently licensed doctors enter a group practice in which they share support staff, patients, and certain medical responsibilities with other doctors. Group practices tend to be able to afford expensive equipment that private practitioners generally would not have. Doctors in a group may be paid on a traditional fee-for-service basis, or they may be salaried.

New doctors may take a salaried position within a health maintenance organization (HMO). HMOs provide medical treatment on a prepaid basis; enrolled patients pay a fixed monthly fee regardless of whether they need medical care that month. HMO members must choose a primary care physician, who acts as the “gatekeeper” for the organization by determining what tests and treatments patients do and do not need and when they should see a specialist. For doctors, the advantages of such a practice include regular hours of work, steady income, availability of sophisticated diagnostic equipment, and easy access to group consultation.

Levels of Care and Coverage

In the United States and many other countries physicians provide three levels of care. The primary level is the broadest and meets the complete medical needs of the vast majority of people. Primary care is most often provided by general practitioners such as family practice doctors, internists, or pediatricians, who are patients’ first contact with the medical system. Secondary care is provided by a physician who acts as a consultant at the request of the primary physician; the provider of this level of care might be a radiologist, a cardiologist, urologist, or dermatologist. The third level, tertiary care, is usually based at a teaching hospital or center that has personnel, facilities, and technology for special investigations and treatments; comprehensive cancer care is an example.

The levels of care patients receive depend on their insurance coverage. Until recently, the United States was the only industrialized country in the world without some form of universal health care (coverage that extends to all citizens). In 2007, 84.7 percent of the population was covered by private or public health insurance; the rest either had no health insurance or were underinsured. The latter group included middle- and higher-income people, half of whom went without needed care due to the cost. To address these circumstances, U.S. President Barack Obama made health care reform a top priority of his administration. The historic Patient Protection and Affordable Care Act, signed into law in 2010, was designed to extend health care to most uninsured Americans.

Too Few Physicians?

From the late 1970s to the mid-1990s, several expert panels forecast a glut of physicians in the United States in the new millennium. Consequently, medical schools capped enrollment, and Congress limited its funding of

medical residencies. The experts, however, miscalculated. Between 2000 and 2007, 15 states and 16 medical specialty boards issued reports detailing how looming or already-evident physician shortfalls would affect them. Three national reports projected that by 2020 there would be as many as 200,000 too few physicians to meet the needs of the aging population. To remedy the shortfall, medical schools began increasing enrollment. In 2007 allopathic medical schools admitted 17,800 students, the largest class ever, while first-year enrollment in osteopathic medical schools reached nearly 4,500 students (up from just under 3,000 students in 2000).

In addition to the existing and anticipated physician shortages, there was also a serious misdistribution of them. The ratios of physicians to population were highest in the New England and the Middle Atlantic states (Massachusetts had 443 doctors per 100,000 population) and lowest in the South Central and Mountain states (Mississippi had 182 doctors per 100,000). In 2005 nearly 60 million Americans lived in government-designated health professional shortage areas (HPSAs). The National Health Service Corps (NHSC), now a part of the Health Services and Resources Administration, was created in 1970 to address the physician distribution problem. NHSC offers primary care physicians incentives such as help with repayment of loans to serve in HPSAs. From its inception through 2007, 27,000 NHSC-recruited doctors had served up to five million people who were uninsured or underinsured or faced language, geographic, or cultural barriers to care.

Changing Face of Medicine

Americans were not receiving their medical care from allopathic and osteopathic physicians only; since the early 1990s, surveys had shown that 30 percent to 60 percent of adult Americans were using complementary and alternative medicine (CAM). Complementary treatments are used in conjunction with conventional medicine; alternative treatments are used in place of it. Many of the unconventional therapies had gained such wide acceptance that, according to an editorial in the Journal of the American Medical Association in 2008, they had become “part of the conventional medicine armamentarium.”

A man measures ingredients in a traditional Chinese pharmacy. Traditional Chinese medicine uses an…

The number of practitioners of CAM is unknown, and the quality and quantity of their training varies widely. They include chiropractors, naprapaths, massage therapists, Chinese herbalists, energy healers, homeopaths, acupuncturists, yoga therapists, and others; they treat back problems, allergies, arthritis, insomnia, headaches, high blood pressure, depression, and even cancer. In 1992 the U.S. National Institutes of Health, the country’s premier medical research establishment, created the Office of Alternative Medicine to study therapies outside the realm of conventional medicine. The office was expanded to the National Center for Complementary and Alternative Medicine (NCCAM) in 1998. In its first decade NCCAM sponsored more than 1,200 clinical trials assessing the validity of widely used but unproven therapies.

The Internet and other communications technologies have profoundly altered the practice of medicine. They allow rapid dissemination of information, which has the potential to increase physicians’ efficiency in caring for patients as well as enhance the quality of care provided. In the burgeoning field of telemedicine, physicians provide consultative services and exchange medical information via electronic communications. Doctors can send live video and high-resolution images to distant locations and examine patients who are hundreds or thousands of miles away. Telemedicine has the potential to alleviate regional inequalities in medicine and bring the advantages of urban medical centers to those with little or no access to care.

The Internet has also empowered patients, who have virtually unlimited access to medical information. While many sites provide valuable information, others may disseminate unreliable or misleading information. The National Institutes of Health recommends that consumers ask questions about the sites they visit: Who runs the site? Who pays for it? What is the basis of the information? How current is it? The National Library of Medicine offers MEDLINEplus, a resource that links the general public to sites that have been carefully reviewed. History of Medicine in Brief

A surgeon performs a trepanning, or trephining, procedure on a patient by drilling into his skull.…

Wellcome Collection, London (CC BY 4.0)

Evidence of attempts to care for the sick and injured predates written records. Skulls found in Europe and South

America dating as far back as 10,000 BC have shown that the practice of trepanning, or trephining (removal of a portion of the skull bone), was not uncommon. This operation, performed by many early peoples, including American Indians, was probably done to release evil spirits that were thought to be the source of illness; yet, in many cases, it proved to be the medically correct thing to do. Opening the skull can relieve pressure and pain caused by brain tumors and head injuries.

Indeed, much of early medicine was closely identified with pagan religions and superstitions. Illness was attributed to angry gods or evil spirits; prayers, incantations, and other rituals were used to appease the gods or ward off demons—and thereby drive off disease. Nonetheless, the ancients did not entirely lack valid medical knowledge. In fact, through observation and experience, they acquired considerable wisdom about sickness and its prevention and relief. (See alsofolk medicine.)

The book of Leviticus in the Old Testament described quarantine regulations and sanitary practices that were used to prevent the spread of leprosy and plague. The ancient Romans realized the importance of sanitation to health and built sewers, systems that drained waste water from public baths, and aqueducts that provided clean water.

Egyptian Medicine

The ancient Egyptians were among the first to use certain herbs and drugs, including castor oil, senna, and opium. They also set and splinted fractured bones using techniques remarkably similar to those of modern

medicine. Egyptians were reputed to be skilled diagnosticians; a medical papyrus from about 1600 BC, which is

believed to be a copy of a text from about 3000 BC, described 58 sick patients, of whom 42 were given specific diagnoses. Although the Egyptians practiced mummification, which involved removing and dehydrating most of the internal organs of the dead, they apparently did not study those organs, as their anatomical knowledge was quite limited.

Greek and Roman Medicine

Hippocrates (460–375 BC), known as the “father of Western medicine,” was an admired physician and teacher who rejected the notion that disease was punishment sent by the gods; rather, he believed it had natural causes. Hippocrates put forth a doctrine that attributed health and disease to four bodily humors, or fluids— blood, black bile, yellow bile, and phlegm. He believed that the humors were well balanced in a healthy person, but various disturbances or imbalances in them caused disease. At that time, his humoral theory seemed highly scientific. In fact, doctors diagnosed and treated illnesses based on the four humors well into the 19th century.

Knowing that he could not cure most diseases, Hippocrates tended to recommend conservative measures such as exercise, rest, and cleanliness. By contrast, for fever, which he thought was caused by an excess of blood in the body, he recommended the drastic measure of bloodletting. The practice of bloodletting (or bleeding), which was thought to have many therapeutic effects, was used for more than two thousand years and undoubtedly hastened the deaths of countless patients who might otherwise have recovered.

Hippocrates is best known today for his ethical code (Hippocratic Oath), which continues to be used by the medical profession as a guide to appropriate conduct. The oath is a pledge doctors make to always use their knowledge and best judgment for the benefit of their patients and to never harm or injure those in their care.

For a brief period after Hippocrates’ death, two Greek physician-scholars living in Alexandria, Herophilus and Erasistratus, performed the first known systematic dissections of human bodies. They dissected virtually every organ, including the brain, and recorded what they learned. Despite their dedication to the science of anatomy,

these pioneers had little influence on the subsequent practice of medicine. By 150 BC, dissection of human cadavers was banned throughout the Hellenistic world, and any writings they left behind were lost when

Alexandria’s library was destroyed in the 3rd century AD.

One of those trained in Hippocratic medicine was Galen (129–216? AD), a Greek who traveled widely and became the most renowned physician in Rome. Although Galen accepted and embellished the four-humors doctrine, he also made important discoveries. He performed systematic experiments on animals (including apes, monkeys, dogs, pigs, snakes, and lions), which involved both dissection and vivisection (live dissection). He treated gladiators and took advantage of the opportunity to study the internal organs and muscles of the wounded. Galen recognized connections between bodily structures and functions; for example, he demonstrated that a severed spinal cord led to paralysis. He recognized that the heart circulated blood through the arteries but did not understand that it circulated in only one direction. Galen produced a prodigious body of medical scholarship that was adhered to by medical practitioners for 1,600 years. Unfortunately, his erroneous beliefs as well as his accurate insights were perpetuated.

Arabian Medicine

After the breakup of the Roman Empire, the tradition of Greek medicine continued in the universities of the Arab world. The Persian physician Rhazes, or Al-Razi (865?–923?), is credited with being the first to distinguish between the highly contagious viral diseases smallpox and measles. He also recognized the need for sanitation in hospitals. Probably the most important physician at the beginning of the second millennium was Avicenna. His monumental Canon of Medicine, a five-volume encyclopedia of case histories and therapeutic instructions, was long considered an absolute medical authority in both Eastern and Western traditions.

Medicine in Medieval and Renaissance Europe

At about the same time that Arabian medicine flourished, the first medical school in Europe was established at Salerno, in southern Italy. Although the school produced no brilliant genius and no startling discovery, it was the outstanding medical institution of its time. In about 1200 Salerno yielded its place as the premier medical school of Europe to Montpellier, in France. Other great medieval medical schools were founded at Paris, France, and at Bologna and Padua, in Italy.

Midwives assist in a childbirth while astrologers in the background consult sky charts, in a woodcut …

National Library of Medicine, Bethesda, Maryland

Even with the presence of these institutions, medicine progressed very slowly in Europe during the Middle Ages. Medieval physicians continued to rely upon ancient medical theories, including that of the humors. They analyzed symptoms, examined waste matter, and made their diagnoses. Then they might prescribe diet, rest, sleep, exercise, or baths, or they could administer emetics (something to cause vomiting) and laxatives or bleed the patient. Surgeons could treat fractures and dislocations, repair hernias, and perform amputations and a few other operations. Some of them prescribed opium or alcohol to deaden pain. Childbirth was left to midwives, who relied on folklore and tradition.

The Christian church also influenced European medicine during the Middle Ages. It is sometimes said that the early church had a negative effect on medical progress. Disease was regarded as a punishment for sin, and healing required only prayer and repentance. A number of saints became associated with miraculous cures of

certain diseases, such as St. Vitus for chorea (or St. Vitus’s dance) and St. Anthony for erysipelas (or St. Anthony’ s fire). In addition, the human body was held sacred and dissection was forbidden. Nevertheless, the medieval church played an important role in caring for the sick. Great hospitals were established during the Middle Ages by religious foundations, and infirmaries were attached to abbeys, monasteries, priories, and convents. Doctors and nurses in these institutions were members of religious orders and combined spiritual with physical healing.

It was not until the Renaissance that Europeans began to seek a truly scientific basis for medical knowledge instead of relying on the teachings of Galen and other ancient physicians. The Flemish physician Andreas Vesalius discovered many new principles of anatomy through dissections, which he compiled in his profusely illustrated Seven Books on the Structure of the Human Body, published in 1543.

Ambroise Paré (1510–90), a Frenchman, practiced as an army surgeon and became an expert at treating battlefield wounds. He proved that tying blood vessels was a better method of stopping profuse bleeding than cauterizing them with hot oil or a hot iron—a discovery that spared countless soldiers terrible pain and suffering.

17th- and 18th-Century Medicine

Based on painstaking observations of his own veins and study of the blood vessels of sheep, English physician William Harvey determined that blood was pumped away from the heart via the arteries and was returned to it by way of the veins. Groundbreaking as this discovery was, Harvey could not explain how blood passed from the arteries to the veins. Four years after Harvey’s death in 1657, the Italian researcher Marcello Malpighi, with the aid of a microscope, identified and described the pulmonary and capillary network that connected small arteries with small veins. (See alsocirculatory system.)

The art of surgery developed in 17th-century England at a time when elsewhere in Europe operations were being performed mainly by barbers. William Cheselden, a surgeon and anatomist, was known for his swift and skillful operations; it was reported that he could perform a lithotomy (removal of a stone from the urinary bladder) in 54 seconds.

Edward Jenner, an English country physician, noticed that women who milked cows often caught cowpox (a relatively mild illness) but never got the much more virulent human disease smallpox. Based on that observation, he began developing the world’s first vaccine against a virulent infectious disease. In 1796 Jenner inoculated an eight-year-old boy who had never had smallpox with material taken from cowpox lesions on the hands of a dairymaid. Several weeks later, he exposed the boy to smallpox, and he remained healthy.

19th-Century Medicine

Before the mid-1800s surgery had to be performed without anesthesia. Patients may have been given a blow on the head, a dose of opium, or a swig of whiskey or rum—at best, minimally effective means of reducing pain. The best surgeons, therefore, were those who completed their work in the least amount of time. Early in the century British and American scientists began experimenting with two pain-numbing substances, the gas nitrous oxide and the liquid solvent ether. In 1846, before a large group of doctors at Massachusetts General Hospital in Boston, William Morton (who did not have a medical degree but had apprenticed with a dentist) demonstrated ether anesthesia in a patient undergoing surgery to remove a tumor from his neck. The resoundingly successful operation was painless for the patient. Word of this achievement spread quickly, and soon dentists and surgeons on both sides of the Atlantic were using anesthesia. In 1847 chloroform was introduced and became the anesthetic of choice.

Certainly one of the most important advances of the 19th century was the development and acceptance of the “germ theory of disease.” In the 1840s Ignaz Semmelweis, a young physician working in a hospital in Vienna,

recognized that doctors who performed autopsies and then delivered babies were responsible for spreading puerperal (childbed) fever, an often deadly infection of the reproductive organs. After Semmelweis ordered doctors to wash their hands with a chlorinated lime solution before entering the maternity ward, deaths from puerperal fever plummeted.

French chemist and microbiologist Louis Pasteur first learned about germs by studying the fermentation of beer, wine, and milk. He went on to explore infectious diseases in farm animals and develop vaccines against anthrax in sheep, erysipelas in swine, and chicken cholera in poultry. Finally Pasteur turned his attention to rabies in humans. His crowning achievement was the development of a vaccine against the always-fatal viral infection caused by bites of rabid animals. In 1885 Pasteur was urged by doctors to give his experimental vaccine, which had only been tested in dogs, to a young boy who had been bitten more than a dozen times by a rabid dog. He administered a series of 13 daily injections of increasingly virulent material obtained from the spinal cords of rabid rabbits. The child endured the prolonged and painful treatment and made a full recovery.

German physician Robert Koch discovered that dormant anthrax spores could remain in the blood of sheep for years and, under the right conditions, develop into the infectious organisms that caused deadly anthrax outbreaks. In 1876, when he presented his findings on the anthrax disease cycle to doctors in Breslau, Germany, an eminent pathologist commented: “I regard it as the greatest discovery ever made with bacteria and I believe that this is not the last time that this young Robert Koch will surprise and shame us by the brilliance of his investigations.” He was right. Koch went on to discover the bacteria responsible for tuberculosis (TB; 1882) and human cholera (1883) and to do groundbreaking research on leprosy, plague, and malaria.

The French microbiologist Charles Laveran discovered the disease-causing protozoanPlasmodium, the parasite carried by mosquitoes responsible for malaria. At the turn of the century, the American army doctor Walter Reed headed a team of physicians who proved that yellow fever was also transmitted by mosquitoes.

The first serious studies of mental disease were conducted during the 19th century. Jean Charcot used hypnosis as a tool to search the troubled minds of mental patients. His student Sigmund Freud developed the psychoanalytic technique for treating mental illness.

20th- and 21st-Century Medicine

In 1900 the average life expectancy of persons born in the United States was 47 years; by the end of the century it was 77 years. The U.S. Centers for Disease Control and Prevention (CDC) attributed 25 of those 30 additional years of life that Americans had gained to 10 momentous 20th-century public health achievements: control of infectious diseasesimmunizationsthe decline in deaths from heart disease and strokesafer and healthier foodshealthier mothers and babiesincreased safety of motor vehiclessafer workplacesfamily planningfluoridation of drinking waterthe recognition of tobacco use as a health hazard

Paul Ehrlich’s discovery in 1910 of Salvarsan, the first drug effective against syphilis, inaugurated the era of modern antimicrobial drug therapy. The sulfa drugs, which provided strong protection against streptococci and other bacteria, were introduced in the 1930s. In 1938 Ernst Chain and Howard Florey succeeded in synthesizing and purifying the Penicillium mold that Alexander Fleming had discovered 10 years earlier; their product, the broad-spectrum antibioticpenicillin, is still widely used today. In 1948 Selman Waksman discovered streptomycin, a powerful antibiotic that led to the control of TB.

In the early 1920s researchers Frederick Banting and Charles Best isolated the hormoneinsulin, which they used to save the lives of young people with diabetes mellitus. At the time, diabetes mainly affected children and adolescents; because their bodies did not produce insulin, which the body needs to convert food into energy, they died. Shortly after this triumph, the pharmaceutical manufacturer Eli Lilly and Company began large-scale

production of cow and pig insulin, which helped turn diabetes (the type now known as Type 1) from a fatal into a manageable disease that allowed young people to live into adulthood. By the end of the century, Type 2 diabetes (in which the body is unable to properly utilize the insulin it produces) had become a public health threat of epidemic proportions; 3.8 million people worldwide died from its complications each year.

The eradication of smallpox, one of the most deadly and debilitating scourges the world had ever known, represents one of the greatest accomplishments in modern medicine, science, and public health. Thanks to widespread vaccination, smallpox was eliminated from Europe, North America, Australia, and New Zealand by 1950 and from most of South and Central America by 1959. In 1967 the World Health Organization (WHO) launched a campaign to eradicate the disease that still infected up to 15 million people annually in 31 countries. Ten years later, the last case of smallpox was diagnosed in a young man in Somalia, and in 1980 WHO declared smallpox eradicated from the planet. Because humans were the only natural reservoir of the smallpox virus, once it was gone, people no longer needed to be vaccinated against it. The only remaining specimens of the virus were retained in high-security laboratories in the United States and Russia.

A global polio eradication initiative was begun in 1988, at which time about 350,000 children in 125 countries on five continents were crippled each year by the highly contagious viral disease that attacks the nervous system. By 1999 the number of cases had been reduced by 99 percent, and by the end of 2006, only four countries— India, Nigeria, Pakistan, and Afghanistan—still had endemic polio (uninterrupted transmission of the wild polio virus). Continuing efforts reduced the number of cases to just 222 in 2012, and the campaign’s sponsors (WHO, the United Nations Children’s Fund, CDC, and Rotary International) expressed confidence that a polio-free world could be achieved by 2018.

The early 1980s saw the emergence of the deadly new disease acquired immunodeficiency syndrome (AIDS), caused by the human immunodeficiency virus (HIV), which rapidly grew into a global pandemic. Thanks to the development of life-prolonging drugs, by the mid-1990s HIV/AIDS was no longer a death sentence in wealthy countries. In poor countries, however, the pandemic continued to wreak havoc. In 2001 more than 28 million people in sub-Saharan Africa were living with HIV/AIDS, but fewer than 40,000 had access to drug treatment. At the same time, much of Africa and many developing countries were profoundly affected by malaria and TB. The three pandemic diseases killed more than six million people every year.

In 2002 the Global Fund to Fight AIDS, Tuberculosis and Malaria was created to dramatically increase resources to combat the trio of devastating diseases. By mid-2008 the fund had distributed $6.2 billion to 136 countries. At least 1.75 million people were receiving drug treatment for HIV/AIDS, 3.9 million were receiving TB treatment, and 59 million insecticide-treated mosquito nets had been distributed to families in malaria-ridden countries. The program estimated it had saved more than 1.5 million lives.

Late in the 20th century, antimicrobial drugs employed to treat common infections were becoming increasingly ineffective, allowing the return of previously conquered diseases and the emergence of virulent new infections. By 2007 about five percent of the nine million new cases of TB in the world each year were resistant to at least two of the four standard drugs; treatment with other drugs was 200 times more expensive and had lower cure rates. In 2007 the CDC reported that the bacterium methicillin-resistantStaphylococcus aureus (MRSA) was responsible for more than 90,000 serious infections and 19,000 deaths in the United States annually. For years MRSA had been a problem in health care institutions such as hospitals, nursing homes, and dialysis centers, where it had grown increasingly resistant to commonly used antibiotics. Formerly it primarily infected people with weakened immune systems; by 2007, however, 13 percent of cases were occurring in healthy people living in the community.

In 1953 British graduate student Francis Crick and American research fellow James Watson identified the double- helix structure of DNA, a discovery that helped explain how genetic information is passed along. Exactly 50 years later, the Human Genome Project was completed. The 13-year international collaboration of more than 2,800 researchers, one of the boldest scientific undertakings in history, identified all humangenes (about 22,000) and determined the sequences of the 3 billion chemical base pairs that make up human DNA. The genetic information provided by the project has enabled researchers to pinpoint errors in genes that cause or contribute to disease. In the future, having the tools to know the precise genetic make-up of individuals will enable clinicians to deliver truly personalized medicine.

As an increasing number of genetic tests have become commercially available—some of which can be lifesaving—new ethical questions have been raised about the best ways to deliver them and how the genetic information they provide should be used by insurers, employers, courts, schools, adoption agencies, and the military. In response to those concerns, in 2008 the U.S. Congress passed and President George W. Bush signed into law the Genetic Information Nondiscrimination Act, which prohibits insurance companies and employers from discriminating on the basis of information derived from genetic tests.

Ellen BernsteinEd. Additional Reading

ADLER, ROBERT. Medical Firsts (John Wiley & Sons, 2004).GROOPMAN, JEROME. How Doctors Think (Houghton Mifflin,

2007).HARDING, ANNE S. Milestones in Health and Medicine (Oryx Press, 2000).JAUHAR, SANDEEP. Intern: A Doctor’s

Initiation (Farrar, Straus and Giroux, 2008).NULAND, SHERWIN B. The Uncertain Art: Thoughts on a Life in Medicine

(Random House, 2008).PORTER, ROY, ED. Cambridge Illustrated History of Medicine (Cambridge University Press,

1996).STRAUS, EUGENE W. AND STRAUS, ALEX. Medical Marvels: The 100 Greatest Advances in Medicine (Prometheus Books, 2006).

See also bibliographies for biochemistry; bioengineering; bioethics; brain and spinal cord; human disease; health; psychology.

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therapy

The treatment and care of someone to combat disease, injury, or mental disorder is known as therapy, or therapeutics. There are many kinds of therapies. Some of them, such as surgery or occupational therapy, are widely used, while such others as seawater treatments are less common.

Among the more widely used therapies are psychotherapy, the use of treatment by a therapist for psychological or emotional disorders; surgical therapy, the correction or removal of diseased tissues by surgical operation; diet therapy, the regulation of diet and fluid intake; biologic therapy, the use of such biologic products as serums, vaccines, and antitoxins; chemotherapy, the use of chemicals to attack specific diseases; physical therapy, the use of physical agents or exercise; and radiation therapy, the use of X rays and radioactive isotopes to destroy diseased tissues. Therapeutic methods also involve such agents and techniques as ultraviolet radiation, hypnosis, water baths, occupational and recreational activities, vitamins, aerosol mists, and nursing care.

Methods for preventing and curing disease have existed since ancient times. Throughout history people have found therapeutic value in various plants, animals, and minerals. With the development of modern medicine, as well as other discoveries and observations, many useful techniques have become available. During the 19th century various therapeutic techniques were developed. Major contributions were made by scientists like Louis Pasteur and Joseph Lister. As time progressed, drugs were purified, diseases were identified, and techniques for the diagnosis, treatment, and prevention of disease were found. Therapeutics also developed because of the work of people like Florence Nightingale. She and others brought attention to such issues as hygiene, health education, hospital facilities, surgical techniques, transportation of the sick and injured, and other related factors (seemedicine, “History”; nursing). Surgical Therapy

Surgery is a branch of medicine that treats injuries, deformities, and other disorders through manual and instrumental methods. In general, methods other than surgery are used to manage chronic, slowly progressing diseases. Patients with progressive diseases often require surgery.

Wound treatment seeks to heal and avoid infection during and after surgery. A wound created during an operation must be large enough to expose the area to be operated upon so that it can be seen and the tissues manipulated. Hence, there are many opportunities for infections to develop, as well as for injury to the areas surrounding the wound.

The removal of diseased tissue or organs is called extirpative surgery. This category includes cancer surgery and “radical” operations, those in which extensive surgery is performed. In a radical mastectomy, for example, the breast and the contents of the armpit, including the lymph nodes, are removed.

Reconstruction and replacement surgery is used to treat injuries or to correct the effects of degenerative diseases. Defective heart valves, for example, are sometimes replaced with valves made of plastic. In replacing tissue lost through such injuries as fractures or burns use is made of tissue grafts or plastics. Grafts may come from the patients themselves or from donors. Another example of this kind of surgery is hip joint reconstruction, in which a defective joint is replaced by one made of metal.

Physiologic surgery is a new surgical field. The objective of this surgery is to reduce suffering by eliminating some of the symptoms of disease or reducing their effects. An example of this kind of surgery is the cutting of the vagus nerve in a person who has a peptic ulcer. Severing this nerve reduces the production of gastric acid, a factor in the development of the ulcer, but does not attack the ulcer directly.

Transplantation surgery involves the moving of organs from one person to another, or the grafting of skin from one place on an individual’s body to another. Although progress has been made in transplanting organs, the problem of the body’s rejection of these organs has not been completely solved. (See alsosurgery; transplantation, tissue.) Chemotherapy © 2020 Encyclopædia Britannica, Inc. 44 of 61 Britannica LaunchPacks | The Treatment and Prevention of Disease

Chemotherapy

The treatment of disease through the use of chemical compounds is termed chemotherapy. Chemotherapeutic drugs destroy or inhibit the growth of colonies of specific microorganisms or parasites in or on the body of a patient. Some of these drugs, especially the anticancer drugs, are highly toxic because they interfere not only with the biochemical processes of diseased cells, but also with those of healthy cells. Chemotherapy is used against many types of bacteria, some viruses, some fungi, and many parasites. (See alsodrugs.) Substitution Therapy

In substitution therapy substances in which the body is deficient are replaced. Problems that arise from loss of blood or other fluids, minerals, proteins, vitamins, and hormones can be managed through substitution therapy. Radiation Therapy

Radiation therapy generally uses sources of ionizing radiation to treat disease. Ionizing radiation penetrates deep into tissues and brings about physical and chemical changes in cells—both healthy and diseased—that destroy them. Radiation therapy is often used to treat cancer and blood disorders, such as leukemia. Nonionizing radiation such as infrared radiation is used to relieve inflammation. (See alsoradiation; X rays.) Physical Therapy

A physiotherapist treats the shoulder of a senior patient.

A clinic in Germany uses exercise as physical therapy for back-pain patients.

Certain bodily ailments respond favorably to exercise and the application of such physical agents as heat and ultrasound. Such physical therapies are used to rehabilitate individuals who are disabled by pain or by other

ailments that affect the motor functions of the body. Physical therapy helps patients return to comfortable and productive lives, even though their medical problems may continue. Some common methods of physical therapy include the use of massage, which is applied by the therapist’s hands, by swirling water, or by mechanical devices; diathermy, which is the use of high-frequency electrical current; and hydrotherapy, in which the affected part is immersed in hot water. Exercise, electrical currents, and functional training are among the primary methods of physical therapy. Functional training includes the training of patients to use such devices as braces and artificial limbs. Occupational Therapy

The use of self-care, work and play activities to increase independent function and prevent disability is occupational therapy. It is used as an aid in recovery from physical or mental illness to create new habits and to maintain function. Occupational therapy is frequently used as a part of treatment after the acute phase of an illness has passed and may include adaptation of task or environment to achieve maximum independence and to enhance quality of life. Occupational therapists coordinate their treatment with the work of doctors, nurses, psychiatrists, and others. Many occupational-therapy departments have facilities in which the patient may be trained in the use of tools for trades, light industrial work, or clerical duties. Helping patients who have been hospitalized or unemployed for long periods of time to confront and solve the problems of daily life is a major focus of occupational therapy. Speech Therapy

Speech disorders can be caused by physical malformations, diseases, injuries, or psychological disorders. These problems are treated by the appropriate specialist. A cleft palate, for example, is a malformation that can be repaired by plastic surgery. Cases of childhood emotional disturbances or early schizophrenia are increasingly being recognized by speech pathologists, psychotherapists, pediatricians, and others. The speech therapist works with the patient to develop or improve communication skills: speaking, reading, and writing techniques. Respiration Therapy

Respiration therapy is a medical specialty that is primarily concerned with administering anesthesia and aiding breathing. A condition frequently managed by this therapy is an obstruction of the breathing passages. Therapy may consist of clearing the airway of mucus or liquid secretion by the use of suction. Respiration therapy may involve the use of gases, including those used for anesthesia during surgery. Psychotherapy

Treatment for psychological or emotional disorders is termed psychotherapy. It involves the formation of a relationship between a trained person and one or more patients for the purpose of changing or eliminating existing symptoms and for promoting personality growth. Drugs may be used as part of the treatment. However, the healing process is determined primarily by the verbal and nonverbal communication that is established between the patient or group and the therapist (seepsychology).

Both individual and group methods are used to treat the many disorders in which emotional factors are involved. These include behavioral disorders of children and adults; emotional reactions to the hardships or crises of life; psychoses, which are characterized by deranged thinking and behavior and often require hospitalization; psychoneuroses, which are chronic disorders that affect a person’s ability to function and that may be

accompanied by bodily symptoms; drug addictions; alcoholism; psychosomatic disorders, such as gastric or duodenal ulcer and certain skin diseases; and stress. Since low morale can contribute to the degree of disablement of all chronically ill or handicapped persons, psychotherapeutic techniques are a part of many rehabilitation programs.

Therapy that is directed toward a patient’s emotional growth emphasizes the development of insight into the individual’s feelings and behavior. This is ideally achieved by the development of a relationship in which the patient is allowed to express himself freely, while the therapist maintains a consistent and objective involvement. By feeling understood and accepted by someone whom he respects and trusts, the patient gradually reveals inner feelings about which he may have previously been unaware.

There are wide variations in the techniques used by psychotherapists. There is no convincing evidence that one form of psychotherapy is more successful than another. The personal qualities of the therapist and the patient’s capacity to become involved in the relationship seem to be important factors in the success of the therapy.

Psychodrama is a group psychotherapeutic method in which patients dramatize their personal problems before an audience of fellow patients and therapists. Art, music, and dance therapy are similar creative techniques in which patients are encouraged to express their feelings as part of therapy.

William A. Check

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vaccine

In 1921 there were 206,939 cases of diphtheria reported in the United States, mostly among children. In 1983 only five people came down with the disease. In 1941 measles claimed 894,134 victims; in 1983 there were only 1,497 cases. The main reason for the dramatic decline in these serious diseases has been the development and use of vaccines.

The DPT vaccine, which protects against diphtheria, pertussis, and tetanus, is routinely given to…

Amanda Mills/Centers for Disease Control and Prevention (CDC)

The immunologist Ian Frazer prepares to administer the vaccine Gardasil in 2006. His research led to …

In the United States, mass vaccination programs carried out against diphtheria, polio, and measles…

Encyclopædia Britannica, Inc.

A vaccine is a substance administered to humans or animals to protect them from serious diseases. The process of administering a vaccine is called vaccination. The process of protecting a person or animal from diseases is called immunization. Through the use of vaccines, humanity has been able to protect itself against many deadly and crippling diseases. Researchers are working to develop new vaccines against other health threats such as AIDS (Acquired Immune Deficiency Syndrome).

The first vaccine was developed by the English physician Edward Jenner in 1796 to protect against smallpox, a disease that disfigured and killed thousands of people each year. Jenner knew that dairy workers who caught the mild disease cowpox did not get smallpox. Jenner took material from a cowpox sore and scratched it into the arm of a healthy 8-year-old boy. As expected, the child developed cowpox. Jenner then scratched material from a smallpox sore into the boy’s arm. The child remained healthy. Jenner named the material from the cowpox sore vaccine, and the process in which he used it, vaccination. Both words are from the Latin vaccinus, meaning “from cows.” Use of the vaccine spread quickly; within 200 years smallpox had been eliminated from the world.

Vaccines are now available for a variety of diseases. The list is likely to grow as new techniques are used to develop safer, less costly vaccines.

Vaccines are used for several purposes. Their widest use is to immunize large groups of people or animals against serious diseases common in areas where they live. Travelers often receive vaccines to protect them from diseases found in the countries they will be visiting. A third use of vaccines is to protect high-risk groups, such as the elderly and the very young, who are at greater risk should they contract a contagious disease. How Vaccines Work

Learn about the basic strategies behind the use of vaccines to prepare the human immune system to…

The principle of vaccination is to cause the immune system to behave as if the body has contracted a disease. This sets in motion the body’s defense system without risking the damage that may be caused by the disease itself. Immunization can be either active or passive.

In active immunization, the components of the vaccine teach the individual’s immune system to recognize a specific toxin, virus, or bacteria. Each pathogen, or disease-causing agent, is identified by antigens, or marker molecules, on its surface. The immune system has cells called B-lymphocytes that detect these antigens and respond by manufacturing molecules called antibodies. Each antibody is made specifically to attack one type of antigen. The antibody combines with the antigen—like a key fitting a lock—and enables the immune system to destroy it. If the same type of pathogen enters the body again in the future, its antigens will be recognized, specific antibodies will be rapidly manufactured, and the organism that could cause a disease will be destroyed.

The protection against specific diseases conferred by active immunization generally lasts for years. If the antibodies formed after a vaccination decrease significantly over time, the individual can be revaccinated. So- called booster shots cause antibodies to be formed more quickly than they are by the first shot.

Passive immunization involves injecting antibodies made by one person or animal into the bloodstream of another. This type of immunization may be used if active immunization is not available; if an individual has already been exposed to a disease and does not have time to manufacture antibodies; or if an individual’s own immune system is not working properly. Passive immunization protects an individual for only a few weeks or months.

A nurse gives a patient a shot to vaccinate him against influenza.

Tim Boyle—Getty Images/Thinkstock

There are still many diseases for which it has not been possible to create vaccines. In some cases, this is because of the complexity of the pathogen. Other diseases, such as influenza, are caused by organisms that have the ability to change their antigens from time to time. A new influenza vaccine must be prepared each year to protect against the forms of the flu viruses that researchers predict will strike the population during the flu season.

A third category of organisms has the capacity to hide from the immune system. Some members of the herpes virus family, which cause cold sores, genital sores, shingles, chicken pox, and mononucleosis, live in nerve roots where they can avoid detection by the blood-borne B-lymphocytes. The body’s immune system cannot distinguish between the nerve root and the pathogen.

Technical problems have also hindered the development of vaccines. Research is expensive. Vaccines have side effects that can be quite serious for some individuals. Drug companies may be reluctant to produce vaccines because of the threat of lawsuits from those who may be harmed by these side effects. Even many existing

vaccines have not been widely used in developing countries because of problems with storing and administering the doses. Administration and Side Effects

A nurse administers a vaccine into the shoulder muscle of a 13-year-old boy.

James Gathany/Centers for Disease Control and Prevention (CDC)

Many vaccines can be given only by injection, because passage through the gastrointestinal tract would destroy them. The vaccine may be injected into a muscle, or intramuscularly; beneath the skin, or subcutaneously; or between the skin layers, or intradermally. Some vaccines are effective when given orally, such as the Sabin polio vaccine, and some are sprayed into the nose or mouth.

Vaccines made with live organisms generally need be given only once to confer lifelong immunity. Vaccines made from inactivated or killed organisms or toxoids, substances from disease-causing organisms that have been treated so as to induce formation of antibodies when injected into a person, often must be given several times to stimulate an immune response. Even then antibody production may decline after a time, leaving the individual vulnerable to the disease again. Booster shots may be required at regular intervals to raise immunity to protective levels. For instance, the diphtheria and tetanus immunizations are given initially at two-month intervals for a total of three doses. Immunity begins to decline after a few months, and booster shots are then administered periodically.

Not every individual will respond to vaccination by developing long-lasting immunity. Much depends on the person’s age, state of health, and ability to manufacture antibodies. Physicians believe, however, that if most of the population is immunized against common diseases, these illnesses will occur less frequently.

Adverse reactions, or side effects, have been reported for all existing vaccines. These reactions may range from a sore arm at the injection site to mild fever, joint pains, rash, or nausea, normally lasting only a short time. In extremely rare cases, however, severe reactions may occur.

Oral polio vaccines, in which live virus is used, have been known to cause mild to crippling paralysis in some people who received the vaccines. However, the incidence of serious problems is rare—approximately one case of paralytic polio per 9 million doses of vaccine. Vaccines are still among the safest and most beneficial preventive drugs available. Types of Vaccine

Until recently, vaccines have been made from naturally occurring viruses or bacteria or from the products of these pathogens. Vaccines may be prepared from live pathogens that have been weakened, or attenuated, in

some way. This technique prevents the pathogen from causing serious disease while still stimulating the immune system to produce antibodies. The antibodies formed against live pathogens last longer; however, the vaccine may not be as safe as one made from killed microorganisms. Vaccines made from weakened microorganisms include those for measles, mumps, rubella, and yellow fever.

The second type of vaccine may consist of dead viruses or bacteria. If the pathogens can be killed so that their chemical makeup changes very little, they will still cause the body to produce antibodies. While these vaccines are among the safest, the antibodies may not be as numerous as with live-pathogen vaccines and may not last very long. Diseases in which killed pathogens are used for the vaccine include typhoid fever, rabies, and whooping cough.

A third type of vaccine produces antibodies that fight against the poisons, or toxins, generated by pathogens. These vaccines contain chemically changed toxins, called toxoids, and are considered safe and highly effective. The diphtheria and tetanus vaccines are made in this manner.

Finally, some vaccines, like Jenner’s vaccine, consist of viral or bacterial particles that do not cause serious disease but resemble their disease-causing counterparts. These impostors can fool the immune system into producing antibodies against both diseases.

The advent of genetic engineering has enabled scientists to apply new techniques to the manufacture of vaccines. One approach is to use the recombinant DNA method to remove the disease-causing portion of a microbe without affecting its ability to stimulate antibody production. A recombinant vaccine against hepatitis B has been in common use since 1986. A second approach is simply to manufacture antigens artificially, without using any portion of the pathogen. Antigens are composed of building blocks called amino acids, assembled in a specific order. Scientists have learned how to string together amino acids in the proper order to elicit an antibody response without risking disease.

Genetic engineering has modified Jenner’s original vaccine, which was made from the vaccinia virus. This large and fast-growing organism can be changed, using the recombinant DNA method, so that it produces antigens against not one but a number of diseases. If successful, it could be the basis of a so-called supervaccine with a number of advantages. It would be cheap and easy to produce, because many countries have experience in producing the smallpox vaccine. It could be freeze-dried and thus easy to store without refrigeration; one inoculation could provide protection against many diseases; and administration of the supervaccine, like the smallpox vaccine, would leave a small scar, identifying protected individuals without requiring written records.

The new genetic techniques may provide ways to create vaccines for previously resistant diseases, such as malaria and herpes viruses, and perhaps for noninfectious diseases, such as those caused by parasites.

History of Vaccines

Edward Jenner, the discoverer of the smallpox vaccination, inoculates his child against the disease.

Wellcome Library, London (CC BY 4.0)

Louis Pasteur.

National Library of Medicine, Bethesda, Maryland

When Jenner performed his historic vaccination in 1796, he did not know why the process prevented smallpox. It was left to other scientists to discover the mechanisms of infection and immunity. Over the next 100 years, Robert Koch, a German physician, and others demonstrated that disease was caused by microbes. In 1879 French chemist Louis Pasteur was growing the microbes that caused fowl cholera. He left the cultures in his laboratory while he went on vacation. On his return, he injected some chickens with the old cultures and found

that they became only slightly ill. Furthermore, on recovery, they were immune to fowl cholera. He named his attenuated culture vaccine in honor of Jenner. Pasteur eventually developed an effective vaccine against rabies. The French scientist was the first to apply scientific principles to the manufacture of vaccines.

After Pasteur published his findings, other researchers began to develop vaccines. In the late 19th century, Émile Roux, a student of Pasteur, and Emil von Behring, a German physician, found that the killer in diphtheria was not the disease microbe itself but a toxin it produced. They laid the groundwork for the tetanus and diphtheria toxoid vaccines in the early 20th century.

In the 1950s American physician and researcher Jonas Salk developed a vaccine to combat…

Encyclopædia Britannica, Inc.

Wilhelm Kolle, a German bacteriologist, developed the typhoid and cholera vaccines in 1896. His method employed killed organisms that nonetheless were able to stimulate an immune response and to protect against disease. In the mid-20th century, Jonas Salk, an American physician, used the techniques of culturing viruses in living tissue in the laboratory to produce a vaccine against poliomyelitis. The polio vaccine, licensed in 1955, has virtually ended a disease that once killed or crippled thousands of children around the world each year. In the future the names of genetic engineers will undoubtedly be added to the list of those who have made significant contributions to the prevention of disease through the use of vaccines.

Diane E. JudgeEd.

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rickets: children with rickets

Britannica Note:

Noninfectious diseases have a wide range of causes, such as substances in the environment (silicosis and black lung), diet deficiencies (rickets and scurvy), disorders of the body’s immune system (lupus), or inheritable genetic defects (Tay-Sachs disease).

A diet deficient in vitamin D, calcium, or phosphorus, can result in rickets. The disease, which most commonly strikes children, causes bone deformities such as bowlegs.

Robin Laurance—Impact Photos/Imagestate

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epidemic

Women in Taiwan wear face masks to protect themselves from getting an illness called SARS. A SARS epidemic began in Asia in 2002. An epidemic is an outbreak of a disease that quickly infects a large number of people.

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virus: invasion of a cell

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Infectious diseases are caused by living organisms such as bacteria, fungi, protozoans, viruses, and parasites.

The process by which a virus invades a cell and reproduces.

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human disease: patient having blood pressure taken

The routine monitoring of blood pressure levels is an important part of assessing an individual's health. Blood pressure provides information about the amount of blood in circulation and about heart function and thus is an important indicator of disease.

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diabetes

Video Transcript

People with diabetes mellitus often check the amount of sugar in their blood. If it is too high they need more insulin. Insulin is a hormone that controls the level of blood sugar. In people with diabetes the pancreas may not make enough insulin or the body may not use its insulin properly. Diabetes patients receive the insulin they need through a shot or a pump. Doctors learned how to deliver insulin to patients in the 1920s. Before that, people with diabetes did not live long with the disease.

Insulin controls the level of sugar in the blood.

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Learn about dengue fever and how NS1 viral protein makes dengue a severe disease by causing vascular leak and shock

Video Transcript

Dengue is a mosquito-borne viral illness. And it's a huge problem these days, because it affects up to one-half of the world's population. Of the 390 million people who are infected every year, about 100 million can go on to develop what's called breakbone fever because of the severe pain and muscle and bone aches. I've actually had it, so I survived. But the problem is that several hundred thousand of the 100 million cases will continue on to severe disease, which can then be fatal within 24 to 48 hours. When a mosquito infects a person with dengue virus, it enters the bloodstream and then infects white blood cells. This then leads to production of more viruses. But only one viral protein is released from infected cells and this is called NS1. What we have now found is that this NS1 protein by itself can cause vascular leak, which means fluids escaping from your bloodstream that leads to then shock and potentially death. The disease causes vascular leak. Thus, we think this is too much of a coincidence. And we feel that NS1 now should be considered as part of the causal factors in dengue severe disease. One, it's compatible with what we've always known about severe dengue disease, which is that it's a result of what we call a cytokine storm, an excessive release of inflammatory immune molecules. And we've now shown that NS1 can directly cause the release of these inflammatory immune molecules, leading thus to vascular leak. The second aspect is that we've found that NS1 can cause leakage directly on the endothelial cells in the lung, meaning those cells that line the blood vessels in the lung. So dengue is a very difficult disease and needs to be attacked on many different fronts. Some of our work, for instance in Nicaragua, is directly in communities, stopping mosquito transmission. However, our work here at Berkeley focuses on upstream targets. And we're really excited that this new discovery can lead to additional targets for drugs, as well as new vaccines that can stop dengue in the future.

The dengue NS1 protein is thought to play a critical role in severe dengue disease by triggering immune reactions associated with vascular leak and shock, which are the major causes of death in persons suffering from dengue hemorrhagic fever.

Citation (MLA style):

Learn about dengue fever and how NS1 viral protein makes dengue a severe disease by causing vascular leak and shock. Video. Britannica LaunchPacks: The Treatment and Prevention of Disease, Encyclopædia Britannica, 19 Feb. 2021. packs-preview.eb.com. Accessed 10 Aug. 2021.

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