A new genotype of nephropathogenic infectious bronchitis virus circulating in vaccinated and non-vaccinated flocks in China.

Five strains of infectious bronchitis virus (IBV) were isolated from five layer flocks that had nephropathogenic infection in four provinces in China. Among them, three of the five flocks had been vaccinated against infectious bronchitis. Virulence studies indicated that the five Chinese IBV isolates caused 10 to 30% mortality in 15-day-old specific pathogen free chickens and gross lesions were mainly confined to the kidneys in all of the dead chickens. Two oligonucleotide pairs, S1Uni2 and S1Oligo3' or S1Oligo5' and S1Oligo3', were used after propagation of the isolates in embryonated eggs to amplify the S1 protein genes of the spike protein. The cDNA derived by reverse transcriptase-polymerase chain reaction was cloned and sequenced. The nucleotide and amino acid sequence of S1 protein gene had a similar degree of identity (> or =92%) among the five Chinese IBV isolates. The nucleotide and amino acid identity of the S1 protein gene between the five Chinese IBV isolates and 16 strains of other IBVs varied from 60 to 81%. This clearly showed that the five Chinese IBV isolates comprised a separate genotype. These results demonstrated, for the first time, that there is a new genotype of nephropathogenic IBV circulating in vaccinated and non-vaccinated flocks in China.