Never had any adverse effects from getting bitten by Houdini, but he's never broken the skin, just sort of scraped it.

I got nipped by a water snake awhile back though, and a scrape smaller than a paper cut ended up with my whole hand getting covered in blood and my thumb going numb. I was always under the impression that water snakes and garters were very similar, so I guess I'm lucky Houdini is very passive?