Urinary tract cryptosporidiosis in commercial laying hens

Formalin-fixed kidney tissues from adult egg-laying chickens in two houses of an egg-production complex in the upper Midwest were submitted to Iowa St are University for histopathologic examination. An increased incidence of v isceral gout, average daily mortality 1%-2% higher than expected, and egg p roduction within normal limits were observed in both houses. Numerous devel oping stages of Cyptosporidium were observed on the apical surface of epith elial cells lining renal collecting tubules and ureters. Scanning and trans mission electron microscopy were used to visualize colonization of cryptosp oridia, disruption of microvilli, and exfoliation of parasitized epithelial cells. Lymphoplasmacytic infiltration in the wall of ureters and hyperplas ia of parasitized epithelial cells resulted in partial obstruction of urete rs, which may have induced visceral gout in affected hens. This is the firs t report of urinary tract cryptosporidiosis occurring in adult hens in a mo dern commercial egg-production facility.