1. Section 21.4 Emerging Infectious Diseases Objectives
Define the term emerging disease.
Identify five reasons why diseases emerge.

2. Health Stats The map shows how dengue fever, a viral disease carried by mosquitoes, has spread since 1960.
Should the United States be concerned about dengue fever? Explain.

3. What Is an Emerging Disease?
An epidemic (ep uh DEM ik) is an unusually high occurrence of a disease in a certain place during a certain time period.
When an epidemic affects many areas of the world, it is sometimes called a pandemic.
An emerging disease is an infectious disease that has become increasingly common in humans within the last 20 years or threatens to become more common in the near future.

4. For: Updates on modern epidemics
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5. Why Do Diseases Emerge?
Diseases can emerge when humans come into contact with infected animals; pathogens become resistant to existing drugs; or people lack appropriate immunizations.
The increased frequency of international travel and a global food supply can enable emerging diseases to spread very quickly.

6. Contact With Infected Animals
Some diseases that are common in animals can spread to humans.
There have been recent cases in Asia in which people have become sick after being exposed to infected birds.
Scientists fear that another deadly flu epidemic could result if the virus takes on a form that can spread easily between people.

9. Drug Resistance
Some diseases are caused by pathogens that can mutate, or change, over time.
Sometimes these mutations result in a strain, or type, of pathogen that no longer responds to medicine.

10. Lack of Immunization
Diseases that were common many years ago can pose a threat again if people don’t get the proper immunizations.
The polio virus remains a threat in several Asian and African countries because many people in those countries have not received the vaccine.

11. International Travel
Globalization refers to the fact that people around the world are no longer geographically isolated from each other.
Not only can people travel much more easily, but so can any pathogens that live in their bodies.
World travelers could spread the pathogen around the world in a short amount of time.

12. Global Food Supply Food also travels around the world.
If a pathogen is present in a food product, it can spread quickly.

13. Vocabulary
epidemic
An unusually high occurrence of a disease in a certain place during a certain time period.
emerging disease
An infectious disease that has become more common within the last 20 years or threatens to become more common in the near future.

14. QuickTake Quiz
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15. For: Chapter 21 self test
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16. End of Section 21.4 Click on this slide to end this presentation.