Ebola, rabies, SARS, Nipah, and MERS-CoV all have something in common. They are all viruses, spread by bats, that often cause lethal disease in humans—the 2014-2015 Ebola outbreak killed over 11,000 people1—yet they don't sicken or kill their bat hosts. When animals efficiently transmits disease for long periods of time in the absence of disease themselves, they are known as reservoirs.

So what is it about bats that allow them to act as reservoirs for over 60 human pathogens? This question has plagued the scientific community for decades, starting with the discovery of bats as the reservoir for rabies virus in 1932 and continuing today with the recent Ebola outbreak and the ongoing search for novel viruses that may cause the next pandemic2. Part of my work focuses on this – digging in to the genome of these new viruses to investigate how closely related they may be to known viruses that infect humans.

A number of lifestyle factors make bats unique which may help explain their seeming resistance to pathogens causing significant illness and death across human populations. Above all, it is unusual for a mammal to use powered flight and hibernate in high densities like bats do with other species. They are also remarkably long-lived compared to other mammals of their size (10-20 years compared to a rat’s average of two years).

Other characteristics sometimes shared by other mammals but potentially increasing bats’ potential to act as a reservoir for these pathogens include their gregarious social behavior and mutual grooming patterns, ability to travel long distances, nocturnal activity, and broad species diversity (the second highest after rodents). This handful of unique characteristics makes bats difficult to study in controlled laboratory environments and has caused obstacles in obtaining information on why these animals are so efficient at transmitting lethal diseases to humans.

Here are a few theories scientists have on how bats transmit disease without becoming sick themselves.

http://blogs.scientificamerican.com/guest-blog/why-don-t-bats-get-ebola/