Genetic variation in the conservative gene region of norovirus genogroup II strains in environmental and stool samples

Noroviruses (NoVs) have been one of leading etiological agents for infectious gastroenteritis over the world. Gastroenteritis caused by NoVs is prevalent in winter season, and the contamination of the water environment with NoVs in the epidemic cold season is frequently reported. In contrast, the number of gastroenteritis patients and NoVs in the water environment are reduced during the non-epidemic summer season, and the year-round fate of NoVs has remained to be elucidated. In this study, we collected nucleotide sequences of NoV genogroup II (GII) from domestic sewage, sewage sludge, treated wastewater, river water, and stool samples of gastroenteritis patients in geographically close areas. Phylogenetic analysis of the obtained NoV gene revealed that six out of seven isolates from environmental samples and 10 out of 11 isolates from stool samples belong to genotype 3 (NoV GII. 3) or 4 (NoV GII. 4), which have been prevalent throughout the world. Genetic distances between the conservative gene region of NoV GII. 4 variants implied that genetically diverse strains are likely to occur in environmental samples. The evaluation of the evolutionary change of NoV gene obtained from environmental samples would make it possible to elucidate the year-round fate of NoVs.