Dual-viral vector approach induced strong and long-lasting protective immunity against very virulent infectious bursal disease virus

To induce strong protective immunity against very virulent infectious bursa l disease virus (wIBDV) in chickens, two viral vector systems, Marek's dise ase and Fowlpox viruses expressing the wIBDV host-protective antigen VP2 (r MDV, rFPV), were used. Most of chickens vaccinated with the rFPV or rMDV al one, or vaccinated simultaneously with both at their hatch (rMDV-rFPV(1d)), were protected against developing clinical signs and mortality; I however, only zero to 14% of the chickens were protected against gross lesions. In contrast, gross lesions were protected in 67% of chickens vaccinated primar ily with the rMDV followed by boosting with the rFPV 2 weeks later (rMDV-rF PV(14d)). Protection against the severe histopathological lesions of rFPV, rMDV, rMDV-rFPV(1d), and rMDV-rFPV(14d) vaccine groups were 33, 42, 53, and 73%, respectively. Geometric mean antibody titers to VP2 of chickens vacci nated with the rFPV, rMDV, rM DV-rFPV(1d), and rMDV-rFPV(14d) before the ch allenge were 110, 202, 254, and 611, respectively. Persistent infection of the rMDV in chickens after the booster vaccination with rFPV was suggested by detection of the rMDV genes from peripheral blood lymphocyte DNA at 28 w eeks of age. These results indicate that the dual-viral vector approach is useful for quickly and safely inducing strong and lone-lasting protective i mmunity against wIBDV in chickens. (C) 2000 Academic Press.