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Why diseases spread.

Every year, cases of the cold and flu seem to spread widely across the U.S. During the 1940s and 1950s, for example, polio was a national epidemic. Just how do diseases spread so rapidly?

According to Stan Silberg, an epidemiologist at the University of Oklahoma Health Sciences Center, methods include infectious droplets entering and leaving through the respiratory tract; agents of disease contaminating water, food, or milk and entering and leaving through the digestive system; sexual contact; and arthropod vectors such as mosquitoes, ticks, etc. The speed of the spread of infectious agents depends on the presence of a densely populated community, a highly susceptible population due to lack of immunizations, and insufficient medical care.

The rapid spread of diseases partially can be explained by modern transportation systems and the fact that people are traveling more than ever before. "Airplanes, especially, allow us to go from one end of the world to the other in a matter of hours. You can be incubating an organism--influenza, for instance--and, if you're on a crowded airplane, the people around you can get infected. Look at how many people are going to get off in various spots across the country. When they get off the plane, each individual has the potential of spreading the infecting agent to many others.

"Some of the most common communicable diseases--such as influenza, measles, tuberculosis, and common colds, as well as many others--are rapidly spread through the respiratory tract. Sexually transmitted diseases also are rapidly spread.... In addition to persons who are clinically ill from infections, there are those who are subclinically infected.' They may have mild signs and symptoms, but are not sick enough to keep them away from work or school where they can spread their infection further. Then there are the carriers who appear to be healthy and probably don't even know that they are carrying an infectious agent--yet they can be spreading their infection to others. That's why it's extremely difficult to control infectious diseases, because even people who aren't |clinically sick' are spreading the agent." Those that spread rapidly include sexually transmitted diseases such as AIDS, gonorrhea, and syphilis; waterborne types such as cholera and typhoid fever; and milkborne or foodborne outbreaks such as salmonellosis and hepatitis.

Silberg suggests that the best way to prevent getting a communicable disease is to make sure all available immunizations are taken and updated. "Infectious diseases are not dead--not by a long shot. We always think that we are completely safe, but we're not. The discovery in very recent years of . . . AIDS and Lyme Disease and other infectious agents are good examples. The only infectious disease that is considered to be eradicated, so far, is smallpox. Most of the infectious diseases are controlled, except for perhaps AIDS right now. The reason we don't have epidemics anymore is the implementation of established control measures, but if people become too complacent, epidemic diseases ca return."
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Publication:USA Today (Magazine)
Date:Feb 1, 1993
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