Bats are linked to many diseases, but most recently Covid-19. Bats are very susceptible to diseases because flying takes up so much of their energy. The stress that it puts on the bat is so great that the bats have evolved a different way of fighting diseases. They have a better way to repair cell damage and fight off viruses so that the bat doesn’t even show symptoms. That bat then transmits it to other species (which then transmit it to us) or straight to us via wet markets or us interacting with the bat in the wild or in labs.