It causes marked morbidity and mortality in affected flocks. Although the disease causes severe losses, its affect on reducing the bird's ability to develop immunity to other diseases may be the most serious effect produced by this disease. It is extremely contagious. Birds have ruffled feathers, a slight tremor at onset of the disease, strained defecation, loss of appetite and are dehydrated. Affected birds have a tendency to sit and when forced to move, have an unsteady gait.
Vent picking is common and a whitish diarrhea frequently develops.
A sudden rise in body temperature is followed by a drop to subnormal temperature, prostration and death. Birds surviving the initial infection will recover rapidly within two weeks. Postmortem lesions include dehydration and changes in the bursa, skeletal muscle, liver and kidneys. Within a few days the bursa shrinks to half its normal size or smaller. Diagnosis of infectious bursal disease is based on flock history and postmortem lesions.