I would suppose if the BC is never cleaned and disinfected it could be possible. I clean mine and disinfect it. You can always roll it or squish it if concerned that you have animals running around inside of your BC bladder. I think we are all suffering from post pandamonium germaphobia.I'd be curious as to whether deliberately sucking air out of a BCD bladder into your lungs is a substantial risk, or no big deal?