It will not hurt them.
Without seeing what you saw, it's hard to say if you saw an actual parasite in a dropping, or if it might have been a maggot, which would have been laid in the dropping by some kind of flying insect after the dropping was deposited there. If the dropping wasn't fresh, then maggots are possible. The parasites most commonly seen in droppings are roundworm (large or small) or tapeworm. A maggot will have an identifiable 'head' end on it, parasites that chickens carry do not have a 'head' end. Roundworm resembles cooked spagetti (large) or threads (small), and tapeworm segments resemble rice grains, that move when fresh.