Why are bats the litmus test for rabies, then? That just seems a bit odd. And why is rabies so prevalent/dangerous in bats that even breathing the air in bat caves can get you the disease?
For reference, there are two possible cases of this.
Two.
This is not a common thing.
I'm not sure this is actually the case for bats, but assuming your statement is true, it seems to be evidence for the presence of super-immunity, rather than against.