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.


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