Our domesticated cats get cat flu and flees if they don't get vaccination. There are diseases that only domesticated animals get. Cats in the wilderness don't even need vaccination.

I don't know about that (though a look at Wikipedia does say cat fleas are a problem for domesticated cats, without mentioning wild ones). There are plenty of diseases wild animals get, though; for example rabies, or canine distemper, which massacred the North Sea seal population in the late 1980s.