Molecular evolution of attachment glycoprotein (G) gene in human respiratory syncytial virus detected in Japan 2008-2011.

We investigated the evolution of the C-terminal 3rd hypervariable region of G gene in the prevalent human respiratory syncytial virus (RSV) subgroups A (RSV-A) and B (RSV-B) in Japan in 2008-2011. Phylogenetic analysis and the evolutionary timescale was obtained by the Bayesian Markov Chain Monte Carlo method. All 38 RSV-A strains detected were classified into genotype NA1 and the 17 RSV-B strains detected belonged to genotypes BA and GB2. NA1 subdivided around 1998 in the present phylogenetic tree. Genotype BA subdivided around 1994. The evolutionary rates for RSV-A and RSV-B were estimated at 3.63×10⁻³ and 4.56×10⁻³ substitutions/site/year, respectively. The mean evolutionary rate of RSV-B was significantly faster than that of RSV-A during all seasons. The pairwise distance was relatively short (less than 0.06). In addition, some unique sites under positive selection were found. The results suggested that this region of the RSV strains rapidly evolved with some unique amino acid substitutions due to positive pressure.