Intestinal Protozoa Important to Poultry

Parasites of two groups are important in poultry, the coccidia and the mastiogophora (flagellates) (Table 1). Most of the Coccidia in poultry are in the genus Eimeria, but a few species of Isospora, Cryptosporidium, and Sarcosporidia are represented. The Eimeria are best known, with seven important species recognized in chickens and several others in turkeys. Diagnosis of coccidiosis is by recognition of classic signs and lesions, by gross examination, and can be aided by microscopic examination of feces and intestinal contents. Control of coccidiosis is by preventive use of anticoccidials and by immunization. Cryptosporidium are common in poultry but little is known of their importance, except for the occasional outbreak of respiratory cryptosporidiosis in turkey poults. Of the flagellates, Histomonas meleagridis is the best known. Infections in turkeys may cause near 100% mortality, but outbreaks in chickens are more often marked by morbidity and subsequent recovery. Recent outbreaks in broiler breeder pullets caused excessive losses from mortality (5 to 20%) culling, and overall poor flock performance. Histomonas organisms are carried by eggs of the cecal worm Heterakis gallinarum enabling them to survive for long periods in soil as a source of infection. In the U.S. there are no products available for treatment of blackhead. Preventive use of anthelminthics to destroy the cecal worm carrier show some promise in reducing exposure.