Well, allow a career nurse's assistant to chime in.

Having wiped and washed asses for not a living (seriously, the pay is bad) for twenty years, I can 100% guarantee you that it does not matter how much you wash the ass, if there are worms in the intestines, you still run the risk of sucking a few of them up while you're hoovering the ass with your tongue.

And, even if you hose that thing down, the risk of bacterial transfer is non zero.

First, the ol' brown eye is wrinkly as hell. Washing your own ass means you can't see everything to be certain you got every last trace of fecal matter. That trace may be smaller than a pinhead, but when you're tongue-punching the fart box, that pinhead is still going to get licked up.

Second, it isn't like all the bacteria in the area magically disappear. Most people get so focused on the anus itself, they don't remember to scrub the cheeks. Maybe you're an exception to that, I dunno. But bacteria are fast spreading little bastards. Anything that's even remotely close will be back in under an hour.

And, even with hot, running water and soap, you can't guarantee 100% removal of all bacteria. Even with antimicrobial soaps and supplies, you're washing your ass blind, and it's wrinkly. So chances are that there are still small batches hiding in a wrinkle. A few minutes after drying off, and they're enjoying the hot, moist goodness of a gluteal crease, having a bacteria party and reproducing like, well, bacteria.

All of that ignores that as soon as you fart the first time, some amount of bacteria are coming out. Even without that, the anal sphincters (yes, there's multiple) aren't exactly airtight. Something microscopic is more than small enough to creep out.

So, scrub away as much as you like, but anyone eating your ass is still coming in contact with some amount of intestinal content, including but not limited to, feces, e-coli, and any worm eggs or worms present.