Poorly fed birds are more susceptible. Coccidiosis in chickens is generally classified as either intestinal or cecal. Most serious cases of intestinal coccidiosis in Alberta are caused by E. necatrix. Cecal coccidiosis is due to E. tenella. Coccidiosis occurs most frequently in young birds.
Old birds are generally immune as a result of prior infection.
Severe damage to the ceca and small intestine accompany the development of the coccidia. Broilers and layers are more commonly infected, but broiler breeders and turkey and pheasant poults are also affected. E. acervulina and E. maxima develop in epithelial cells within the small intestine and generally cause chronic intestinal coccidiosis. The most easily recognized clinical sign of severe cecal coccidiosis is the presence of bloody droppings. Dehydration may accompany cecal coccidiosis.