Immunogenicity and antigenicity of very virulent strains of infectious bursal disease viruses in chickens

The immunogenicity and antigenicity of three very virulent strains of infectious bursal disease viruses (vvIBDVs) from Turkey, Holland and Taiwan were investigated and their antigenic relationships with the American classic (SAL), variant (IN) serotype 1, and serotype 2 OH IBDVs were studies. The vvIBDVs were passaged 8 times in chicken embryos and were characterized by RT/PCR-RFLP using restriction enzyme MboI and Bs tNI. The RFLP profile patterns of these viruses did not change after 8 passages in chicken embryos.; Since it was not possible to adapt the vvIBDVs to cell culture, the antigenic relatedness between these viruses and the American strains were established by using cross-neutralization test in chicken embryos. The results revealed that the vvIBDVs are antigenically related to the classic SAL but are antigenically different from the variant IN serotype 1 strain and serotype 2 OH strain of IBDV.; For the immunogenicity study, inactivated vaccines prepared from the vvIBDVs and containing 10 5ELD50 of each virus provided full protection against the classic STC but provided no protection against the variant IN strain at 5 and 10 days postchallenge.; The pathogenicity and persistence of the cell-culture derived and the bursa-derived variant IN strain of IBDV were also investigated in Specific-Pathogen-Free (SPF) and commercial chicks. The original virus was bursa derived then passaged 10 times (LP) or 47 times (HP) in BGM-70 cells. Two concentrations of the LP virus were used for different groups of birds, high titer 1.5 x 10 5 EID50 and low titer 1.5 x 102EID 50.; The results revealed that only the bursa-derived virus is pathogenic and the virus was isolated in chicken embryos up to 10 days post inoculation (PI). The virus antigen was detected by immune-electron microscopy (IEM), antigen-capture-immunosorbent assay (AC-ELISA) up to 7 days PI and by immunoflourescence assay (IF) up to 10 days PI. The virus was detected in the Bursa of Fabricius (BF) up to 21 days PI whereas the viral RNA was detected up to 28 days PI in the chickens inoculated at 3 weeks old.; When the bursa-derived virus was inoculated in SPF and commercial one day old chicks, the virus was detected up to 14 days PI in both SPF and commercial chicks.; The cell culture-derived viruses lost their pathogenicity after passage in BGM-70 cells and the virus was isolated in chicken embryos only at 3 days PI in LP at high concentration and HP virus inoculated birds. The virus antigen was not detected in the BF by IEM, IF or AC-ELISA at any intervals PI and only detected at 3 days PI by RT/PCR in the BF of birds inoculated with LP virus at high concentration.; When the IBDV vaccine strain was inoculated into one-day-old SPF and commercial chicks, the virus was detected up to 14 days PI by RT/PCR in BF of SPF chicks but was not detected in BF of commercial chicks.