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. In the results of the VN test, antiserum immunized with the GN and C78 (JP-I), TM-86w and Miyazaki (JP-II) and 4/91 (793B) vaccine strains could neutralize a high rate of field isolates of homologous genotype (75% of field isolates of JP-I, 100% of that of JP-II and 100% of that of 793B, respectively). For field isolates of JP-III, even though there are no homologous genotype vaccine strain, some strains of JP-III were neutralized with immune serum from vaccine strains of the heterologous genotype. In this study, a correlation between serological property and genotype was found for JP-I, JP-II and 793B. Our results suggested that an effective vaccine could be predicted in accordance with the genotype of 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. These 4/91 isolates were neutralized with serum from birds immunized with 4/91 vaccine. In a challenge-protection test, five groups of chicks were immunized with C78, TM-86w, H120, Kita-1, or 4/91 vaccines and then challenged with JP/Iwate/2005 4 wk after vaccination. A protective effect in the 4/91 and TM-86w vaccine groups was indicated by evaluation of the ciliostasis score of the trachea, the respiratory symptom score, and virus isolation from trachea swab samples after challenge. The results of this study suggested that the 4/91 type of IBV, which is virulent to chicks when compared to vaccine strains, has emerged as a new variant in Japan, and vaccines containing the 4/91 strain or the TM-86w strain could be effective for this variant.