how can bats be hosts to a range of deadly viruses without getting sick?
In: Biology
Bats are very social animals – they live in huge colonies so it’s easy for viruses to spread between them. Over a very long time, evolution has selected for the adaptations that lets them tolerate these viruses. They evolved a much less destructive immune system than humans and other mammals. In humans, when we encounter a virus, our immune system is what actually causes us to feel so crummy. It’s *our body* that raises our temperature, makes our noses run, gives us a horrid cough, etc.
Bats have an immune system that doesn’t respond as strongly when it sees a virus, and when it does respond, it’s limited to just destroying the things it needs to. It doesn’t trigger such extreme inflammation as you see in humans, and what inflammation does happen, the bat has some other adaptations that helps limit it.
Humans have a similar ability but only in specific parts of our bodies – our eyes for example. When you get an eye infection, unless its very severe, you have a special immune response that keeps everything under much more control so as to avoid you going blind.
It’s not without it’s downsides though. Bats, while very good at tolerating intracellular pathogens like viruses, don’t seem to be as good when it comes to extracellular pathogens like bacteria and fungi. Very sadly, many populations of bats have completely collapsed due to a fungus *Pseudogymnoascus destructans* which causes white nose disease.
Their immune system also isn’t completely immune to viruses. Rabies, for example, is very lethal in bats.
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