Development of an immune complex vaccine to control variant infectious bursal disease virus (IBDV) infections in the broiler chicken industry in Canada

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Infectious bursal disease virus (IBDV) was first recognized in the USA near the town of Gumboro, Delaware (Gumboro disease). Infectious bursal disease virus belongs to the genus Avibirnavirus of the family Birnaviridae and causes infectious bursal disease (IBD), an acute highly contagious disease of 3- to 6-week-old chickens. The most severe consequence of IBDV infection is the functional loss of the bursa of Fabricius. IBD is one of the most important avian acquired immunosuppressive diseases and has led to large losses to the poultry industry worldwide. IBDVs emerged that could not be controlled by immunization with vaccines prepared from ''classic'' IBDV strains, and were called variants IBDVs (vIBDVs). The control of IBD in Canada has been complicated by the recognition of vIBDVs. Our previous research has identified 43% of broiler flocks or premises (or 52% of barns) in Saskatchewan are infected with vIBDV. It is apparent that flocks with vIBDV infection have a poor feed conversion ratio, high mortality, bursal atrophy and decreased meat production. This has led to an annual loss of over 3.9 million kilograms of broiler production per year in the Saskatchewan broiler chicken industry. This mass of chicken meat lost had a wholesale market value of over $13 million per year. Moreover, in recent years, increased condemnations of broiler carcasses due to bacterial hepatitis was recognized due to immunosuppression. Our research has demonstrated that current vaccination programs against IBDV in the broiler breeder industry in Canada are not effective in controlling vIBDV because of antigenic differences between US-sourced vaccines and vIBDVs circulating in the broiler chicken industry in Canada. Furthermore, we have discovered that current vaccines used in the broiler chicken industry are not able to provide protection against the Canadian vIBDV. Recently, our research revealed an unrecognized phenomenon that the immunization of broilers with vectored vaccine induces immunosuppression that may further increase susceptibility to vIBDV infection. Because of these reasons, we are proposing to develop a IBDV vaccine using Canadian isolates to control vIBDV in the broiler chicken industry in Canada.