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Name: Denise Scherer
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Why are scientists finding new infectious diseases?

Two possible sources of new diseases come to my mind: first, not all diseases have been recognized as such yet. That is, not all of the existing microbes that infect us have yet been identified and linked to some set of symptoms. It's not easy to decipher from among the constellation of daily complaints the body makes a certain small set of symptoms and realize they're related to some infection. For example, AIDS was only recognized as a disease in about 1981, but now, with the advantage of hindsight and knowing what to look for, people have been identified as having died of the disease as far back as 1959, I believe.

Second, bacteria evolve very rapidly, with new strains and species possible on a time scale of years instead of millennia. Thus entirely new strains and species evolve to plague us. This is the case for the regular epidemics of influenza, for example. Also, "partial" cures using antibiotics by humans help this along. When you take antibiotics, enough to feel better, say, but not enough to actually wipe out every last microbe, then what you are doing is weeding out the least drug-resistant microbes. The ones that escape start a new more drug-resistant strain. This (un)natural selection is widely blamed for the recent growth in cases of multiply-drug-resistant tuberculosis.

Christopher Grayce

A good answer, that first one. Let me add a bit more. With the increase in world-wide mobility, (air travel, etc), people are going to places and encountering infectious agents that their ancestors have never encountered. Sometimes this means that a disease is evident in a population where it never was before; and so it gets recognized. Furthermore, occasionally diseases will cross species lines (several viruses are known to have done this) leading to a "new" human disease.

Steve J Triezenberg

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