RECOMBINANT FOWLPOX VIRUS-VACCINES AGAINST AUSTRALIAN VIRULENT MAREKS-DISEASE VIRUS - GENE SEQUENCE-ANALYSIS AND COMPARISON OF VACCINE EFFICACY IN SPECIFIC PATHOGEN-FREE AND PRODUCTION CHICKENS

We have cloned and sequenced the glycoprotein genes gB, gC and gD of t he Australian virulent Marek's disease virus (MDV) isolate Woodlands N o.1. The glycoprotein gB and gC sequences were identical to the homolo gs of other virulent MDV type 1 strains, and the glycoprotein gD seque nce contained only one unique amino acid substitution. Recombinant fow lpox viruses (rFPVs) expressing the MDV glycoprotein genes were constr ucted and their efficacy as vaccines was evaluated in specific pathoge n free (SPF) and production chickens. Vaccination with the FPV-gB reco mbinant protected SPF chickens from Marek's disease mortality and tumo ur formation following challenge with virulent MDV Woodlands No.1. The degree of protection from Marek's disease was dependent on the vaccin e dose and route of inoculation. The rFPVs expressing gC or go did not provide protection from Marek's disease. A rFPV expressing both gB an d gC did not provide enhanced protection in comparison with the rFPV-g B alone. The rFPV-gB vaccine failed to protect commercial chickens fro m MD mortality and provided little protection from tumour formation in comparison with the commercial herpesvirus of turkey (HVT) vaccine. T he failure to provide protection against MD may be related to the impa ct of maternally derived immunity to MDV and FPV and possibly the geno type of the chickens. (C) 1997 Elsevier Science B.V.