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.