Bat immune system is really special, highly dependent on interferons that blocks viruses genes from replacating instead of a more standard mammal immune system.

They need this because of their very fast metabolism needed to power flight. If that was not the case, their immune system would go haywire and kill them quickly.

This all good however it has drawbacks, like making them vulnerable to fungi and making them a perfect incubator for all kind of viruses.

Those new viruses then can cross species create real great problems.

There is a reason why Covid is thought to have originated in bats.