Out of all the germs and viruses, which one is the most feared?

These days, they are most likely AIDS followed by MRSA (Methicillin Resistant Staph Aureus).

But it depends on where you ask in history. In the 1940's and 1950's, it was Polio. Earlier in the 1900's, it was tuberculosis. In the middle ages it was Yersinia pestis — the Black Death.

Pretty much, and infection that’s difficult to treat, and that causes a prolonged disease followed by death, becomes the most feared bacteria or virus.

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Answer:
There are way too many to state there's a “most” feared one. My personal fear is the bacteria that causes necrotizing fasciitis (flesh-eating disease). It's caused by the same bacteria that causes strep throat. Scary. Seeing as how we're not a third world country, somehow ebola and the plague scare me less than that.

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Answer:
This is subjective, but I guess with movies and books out about Ebola and other hemmorhagic fevers and its capability to rapidly kill and lack of treatment. This may be most feared.

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Answer:
AIDS.