1989 Volume 42 Issue 1 Pages 58-63
Immunosuppressive potentials of attenuated variants (clones Lp and Sp) of infectious bursal disease (IBD) virus to the chickens were investigated comparing with those of virulent RF-1 strain (WT) and tissue culture-adapted RF-1 strain (the parent virus of the clones RF-1tc). After being orally inoculated with these viruses at one day or 21 days of age, the chickens were administered with either Newcastle disease B1 vaccine intranasally, Newcastle disease TCND vaccine intramuscularly or bivalent infectious coryza vaccine intramuscularly; these were administered at 7, 28 or 35 days of age, respectively. Hemagglutination-inhibition antibody titers were assayed at weekly intervals, and resistance to the challenge was tested 4-5 weeks later.
Magnitude of immunosuppression due to the IBD virus varied depending on the virulence of IBD virus, the age of chickens at the time of IBD virus infection, and the sort of vaccine administered. The suppression was largest with WT, moderate with RF-1tc, and no suppression with clones Lp and Sp. Chickens inoculated with IBD virus at one day of age were remarkably suppressed, but those inoculated at 21 days were only slightly. Immunosuppressive effects against Newcastle disease B1 or bivalent infectious coryza vaccines were more severe than that against Newcastle disease TCND vaccine.
The lack of immunosuppression after infection with clones Lp and Sp may reflect our previous results that the histopathological lesions due to the clones are less extensive than those produced by more virulent IBD strains. The results suggest complete attenuation of those clones.