Detection of vaccine-like infectious bursal disease (IBD) virus in IBD vaccine-free chickens in Japan.

The prevalence of infectious bursal disease virus (IBDV) was studied in chickens, which had not been vaccinated against IBD. Fifty sera and forty-six bursae of Fabricius from chickens showing impaired growth, collected from 7 IBD vaccination-free farms in Japan were used for virus neutralization (VN) tests and RT-PCR for detection of IBDV genome corresponding to the VP2 hypervariable region. Of the fifty sera, 39 sera (78%) from 6 farms were VN antibodies positive. Of the forty-six bursae, 37 bursae (80.4%) from 6 farms were positive in the RT-PCR assay. The sequences of all the RT-PCR products detected in this study were closely related or identical to those of the vaccine strains. These results show that vaccine-like IBDV is prevalent even in IBD vaccine-free chicken farms in Japan.