Respiratory cryptosporidiosis in chickens.

In order to better characterize spontaneous respiratory cryptosporidiosis in chickens, a retrospective examination of histopathology reports from the Georgia Poultry Laboratories for an 18-mo period (4/1/86 to 9/30/87) was made; 12 cases were found. Collected data were analyzed and certain epidemiologic and histologic features were identified. Eleven of the 12 cases involved broiler type chickens. The ages of chickens with respiratory cryptosporidiosis were evenly distributed between 17 and 52 days of age. The infected birds were always clinically ill. Viruses or bacteria or both often accompanied respiratory Cryptosporidium sp. infections. Histologic lesions (including those of ciliary-adherent bacteria) are described. As the inflammatory response in infected organs became progressively nonpurulent (lymphocytes and plasma cells predominate), numbers of Cryptosporidium diminished. Cytologic preparations were useful for making diagnoses of respiratory cryptosporidiosis in chickens. Identification of epidemiologic features of respiratory cryptosporidiosis, and improved ability to make accurate and prompt diagnoses of Cryptosporidium sp. infection, are vital for a more complete understanding of the impact of this disease on poultry health.