Infection is distributed through contaminated feed and water.
The disease is commonly diagnosed in birds between 3 and 6 weeks old. Gross lesions can be seen for the most part on the bursa of Fabricius. The bursa may be swollen, or show signs of hemorrhage. In some cases, however, no lesions are observed and the bursa shrinks in size. Chickens with the disease exhibit anorexia, depression, watery diarrhea, ruffled feathers, soiled vent feathers, vent picking, and death.