Cryptosporidial infection in chickens.

Cryptosporidial infection was found in 25 layer and four broiler chickens, aged 40 to 80 days, from 11 flocks on six poultry farms. The infection appeared in 1975 in broiler chickens and in 1976 in layers. On one of the poultry farms the infection occurred over a period of 2.5 years. Tissues most frequently affected with cryptosporidia were the bursa of Fabricius (85%), followed by the respiratory tract (nasal cavity, infraorbital sinus, larynx and trachea) (41%) and caeca (11%). Cryptosporidia in various stages of its life cycle were demonstrated histologically and electron microscopically attached to the host cells, and they were identical to those previously reported in other animals and humans. Hypertrophy and hyperplasia of the lining epithelial cells were noted in both the bursa of Fabricius and the respiratory tract. The histological alterations in the respiratory tract, especially the trachea, were sufficient to consider cryptosporidia as a primary cause of respiratory disease.