Sequence analysis of the S1 glycoprotein of infectious bronchitis viruses: identification of a novel genotypic group in Australia.

Sequencing of the S1 genes of nine Australian strains of infectious bronchitis virus (IBV) identified two genotypically distinct groups of strains. The strains Vic S, V5/90, N1/62, N3/62, N9/74, and N2/75 comprised group I, sharing 80.7-98.3% identity in their deduced amino acid sequences. All group I strains were able to replicate in the trachea and kidney but only four strains, Vic S, N1/62, N9/74, and N2/75, were nephropathogenic, the latter three causing mortalities ranging from 32 to 96%. Group II contained strains N1/88, Q3/88 and V18/91 which only replicated in the trachea, inducing no mortalities. These viruses showed 72.3-92.8% amino acid identity to each other and only 53.8-61.7% identity to viruses of the first group. They were also distinct from the Massachusetts 41 and D1466 strains (47.5-55.7% amino acid identity). Thus N1/88, Q3/88 and V18/91 form a new group of viruses which are genotypically distinct from all previously characterized IBV strains. No definite correlations were established between the S1 amino acid sequences and the nephropathogenicity of strains.