Not only do I usually use metronidazole on all new acquisitions, but I typically treat them with albendazole (gets more kinds of tapeworm species than fenbendazole)...and they do need several clean tests because they don't necessarily always show up if they have them. I raise the vast majority of my own feeder rodents and insects, and I treat them a couple times per year also (albendazole don't seem to hurt my lobster roaches any...not really sure what the dose oughtta be, though). If you get feeders from pet shops or jobbers that supply pet shops then feeder rodents could potentially be contaminated by dust, or droppings from birds, imported reptiles, etc. Some people will take a rodent one snake refuses to eat and put it in to feed something else, or back into the breeder colony---also a bad idea. Some parasites don't cause tremendous problems unless the host is unduly stressed, so multi-generational infestations can occur.