This discussion has been thought provoking and productive, Marian. Thanks for keeping it going
. It might be surprising to learn that even live worms (like nightcrawlers) carry roundworms, but sometimes they're almost essential to use to get newborn snakes to feed or to get problem feeders motivated. Freezing fish for at least three days kills most pathogens, but not all. There are a lot of ways that captive snakes can acquire parasites, even with very strict husbandry techniques. Yet, most snakes survive quite well with low level infestations. They don't become a problem until the snake gets stressed or sick from other reasons.
Rick