An outbreak of infectious bursal disease among chickens between 16 and 20 weeks old.

Infectious bursal disease (IBD) was diagnosed in a flock of 1,031 broilers and cockerels aged between 16 and 20 weeks. Affected birds passed whitish, watery feces. On postmortem examination, the bursa of Fabricius (bursa) was enlarged and the kidney tubules were well distended. Histopathological sections of the bursa were characterized by edema, destruction of lymphocytes, and heterophilic infiltration. Spread was rapid, and the average mortality rate was 3.5%. Bursal homogenates from dead chicks produced precipitation lines with known IBD antiserum in the agar-gel diffusion precipitation test. Sera collected from surviving chicks 10 days after the onset of the outbreak also gave precipitation lines with known IBD virus antigen. Fresh bursal homogenates from dead chicks administered intraconjunctivally to susceptible chicks exhibited typical IBD.