permitherin.
Hot shot bed bug/flea spray, gallon costs $12-14. Spray all around the cage(s) and the inside perimeter of the cage every week when you clean for a month or more to kill them off, then spray once a month to keep them away.
And, no, not all rats have them, healthy or not. Get rid of them quick, or they will take over.

For the rats themselves, use Natural Chemistry Reptile Relief spray, but don't feed any to your snakes for at least a week to allow them time to get it off...