Genetic variability of respiratory syncytial virus isolated during the last 20 years from Sapporo

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The genetic variability of 125 respiratory synsytial virus (RSV) subgroup A and 32 subgroup B isolates over 19 epidemics from 1980 to 1999 in Sapporo city was investigated. Allocation of isolates into lineages was archived by RT-PCR of selected regions of large glycoproteins (G) gene followed by RFLP analysis and/or direct sequencing of RT-PCR product. In RSV subgroup A isolates 10 different genetic lineages were identified. The strains with the same genotypes were isolated in each epidemic and the dominant lineages were replaced by others after every one to three consecutive epidemics. However there was no apparent accumulation of diversity with age to indicate progressive changes. The dominant strains were often closely related to those isolated in other parts of the world at a similar time.Phylogenic analysis of nucleotide sequences of G gene of 32 RSV subgroup B strain revealed seven distinct branches in which strains isoalted during seasons of close proximity were located. There was a tendency for recent isolates to lie at the end of each branch and these linear evolutionary changes were typically represented in a branch containing nine strains isolated during 6 seasons from 1980 to 1986.