Immunosuppression and histopathological changes in the bursa of Fabricius associated with infectious bursal disease vaccination in chicken.

The effect of the infectious bursal disease (IBD) live virus vaccine on the immune response of chicken was evaluated by the assessment of antibody response following vaccination as well as resistance to challenge with virulent virus. Birds were vaccinated at various ages and later challenged with a heterologous vaccine (NDV) or wild-type IBD virus. The BF was examined for histological changes at regular intervals. Antibody levels to NDV were monitored. Significantly higher mortality rates were observed in birds vaccinated with IBD vaccine than unvaccinated birds (P less than 0.01) following challenge, BF from vaccinated birds showed marked lymphocyte depletion and cellular infiltration with mononuclear cells. Intraocular NDV (NDV-i/o) vaccine given at day old largely prevented the immunodepressive effect of IBD vaccination on NDV vaccine. Groups that received IBD vaccine on day 14 but no NDV i/o suffered higher mortality (41.2%) and showed lower antibody response than those vaccinated on day 1 (0%) or controls which did not receive IBDV (11.8%).