Infectious bursal disease virus structural protein VP 2 expressed by a fowlpox virus recombinant confers protection against disease in chickens

Summary Two fowlpox virus recombinants were constructed which expressed the host-protective antigen, VP 2, of infectious bursal disease virus (IBDV). Recombinant FPV-VP 2.4.3 contained the gene for the VP 2-VP 4-VP 3 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 VP 2 and VP 3 proteins were correctly processed from the polyprotein precursor molecule. Recombinant FPV-VP 2 contained only the VP 2 encoding region under the control of the fowlpox early/late promoter P.E/L inserted immediately downstream of theTK gene. The expression level of VP 2 from FPV-VP 2 was approximately 5 times higher than from FPV-VP 2.4.3. 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-VP 2 developed antibodies to IBDV. When challenged with IBDV (strain 002-73), a significant level of protection was provided by FPV-VP 2 vaccination, although the level was lower than the protection provided by an oil adjuvanted inactivated whole IBDV vaccine. Birds vaccinated with FPV-VP 2.4.3 were not protected from infection as assessed by ELISA for the presence of IBD virus in bursae.