Start with clean rodents an good bedding. If you get fleas you can use a ton of products but the safest for your snakes is Diatomaeus Earth. A little DE goes a long way. Or just gas an freeze everything. The flea/lice eggs won't survive a deep freeze.
The really bad thing about fleas is they are the vector for tapeworms. The flea carries the tapeworm larvae. So if your rat has fleas an carries worms an then you feed live, you just gave the snake worms.
To treat rats an rabbits for worms go to TSC an get some liquid chicken wormer. Google or yahoo or youtube how to use it. But it's more or less six drops for a rabbit an three for adult rats every three days for a week. Then you can't eat or feed the rat/rabbit off after 30days. I wouldn't feed any rodent treated for worms off, not going to risk my snakes. Yes, if a snake has worms, one treatment is loading the prey, But that's a known amount of medicine. An animal that's been treated would have a unknown residual amount. That amount could be bad for my snakes. So, I would breed the treated for a new colony an sell off adults as pet trade or fish bait.
Yes, more info then you wanted. Google how to prevent fleas in the barn or farm animals. You'll learn a ton which is much better then learning it first hand.
Always wash your hands before an after handling rodents, even your pet rabbit. Ask my kids how they know:( Leptospirosis
Good luck!
