The genus Sapovirus currently contains only one recognized species, the Sapporo virus, which was discovered in 1977 in Sapporo, Japan [8] . The SaV genome is approximately 7.1 to 7.5 kb in length, and may have two or three ORFs. ORF1 encodes a polyprotein that undergoes proteolytic cleavage to form the non-structural proteins and the major capsid protein VP1. ORF2 encodes the minor structural protein VP2. ORF3 encodes a small basic protein of unknown function [9, 10] . Interestingly, it is located in an overlapping reading frame within ORF1, and is present only in SaVs from selected genogroups. At present, SaVs are classified formally into 5 genogroups based on phylogenetic analysis of the full-length VP1 sequence, though additional genogroups have been proposed to accommodate some novel SaVs discovered in recent years. Further classification of SaVs into genotypes has also been undertaken, though taxonomic assignment at the genotype level appears to be less well-defined than at the genogroup level [11] .