It would be best if you can get your snake converted over to night crawlers and/or pinky mice and frozen thawed fish.
Many frogs and toads carry a heavy parasite load. Switching your snake over to the other food source will for the most part eliminate the chance of parasite introduction.
Here's a link to the care sheet. It gives a lot of great information on feeding and other topics.
Garter Snake Care Sheet - Caresheets