A virus that infects your brain, makes you want to bite things, and which is almost always fatal after symptoms appear probably sounds like something from a zombie movie. But this has been the modus operandi of rabies since at least 2300 BC, when it was described in the Eshuma Code of Babylon. The word's Sanskrit etymology - rabhas, meaning "to do violence" - dates back even further, to 3000 BC.

In principle, no human in this day and age should die from rabies, and yet, according to a 2015 study, canine rabies kills 59,000 people each year. That's 160 people every day, and the actual number is higher as cases go unreported. Most of these deaths occur in Asia and Africa, with India alone accounting for one-third of the world's total mortality from rabies.

That total is not as high as the death toll from tuberculosis, HIV/AIDS, and malaria; but, unlike those diseases, every mammal appears to be susceptible to rabies. Dogs, the predominant host in most regions, can become infected from any rabid wild animal, and then infect humans. Dogs showing symptoms may bite a human, but they can also transmit the virus simply by licking if their saliva comes into contact with a scratch, damaged skin, or mucous membrane.