Gomis, Susantha2020-05-122021-05-122020-042020-05-12April 2020http://hdl.handle.net/10388/12832We have previously demonstrated that vaccines used in Canada against infectious bursal disease virus (IBDV) are not effective in controlling variant IBDVs (vIBDVs) in the broiler chicken industry. The objective of this study was to develop an immune complex (Icx) vaccine using vIBDV SK09 to immunize broiler breeder parents to protect their progeny broilers against vIBDVs. The immunoprotective ability of broiler chicks carrying maternal antibodies (MaAb) or control groups with no MaAb against IBDV was studied by challenging with vIBDV SK09, SK10 or SK11 at day-6 of age. The immunoprotective efficacy of SK09 vaccine formulations were compared with commercial IBDV vaccines used in broiler breeders. Bursa of Fabricius (BF) samples were collected at 3, 6, 9, 13, and 29 days post-challenge for viral load detection using RT- qPCR. Viral load peaked at 3-days post- challenge (dpc) in broiler chicks obtained from unvaccinated breeders as well as in broiler chicks obtained from broiler breeders immunized with commercial IBDV vaccines. However, viral loads decreased later in these groups but were significantly higher compared to our IBDV vaccine formulation groups. Viral load in the BF of broilers was not detected up to 13 dpc in all progeny groups from parents vaccinated with SK09 Icx. However, we detected significantly higher viral loads in the BF samples obtained from these groups at 29 dpc. This data suggests that passive immunity induced by breeder vaccination programs were able to protect broilers against vIBDV challenge at least up to 13 dpc. Nevertheless, they failed to provide sterile immunity as viral load significantly increased at 29 dpc. This data further suggests that delayed viral replication or probably challenged vIBDV hiding somewhere in broiler chicks that showed up when MaAb waned. It shows that B-lymphocytes significantly depleted in unvaccinated control and commercial vaccine groups by 3 dpc by flow cytometry. In contrast, B-lymphocyte numbers were normal in other groups up to 13 dpc; however, by 29 dpc B-lymphocytes were significantly depleted in all breeder vaccine programs. Altogether, our data suggest that the broiler breeder vaccination program against vIBDV SK09 can protect broiler chicks for the first three weeks of age but may not be able to provide complete protection even against vIBDV as SK09. Hence, this study demonstrates the importance of introducing a broiler vaccine to control vIBDVs circulating in the Canadian broiler chicken industry.application/pdfIBDVimmune complexvaccineThesis2020-05-12