Why humans keep getting viruses from bats

Republishing an old essay

Originally from March 2020. Try to guess why I was writing about this then!

Humans get a surprising number of very infectious diseases from bats. We get SARS (including the recent COVID-19/SARS-CoV2), Ebola, rabies, and possibly mumps. These are all incredibly infectious, deadly diseases.

This seems weird because human beings aren’t in particularly close contact with bats. They’re nocturnal, don’t have large city populations (for the most part), and humans don’t eat them that often. It should be harder for diseases to pass from them to us. They’re also not very similar to us genetically, so their diseases shouldn’t be able to leap to us so easily.

Part of the answer is that bats are very social creatures. When one bat gets a virus, they pretty quickly pass it onto the other bats in their colony. However, that’s also true of goats and cows, who don’t seem to pass on infectious diseases to us as often.

The more important part of the answer is that bats are “reservoirs” of some particularly virulent viruses. Bats live with long-term infections of SARS or Ebola and are seemingly ok with it. While humans and other mammals either have to clear these viruses from their body or die, bats do not. They will just keep on keeping on, sometimes shedding the virus, sometimes not. It’s more likely that the bat will shed the virus during stressful times (i.e. when it’s in a cage and about to get eaten).