Serological studies of infectious bronchitis vaccines against Japanese field isolates of homologous and heterologous genotypes.

The genetic diversity of the partial S1 gene involving the hyper variable region for infectious bronchitis (IB) vaccine strains in Japan were compared with those of IB virus isolated from the field in Japan. Field isolates have mainly been classified into three major genotypes, JP-I, JP-II and JP-III, since 2003; however, the 4/91 genotype was detected from recent field isolates in Japan. The virus neutralization (VN) activity with vaccine immunized serum was investigated to evaluate the protective effects of vaccines against Japanese field isolates.

Isolation of 4/91 type of infectious bronchitis virus as a new variant in Japan and efficacy of vaccination against 4/91 type field isolate.

Among field isolates of infectious bronchitis virus (IBV) from recent outbreaks, some isolates that were classified into the 4/91 genotype, by analysis of the S1 gene, have been confirmed to be a new variant in Japan. To elucidate the characteristics of these isolates, pathogenicity in chicks and the efficacy of vaccines against this new variant were examined. Severe respiratory symptoms were observed in 4-day-old specific pathogen free chicks inoculated with a 4/91 genotype isolate, either JP/Wakayama/2003 or JP/ Iwate/2005; body weights 3 wk after inoculation were significantly lower than those of chicks inoculated with a 4/91 vaccine strain.