New and Re-Emerging Diseases

Why have patterns of infectious diseases changed?

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. Unfortunately, they were wrong.

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. What's going on?

FIGURE 35–16 Causes of Emerging Disease Illegally imported animals can lead to the spread of emerging disease. A. In 2003, dormice and other rodents from Africa spread monkeypox to prairie dogs in the United States, which then infected humans. B. The spread of SARS also has been associated with the wild animal trade.

Changing Interactions With Animals 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. As people clear new areas of land and as environments change, people come in contact with different animals and different pathogens. Exotic animal trade, for pets and food, has also given pathogens new opportunities to jump from animals to humans. Both monkeypox and SARS are thought to have started this way. Pathogens are also evolving in ways that enable them to infect different hosts.

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.

35.3 Assessment

Review Key Concepts

1. 1. Review Explain how vaccinations and externally produced antibodies help the immune system fight disease.

   2. Compare and Contrast Describe the difference between active and passive immunity.

2. 1. Review What are the goals of public health measures?

   2. Relate Cause and Effect Why is it important to discern if a sickness is caused by a bacterium or a virus?

3. 1. Review Describe two major contributing factors involved in the spread of new and re-emerging diseases.

   2. Infer How do you think the ease of global travel has affected the spread of emerging diseases? Explain.

Apply the Big idea

Science as a Way of Knowing

4. Getting vaccinated is much safer than getting the disease that the vaccine prevents. However, like any drug, vaccines are capable of causing side effects. As a class, arrange a debate that addresses both the benefits and risks of vaccinations. Debaters on both sides should use reliable sources to support their arguments.

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