The pathogenicity of Cryptosporidium parvum Tyzzer, 1912 and C. Baileyi Current, Upton et Haynes, 1986 for chickens.

Clinical symptoms and pathological-morphological changes in the respiratory tract of chickens inoculated with Cryptosporidium parvum were described for the first time and compared with those induced by Cryptosporidium baileyi. Intratracheal inoculation with these two species caused symptoms of a respiratory tract disease in all chicken, but a disease of the digestive tract or death did not occur in any case. Pathological and morphological changes were observed only in the respiratory system and were characterized by petechiae in the mucous of larynx, trachea, primary bronchi and in the wall of air sacs in chickens infected with C. parvum, or by diffuse hyperaemia of respiratory tract mucosa in chickens infected with C. baileyi. The pathological-histological changes, which were characterized by affections of various degrees in epithelial cells, mucous glands, and lamina propria mucosae, were more pronounced in the chickens infected with C. parvum.