TRY THIS activity Following an Infection

In this activity, you will simulate the spread of an infection. Each member of your class will be provided with a numbered plastic cup filled with a mystery fluid. One of these cups will contain an “infection.”

Safety goggles and a lab apron must be worn for the entire laboratory.

Materials: index card, numbered plastic cup of mystery fluid • Write your name and cup number on your index card. • Share your mystery fluid with a classmate. Pour all of your fluid into your partner’s cup. Then your partner pours half of the combined liquids back into your cup. Each partner then records the other’s cup number on his or her index card. • Repeat the previous step until each student has shared fluids with exactly three other students. • Once all exchanges have occurred, your teacher will add a drop of phenolphthalein indicator to each of the cups. A pink colour indicates an infection. (a) Can you identify the origin of the infection? (b) If so, then identify the source. If not, why not?

Case Study Disease Transmission Even before Louis Pasteur proposed the germ theory, a Hungarian physician, Ignaz Semmelweis (1818–65), made an important connection between sanitation and dis- ease. Semmelweis was distressed by the high death rate from childbed fever among women who gave birth to babies in hospitals in Vienna, while the death rate among women who gave birth at home was considerably lower. Suspicions were further peaked when it was discovered that a physician who had cut himself while dissecting a cadaver developed childbed fever, the same fever linked to the death of mothers who had given birth in hospitals. Semmelweis insisted that the doctors wash their hands with a solution of chlorinated lime before attending to women giving birth. Within a year, the death rate in maternity wards fell from 12% to 1.5%. However, many Austrian doctors were humiliated by the inference that they had been unwilling accomplices in the deaths of women in labour. Semmelweis was driven out of Vienna and returned to Budapest, where he again reduced the incidence of childbed fever. His recommendations were accepted in Hungary and the government instructed all district authorities to adopt his measures. Once again, Semmelweis encountered opposition from many prominent doctors. In 1865—the same year that English doctor Joseph Lister independently demonstrated how germs could be controlled by chemical agents—Semmelweis suffered a mental breakdown and was admitted to a mental institution where he soon died. One of the most famous cases of disease transmission involves a cook who worked for eight families in the state of New York in the early 1900s. Known as “Typhoid Mary,”this middle-aged woman showed no symptoms of typhoid but spread it to those who ate the food she prepared. Over a 10-year period, Mary Mallon was responsible for seven epi- demics that infected more than 50 people with typhoid fever. One estimate indicates that she may have been indirectly responsible for as many as 200 cases. Authorities first tracked her down in 1907 and isolated her in a cottage on an island. In 1910, she was released after agreeing not to take a food-handling job again, but she did, causing more

478 Chapter 10 NEL Section 10.4 typhoid outbreaks. The New York City health authorities found her again in 1915 working as a “Mrs. Brown” in a maternity hospital in New York, where she had infected another 25 people (of whom two died). She was sent back to the island and remained there for the remaining 23 years of her life. The carrier is the key link in the transmission of typhoid. The convalescent patient con- tinues to release both solid and fluid wastes containing the harmful microbe. The patho- genic microbe is transferred to food and finally to a new host. The bacteria then incubates in the new host, usually for 14 days, and then symptoms begin to appear. High fever is followed by chills. In most cases, typhoid fever causes mucus to build up in the respiratory tract. The patient experiences difficulty breathing and, in many cases, the disease produces rosy spots on the abdomen. The greatest damage that the microbe does is to the digestive tract; small holes or perforations in the small intestine often begin to bleed.

Case Study Questions Understanding Concepts 1. What might account for a higher death rate in hospitals? Where would you begin to look for the source of the problem? 2. In the Semmelweiss case study, what evidence suggests that the doctors themselves were transmitting childbed fever? 3. What was the source of the disease? 4. Speculate as to why Mary Mallon did not show any symptoms of typhoid. 5. Why are perforations to the intestine dangerous? 6. In the case of typhoid fever, how might the cycle of disease transmission be broken?

Discovery of Pathogens When someone comes down with a fever and chills, the first thing that person suspects is the flu. The comment you might hear is “Yes,I believe a new bug is making the rounds.” The person who made the comment may not know how a virus differs from bacteria but does have a general idea of what causes disease. Remarkable as it might seem, that is a great deal more than people once knew. Diseases were thought to be caused by foul air, evil spirits, or bad blood. A direct link between disease and microbes was not established until French chemist Louis Pasteur (Figure 5) began experimenting with yeast in 1854. Although many people suspected that invisible organisms cause disease, no one had proven the role of microbes. The earliest description of bacteria came from Dutch physicist Anton van Leeuwenhoek, the inventor of the microscope. Although van Leeuwenhoek described bacteria in 1683, Figure 5 he did not know what they were. French chemist and bacteriologist Louis Pasteur was interested in discovering why wine often went bad during the fer- Louis Pasteur (1822–95) proved that the fermentation process was mentation process. While studying wine under a microscope, Pasteur identified tiny round caused by a specific microbe. Best spheres suspended in the wine. The spheres, he discovered, were living yeast cells. As the known for introducing the process population of yeast cells grew, the amount of alcohol in the wine increased. How did the of pasteurization, Pasteur also presence of yeast affect the grape juice? Pasteur concluded that yeast cells produce alcohol. isolated the bacterium that causes The spoiled wine did not contain alcohol but another chemical, called lactic acid. anthrax and pioneered the vaccine When Pasteur looked at the spoiled wine under a microscope he found rod-shaped bac- against rabies. teria. He concluded that the rod-shaped bacteria were causing the wine to go bad. The microbe was the villain! It wasn’t long before Pasteur and other scientists began looking for the villainous microbe as the cause for human diseases. Pasteur’s discovery led to what has come to be

NEL The Maintenance of Balance by the Immune System 479