Bats have a pretty bad reputation, which is not surprising considering the number of pathogens they carry that can infect humans. Rabies, Nipah, Hendra, Ebola and Marburg are all viruses carried by bats that can cause serious disease in humans. Marburg virus and some strains of Ebola virus can kill up to 80-90% of humans infected. Furthermore, most of these are emerging diseases that have rudely burst onto the scene over the past 50 years (although some argue they have been around a lot longer, but weren't diagnosed). But what is causing this rise in viral disease? It turns out that it is just as much their fault as it is ours.
Humans have started creeping into bat territory, especially in the tropics, which has led to an increased risk of contact with these animals. For example, in Malaysia, commercial pig farms were installed in bat inhabited forests which consequently led to the first human outbreak of Nipah, via pigs.
However, it seems that bats also carry more human pathogens than other animals. Why is this? Bats like to live close to one another, snuggling up as they roost, giving plenty of opportunity for pathogens to spread between the bats.
So why don’t these nasty viruses kill off the bats? Scientists think it’s actually thanks to their ability to fly. Flight is hugely costly energy wise, and when a lot of energy is used a lot of waste is consequently produced. To prevent this reactive waste from damaging the bats’ DNA, bats have evolved sophisticated defence mechanisms that conveniently also help to prevent the bats from succumbing to disease.
Now you may be thinking- how do the viruses survive in the bats, then? Once again it’s back to flight. Viruses are totally dependent on the host to replicate, unlike bacteria, and consequently they require quite specific conditions. When bats fly, their internal temperatures are ramped up to around 40oC (104oF), which is too hot for many viruses. This will kill off a lot of the viruses in the bats, leaving only those hardy viruses that have evolved tolerance mechanisms. Unfortunately for us, this also means they can tolerate a burning human fever.
But don’t go hating on bats because of this- they’re incredibly important pollinators and they also eat mosquitoes. You win some, you lose some.
Check out this video to find out more:
[Header image "Short nosed fruit bat approaching figs," by Natasha Mhatre, via Flickr, used in accordance with CC BY-NC-SA 2.0]