Effect of recombinations on changes in genotype proportions between norovirus seasons in Japan

Abstract

Background: Norovirus (NoV) is an etiological agent of acute gastroenteritis in humans. Genomic recombinations in NoV occur mainly at the junction of the genes encoding the RNA-dependent RNA polymerase (RdRp) and the major capsid protein (viral protein 1, VP1), which may produce strains with novel combinations of VP1- and RdRp-genotypes. Methods: Here the effect of recombinations on changes in the proportions of VP1-genotypes was examined through analysis of the observed frequencies of VP1-genotypes in Japan from season 2006/2007 to 2019/2020 reported in the Infectious Agents Surveillance Report (IASR) and the nucleotide sequences for 2788 GI and 19,782 GII strains deposited in the International Nucleotide Sequence Database (INSD). Results: Positive correlation was identified between the observed frequency in the IASR and the number of nucleotide sequences in the INSD for individual VP1-genotypes in each season. In addition, acquisition of novel RdRp-genotypes was associated with an increase in the observed proportion of VP1-genotypes. Conclusions: Recombinations creating strains with novel combinations of VP1- and RdRp-genotypes may be an adaptive mechanism for NoV.