Why do microbes need a live host?

Anthony L. Komaroff, MD
Internal Medicine
Not every microbe that enters your body will make you sick. But when one does, you may be reassured to know that it's not in the germ's best interest to kill you. It needs you alive, at least for a while, so it can continue to thrive, reproduce, and spread to other people.

Take, for example, human immunodeficiency virus (HIV), the virus that causes acquired immune deficiency syndrome (AIDS). The fact that it takes a long time to kill the people it infects is an example of how some viruses work slowly within the body. Most HIV-infected people don't know they are infected and contagious until they start to feel sick, which is usually years after they are infected. In the meantime, people who don't know they have the virus can spread it to other people through sexual contact or other means. In one sense, this strategy benefits not only the human host, who survives for years after initial infection, but also the virus, which has plenty of time to spread to other humans.

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