Spread and predominance in Japan of novel G1P[8] double-reassortant rotavirus strains possessing a DS-1-like genotype constellation typical of G2P[4] strains

Rotavirus is a major cause of severe gastroenteritis in children <5 years of age worldwide, and two, live attenuated rotavirus vaccines are globally available. As rotavirus vaccines are introduced into national immunization programs, there is an increasing need to monitor circulating wild-type strains. However, few studies have systematically examined their full genotype constellation. This study was therefore undertaken to characterize the whole genotype constellation of circulating rotavirus strains in three widely-separated locations in Japan during the 2012 rotavirus season when rotavirus vaccines became available in the country for the first time. Of 107 rotavirus-positive specimens, 50 (46.7%) strains collected from all three locations possessed an unusual G1-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 constellation in which a typical G2P[4] strain appeared to have acquired its two surface protein genes from the most common G1P[8] strain. These G1P[8] double-reassortant strains were shown to possess the 11 genome segments virtually indistinguishable from each other in their nucleotide sequences and phylogenetic lineages except for two strains that underwent further intra-genotype reassortment. Successful spread to and predominance in broad locations across Japan of novel rotavirus strains possessing a genotype constellation that was previously thought not to be preferred suggests unexpected genomic flexibility of the genotype constellation.