[h2odragon]

I'll give you one (total supposition, I Am Not A Veterinarian): most people don't "get infected" with worms, but some have exposure and have immune responses that may not ever rise to the level of "symptoms". anti-parasitcs might assist and allow more robust responses to other health challenges.

Don't look too deep into how much life we host even when healthy; it'll squick you out.