The term parasite refers to a life-form that harms another life-form in order to survive. Technically, since the worms thrived inside Fry and improved his biologic functions to the point where he was much more intelligent and much stronger, they would not be parasites, but, rather, symbiotic with Fry.
When Fry took out the holophonor, Leela said that only a few people in the world can play that. At the last scene, Fry took out what seems to be a beginner's guide to playing holophonor, suggesting it is plentiful or common enough for tutorial books to exist.