Caecal Worms are very common. They don't actually do much damage, however blackhead organisms can live in the worms eggs for many months and cause Blackhead many months later which can kill Turkeys.
Blackhead really is something to consider carefully if you keep Chickens and Turkeys. It is usually best not to keep them on the same ground together because of cecal worms causing Blackhead. Cecal worms infestations occur directly by birds eating eggs that have been passed out in droppings following what is known as a direct life cycle.
None. Birds will carry cecal worms without showing any ill-effects.