Characterization of genome sequences and clinical features of coxsackievirus A6 strains collected in Hyogo, Japan in 1999-2013.

Coxsackievirus A6 (CV-A6) is an enterovirus, which is known to cause herpangina. However, since 2009 it has frequently been isolated from children with hand, foot, and mouth disease (HFMD). In Japan, CV-A6 has been linked to HFMD outbreaks in 2011 and 2013. In this study, the full-length genome sequencing of CV-A6 strains were analyzed to identify the association with clinical manifestations. Five thousand six hundred and twelve children with suspected enterovirus infection (0-17 years old) between 1999 and 2013 in Hyogo Prefecture, Japan, were enrolled. Enterovirus infection was confirmed with reverse transcriptase-PCR in 753 children (791 samples), 127 of whom (133 samples) were positive for CV-A6 based on the direct sequencing of the VP4 region. The complete genomes of CV-A6 from 22 positive patients with different clinical manifestations were investigated. A phylogenetic analysis divided these 22 strains into two clusters based on the VP1 region; cluster I contained strains collected in 1999-2009 and mostly related to herpangina, and cluster II contained strains collected in 2011-2013 and related to HFMD outbreak. Based on the full-length polyprotein analysis, the amino acid differences between the strains in cluster I and II were 97.7 ± 0.28%. Amino acid differences were detected in 17 positions within the polyprotein. Strains collected in 1999-2009 and those in 2011-2013 were separately clustered by phylogenetic analysis based on 5'UTR and 3Dpol region, as well as VP1 region. In conclusion, HFMD outbreaks by CV-A6 were recently frequent in Japan and the accumulation of genomic change might be associated with the clinical course.