Infectious bursal disease virus structural protein VP2 expressed by a fowlpox virus recombinant confers protection against disease in chickens.

Two fowlpox virus recombinants were constructed which expressed the host-protective antigen, VP2, of infectious bursal disease virus (IBDV). Recombinant FPV-VP 2.4.3 contained the gene for the VP 2-VP4-VP3 polyprotein under the control of the vaccinia virus late promoter P.L 11 inserted within the thymidine kinase (TK) gene of FPV. In infected chicken embryo skin (CES) cells VP2 and VP3 proteins were correctly processed from the polyprotein precursor molecule. Recombinant FPV-VP2 contained only the VP2 encoding region under the control of the fowlpox early/late promoter P.E/L inserted immediately downstream of the TK gene. The expression level of VP2 from FPV-VP2 was approximately 5 times higher than from FPV-VP2.4.3. Wing web inoculation of birds resulted in the development of typical fowlpox lesions and the development of antibodies to FPV with either of the recombinants, but only birds vaccinated with FPV-VP2 developed antibodies to IBDV. When challenged with IBDV (strain 002-73), a significant level of protection was provided by FPV-VP2 vaccination, although the level was lower than the protection provided by an oil adjuvanted inactivated whole IBDV vaccine. Birds vaccinated with FPV-VP2.4.3 were not protected from infection as assessed by ELISA for the presence of IBD virus in bursae.