You called in sick yesterday because you thought you had the flu, but today you feel even worse. You have heavy bleeding and delirium because you’ve got one of the world’s most deadly viruses. What ...

As they say, the difference between medicine and poison is the dose. The difference between viral transmission and infection, it appears, has to do with the restraint found in the virus itself.

Add Yahoo as a preferred source to see more of our stories on Google. Woman applying insect repellent against mosquito and tick on her leg during hike in nature. Skin protection against insect bite© ...