Some coccidia is good for chicks. They cannot develop the immunities they need to fight it unless they are exposed to it in low numbers. The problem is when the numbers get out of hand. That can be fatal. The trick is seeing that they are exposed to some but not too many. That “bug” can thrive in wet conditions. A wet brooder, wet coop, wet run, or any wet ground with chicken poop in it is a potentially dangerous area. Normally if they are exposed to low levels of it they will develop immunity in two to here weeks, but you need to know the signs and be ready to treat if necessary. Some people have a history if it but we all need to be vigilant, history or not. I feed dirt from the run to my chicks in the brooder starting from day 2 so they can develop that immunity before they hit the ground. My chicks with broodies are also exposed to run dirt at a very young age.
The potential for parasites comes with any animal, not just chickens. Your pet dog or cat has that potential, even if kept in the house most of the time. Earthworms can potentially carry gapeworms or roundworms. Grasshoppers, slugs, and some other things they love to eat can potentially infest them with some type of parasite. Wild birds visiting in their coop or run can potentially spread parasites. This does not mean that every chicken that eats just one earthworm will automatically be infected with gapeworm and roundworms, but the potential is there. The vast majority or earthworms are not infected, at least not around here, because my chickens eat a bunch after a rain and they have never has an infestation. Again it is something we need to be vigilant about whether they are in the brooder, coo, coop and run, or free ranging. The potential is there but from my experiences my potential is really low for earthworms causing a problem. If my experiences were different I’d feel differently.
