PART I INTRODUCTION TO EMERGING INFECTIOUS DISEASES COPYRIGHTED MATERIAL CCH001.inddH001.indd 1 221/02/111/02/11 111:551:55 AAMM CCH001.inddH001.indd 2 221/02/111/02/11 111:551:55 AAMM CHAPTER 1 INFECTIOUS DISEASES PAST AND PRESENT LEARNING OBJECTIVES ● Discuss the roles of plague and smallpox in human history ● Discuss the most important infectious diseases in the world today ● Discuss the linkages between infectious diseases, poverty, and civil unrest ● Describe a number of emerging and reemerging infectious dis- eases found in the Americas, outside of the Americas, and throughout the world ● Discuss a number of factors contributing to the emergence or reemergence of infectious diseases ● Gain a sense of the number of new infectious diseases that have emerged recently and the rapid pace of discovery of the microbes responsible, development of antimicrobial drugs, and evolution of microbial drug resistance CCH001.inddH001.indd 3 221/02/111/02/11 111:551:55 AAMM 4 EMERGING INFECTIOUS DISEASES Major Concepts History Infectious diseases have had a great impact on human history, killing vast num- bers of persons and disabling or disfi guring many others. Some diseases have transformed the social and economic landscape of a region, as when the decline in the peasant population following the Black Death contributed to the end of the feudal system. The fi ght against smallpox led to the development of vaccina- tion, a weapon in the human arsenal that prevented major loss of life by protect- ing people from a wide range of diseases. Due to an ever-better understanding of the causative agents of infectious diseases, other tools have been developed to prevent or treat illnesses, including improved sanitation, greater availability of clean drinking water, the increased use of disinfectants, the discovery of antimicrobial compounds, and improvements in the inspection, processing, and preparation of food and drink. The incidence and severity of infectious diseases have fallen in developed nations but are again on the rise worldwide. Infectious Diseases Today The leading causes of death due to infectious diseases in the world today are lower respiratory tract infections, diarrheal diseases, HIV/AIDS, tuberculosis, malaria, and dengue hemorrhagic fever and shock syndrome. Many of the victims of these diseases belong to the most vulnerable segments of our population, the very young and the very old, those weakened by other pathological conditions, and those with compromised immune responses. Many other diseases affect smaller segments of humankind. Some of these preferentially strike those living in certain climates or ecosystems, in lower socioeconomic groups, or in regions of civil unrest and war. Other diseases are more prevalent in some racial groups, age ranges, occupations, or one gender. Still other diseases are indiscriminate killers. Incidence of some diseases peaks in certain seasons, while others occur year round. Emerging and Reemerging Infectious Diseases Many diseases have either been described for the fi rst time within the past 40 to 50 years or have increased in incidence, severity, or geographical range. This text focuses on a number of such diseases and the associated microbes. Several factors in combination have contributed to the explosion of emerging and reemerging infectious diseases in recent times (as evidenced by the Timeline at the end of this chapter). Our awareness of new infections may be due in part to improved CCH001.inddH001.indd 4 221/02/111/02/11 111:551:55 AAMM INFECTIOUS DISEASES PAST AND PRESENT 5 detection and understanding of the underlying causes of illness. Many of the emerging diseases, however, appear to be entirely new to humans, while many reemerging diseases represent increasing threats to humankind. Several of the fac- tors believed to contribute to the emergence or reemergence of infectious diseases include microbial evolution, the trend toward increasing urbanization, population migrations between regions or into formerly uninhabited areas, the ease and speed of long-distance movement of persons and materials, natural disasters, climatic and ecological changes, and decreased vaccination rates in many regions of the world. One of the important factors contributing to the rapid emergence of new infections is the increasingly large numbers of immunocompromised indi- viduals who are vulnerable to the development of severe or life-threatening diseases as a result of infection by organisms formerly viewed as nonpathogenic. History of Infectious Diseases Much of the history of humankind has been critically shaped by infectious diseases. Large, widespread outbreaks of bubonic, pneumonic, and septicemic plague, caused by infection with Yersinia pestis, have struck repeatedly, includ- ing the Plague of Justinian from 542 to 767, which killed 40 million people in Europe and Asia Minor and initiated the Dark Ages, and the Black Death, lasting from the fourteenth to eighteenth centuries. The latter began in Central Asia and subsequently spread to China, India, and Asia Minor, entering Italy in 1347. Twenty-fi ve to fi fty percent of the population of Europe succumbed to the plague within the next three years, leading to the death of many peasants and the abandonment of much of the agricultural land. The resulting food shortage and loss of an abundant workforce rendered the existing governments ineffective. These were major factors in the eventual collapse of the feudal system and the rise of middle-class artisans. Improvements in sanitation were also implemented due to lessons learned during the plague years. Smallpox is another disease that changed the face of human history, quite literally, for over three thousand years, affl icting humans with horrifi c and disfi g- uring scars, blindness, and death for most of our known existence. Its eradication has been one of our greatest achievements. The rich and powerful were not spared the attention of this deadly pesti- lence. Scars were even found on the mummy of the Egyptian pharaoh Ramses V. Throughout the ages, the fatality rate often approached 30%, with 65% to 80% of the survivors left with pockmarks on their faces as reminders of their ordeal. As late as the 1700s, 10% to 14% of the children in France, Sweden, and Russia died of smallpox. Surviving the disease was almost a rite of passage, and no parent could be totally at ease until his or her children had vanquished that most dreaded foe. CCH001.inddH001.indd 5 221/02/111/02/11 111:551:55 AAMM 6 EMERGING INFECTIOUS DISEASES FIGURE 1.1 Child with smallpox Source: CDC/Jean Roy. “The smallpox was always present,” wrote T. B. Macaulay, “fi lling the churchyards with corpses, tormenting with constant fears all whom it had stricken, leaving on those whose lives it spared the hideous traces of its power, turning the babe into a changeling at which the mother shuddered, and making the eyes and cheeks of the betrothed maiden objects of horror to the lover.” It was observed in China over a thousand years ago that survivors of smallpox did not contract the disease again, even after extended exposure to infected per- sons. It was additionally discovered that inoculation of previously unexposed persons with material from dried smallpox scabs derived from persons with mild cases of the disease often safeguarded the inoculated persons against developing severe infection at a later time. This practice was known as variolation and occasionally resulted in death. Variolation was brought to Europe in 1721 by Lady Mary Wortley Montagu, the wife of the British ambassador to Turkey. Decades later, Edward Jenner acted on the common observation that milkmaids, who typically developed the mild disease cowpox, did not later suffer from smallpox or develop the hideous scars present on most members of society. In 1796, he modifi ed the practice of variolation by inoculating a young boy, James Phipps, with material from cowpox scabs and subsequently challenging him with smallpox. Fortunately for James (and humanity), the boy was protected. Thus began the age of vaccination, which ultimately led to the eradication of smallpox as a result of the concerted efforts of many dedicated individuals work- ing under diffi cult conditions throughout the world for a decade. The program featured the quarantine of patients and their contacts as well as vaccination of all CCH001.inddH001.indd 6 221/02/111/02/11 111:551:55 AAMM INFECTIOUS DISEASES PAST AND PRESENT 7 FIGURE 1.2 Sign announcing smallpox vaccination Source: CDC. potential contacts. Ali Maalin from Somalia is believed to have acquired the last naturally occurring case of smallpox in 1977. Several subsequent cases occurred several years later in England following viral escape from a laboratory. While smallpox remains the only disease that humans have totally eliminated from nature, the lessons learned during this triumph of humans over one of its most deadly foes have been applied many times in subsequent years. Highly effective vaccines have been developed and brought into widespread use to tame other serious microbial diseases such as polio, whooping cough, German measles, mumps, and tetanus. The science of epidemiology, initiated by John Snow to trace the source of a cholera epidemic in London in the 1850s to a specifi c water pump, transformed public health. The “germ theory of disease,” developed by Louis Pasteur, Robert Koch, John Lister, and others in the 1860s, revolution- ized beliefs concerning the origins of diseases. These developments—along with improvements in sanitation, the availability of clean drinking water, practices such as pasteurization and sterilization of beverages and food, increased use of disinfectants, the discovery of antimicrobial compounds such as antibiotics (discussed in Chapter Eleven) and antiviral drugs, improvement in the inspection of meat and processing facilities, more thorough cooking of meat and eggs, and educational programs—eventually served as tipping points for many infectious diseases in the developed areas of the world. The numbers of cases of microbial illnesses dramatically declined: the incidence of tuberculosis, malaria, cholera, and many other diseases fell either regionally or around the world.