Cryptosporidia in the bursa of Fabricius--a correlation with mortality rates in broiler chickens

Lung, trachea and bursa of Fabricius were collected from broilers between 14 and 49 days of age from eight flocks with varying levels of mortality and air sac disease (air sacculitis often accompanied by pericarditis and perihepatitis). These tissues were screened for the presence of Cryptosporidia sp. Bursal cryptosporidial infection was present in two flocks between 21 and 42 days of age. These two flocks had a high incidence of air sac disease and the highest overall mortality of the eight flocks between 15 and 49 days of age. Weekly mortality rates increased and remained elevated with the onset and persistence of cryptospordial infection. Mortality was lower when no crypto-spordia were found. The incidence of air sac disease did not decrease when cryptosporidia were no longer present.