INTRA-SEASON AND INTER-SEASON GENETIC-VARIABILITY IN THE VP7 GENE OF SEROTYPE-1 (MONOTYPE-1A) ROTAVIRUS CLINICAL ISOLATES

Nucleotide sequence variation was detected in the VP 7 gene of serotype 1 (monotype 1 a) rotavirus isolates collected from children admitted to hospital in Melbourne with acute diarrhoea in 1990 and 199 1. Two co-circulating electropherotypes were detected during the 1991 winter epidemic. Using chemical cleavage of mismatches in heteroduplexes, the genes encoding VP 7 were found to be genetically stable within each electropherotype during the study period, although differences between the two types were apparent. Direct nucleotide sequencing confirmed this finding. The two electropherotypes exhibited four nucleotide differences in the VP 7 gene, only one of which resulted in a substitution in the deduced amino acid sequence. The degree of variation was more pronounced between the 1991 isolates and those from the previous winter, with approximately 3% nucleotide sequence diversity between isolates from both winters. The regions encoding the neutralization epitopes of VP7 were conserved among all isolates. Comparison to the local prototype monotype 1 a strain, RV 4 (isolated from a child admitted to hospital in Melbourne in 1981), implies that the 1990 and 1991 isolates have diverged independently. This suggests that genetically distinct strains emerge from a pool of related viruses to predominate in any given year.