This is the exact reason why I never do bbbj. And I know I talk alot anout licking assholes, but truth be told, its only happens when I have a thin latex dental dam stretched over my face and tongue. 
I talk a lot about doing TUHA, but again, think of the possible infections I could get by sticking my tongue in and out of a chicks asshole. Thats gonna be covered too. True, Id get no taste at all, but to me, its just the fantasy of having my tongue up her ass as far as possible.
Moral of the story. Wrap it, cover it! Stick your dick or tongue in any hole available, just make sure its covered.
There are a lot of ladies with assholes that I want to tongue deep if they would let me, its just gonna be covered with that thin latex that I can put over my mouth. Its the only way to play safe for deep rimming. And I do like to go deep