Infectivity and distribution of infectious bursal disease virus in the chicken. Persistence of the virus and lesions.

Chickens susceptible to infectious bursal disease (IBD) became viremic for only a transient period when inoculated with two different strains of infectious bursal disease virus (IBDV). The virus was not isolated from tissues beyond 10 days postinoculation. There was no apparent spread of IBDV to susceptible contact chickens placed with infected groups 16, 30, 42, and 52 days postinoculation. At three days postinoculation, the virus was consistently isolated in the highest concentration from the bursa of Fabricius and spleen whereas the brain and blood were low in yield. In contrast, 1-day-old chicks from IBD-immune parent stock were resistant to infection when inoculated with embryo-adapted IBD vaccine virus. This observation may explain failures to obtain an active immune response when chickens possessing high levels of parentally conferred immunity are vaccinated at an early age. Bursae of chickens were markedly atrophied upon gross examination 33, 51, and 71 days after infection. The lymphoid follicles were severely depleted at 33 and 51 days; at 71 days, repopulation of lymphocytes was commencing. Uninoculated control chickens possessed normal-appearing bursae throughout the experiments. The diagnostic implications of the findings are given.