Lesson Overview

1. Lesson Overview 35.3 Fighting Infectious Disease

2. THINK ABOUT IT • More than 200 years ago, English physician Edward Jenner noted that milkmaids who contracted a mild disease called cowpox didn’t develop smallpox. • At the time, smallpox was a widespread disease that killed many people. • Could people be protected from smallpox by deliberately infecting them with cowpox?

3. Acquired Immunity • How do vaccines and externally produced antibodies fight disease?

4. Acquired Immunity • How do vaccines and externally produced antibodies fight disease? • A vaccine stimulates the immune system with an antigen. The immune • system produces memory B cells and memory T cells that quicken and • strengthen the body’s response to repeated infection. • Antibodies produced against a pathogen by other individuals or animals • can be used to produce temporary immunity.

5. Acquired Immunity • Dr. Edward Jenner performed an experiment in which he put fluid from a cowpox patient’s sore into a small cut he made on the arm of a young boy named James Phipps. As expected, James developed mild cowpox. • Two months later, Jenner injected James with fluid from a smallpox infection. The boy didn’t develop smallpox. • The boy’s cowpox infection had protected him from smallpox infection.

6. Acquired Immunity • The injection of a weakened form of a pathogen, or of a similar but less dangerous pathogen, to produce immunity is known as a vaccination. • The term comes from the Latin word vacca, meaning “cow,” as a reminder of Jenner’s work.

7. Active Immunity • Active immunity may develop as a result of natural exposure to an antigen (fighting an infection) or from deliberate exposure to the antigen (through a vaccine). • Vaccination stimulates the immune system with an antigen. • The immune system produces memory B cells and memory T cells that quicken and strengthen the body’s response to repeated infection.

8. Passive Immunity • Antibodies produced against a pathogen by other individuals or animals can be used to produce temporary immunity. If externally produced antibodies are introduced into a person’s blood, the result is passive immunity. • Passive immunity lasts only a short time because the immune system eventually destroys the foreign antibodies.

9. Passive Immunity • Passive immunity can occur naturally or by deliberate exposure. • Natural passive immunity occurs when antibodies are passed from a pregnant woman to her fetus (across the placenta), or to an infant through breast milk. • For some diseases, antibodies from humans or animals can be injected into an individual. • For example, people who have been bitten by rabid animals are injected with antibodies for the rabies virus.

10. Public Health and Medications • How do public health measures and medications fight disease?

11. Public Health and Medications • How do public health measures and medications fight disease? • Public health measures help prevent disease by monitoring and regulating • food and water supplies, promoting vaccination, and promoting ways that • avoid infection. • Antibiotics can kill bacteria, and some antiviral medications can slow down • viral activity.

12. Public Health and Medications • In 1900, more than 30 percent of deaths in the United States were caused by infectious disease. • In 2005, less than 5 percent of deaths were caused by infectious disease. • Two factors that contributed to this change are public health measures and the development of medications.

13. Public Health Measures • In 1854, Dr. John Snow learned, through interviewing residents and mapping, that the source of a London cholera outbreak was a water pump. This is a major event in the history of public health. • The field of public health offers services and advice that help provide healthy conditions.

14. Public Health Measures • Promoting childhood vaccinations and providing clean drinking water are two important public health measures that have greatly reduced the spread of infectious disease.

15. Medications • Medications, such as antibiotics and antiviral drugs, are other weapons that can fight pathogens. • An antibioticis a compound that kills bacteria without harming its host. • In 1928, Alexander Fleming noticed that a mold, Penicillium notatum, seemed to produce something that inhibited bacterial growth. Research determined that this “something” was a compound Fleming named penicillin. • Researchers learned to mass-produce penicillin just in time for it to save thousands of World War II soldiers.

16. Medications • Antibiotics have no effect on viruses. • However, antiviral drugs have been developed to fight certain viral infections. • These drugs generally inhibit the ability of viruses to invade cells or to multiply once inside cells.

17. New and Re-Emerging Diseases • Why have patterns of infectious diseases changed?

18. New and Re-Emerging Diseases • Why have patterns of infectious diseases changed? • Two major reasons for the emergence of new diseases are the ongoing • merging of human and animal habitats and the increase in the exotic • animal trade. • Misuse of medications has led to the re-emergence of diseases that many • people thought were under control.

19. New and Re-Emerging Diseases • By 1980, many people thought that medicine had conquered infectious disease. • Vaccination and other public health measures had wiped out polio in the United States and had eliminated smallpox globally. • Antibiotics seemed to have bacterial diseases under control. • Some exotic diseases remained in the tropics, but researchers were confident that epidemics would soon be history.

20. New and Re-Emerging Diseases • In recent decades, a host of new diseases have appeared, including AIDS, SARS, hantavirus, monkeypox, West Nile virus, Ebola, and avian influenza (“bird flu”). • Other diseases that people thought were under control are re-emerging as a threat and spreading to new areas.

21. Changing Interactions With Animals • Pathogens are also evolving in ways that enable them to infect different hosts. • As people clear new areas of land and as environments change, people come in contact with different pathogens.

22. Changing Interactions With Animals • Exotic animal trade, for pets and food, has also given pathogens new opportunities to jump from animals to humans. • In 2003, dormice from Ghana spread monkeypox to prairie dogs in the United States, which then infected humans. • The spread of SARS also has been associated with the wild animal trade.

23. Misuse of Medications • Misuse of medications has led to the re-emergence of diseases that many people thought were under control. • For example, many strains of the pathogens that cause tuberculosis and malaria are evolving resistance to a wide variety of antibiotics and other medications. • In addition, diseases such as measles are making a comeback because some people fail to follow vaccination recommendations.