Family: Caliciviridae

Genus: Sapovirus

Distinguishing features

The strains in this genus form a distinct clade within the family Caliciviridae (Figure 4. Caliciviridae).   

Virion

See discussion under family description. 

Genome organization and replication

Although Sapporo virus is the exemplar isolate for the type species, Sapporo virus, of this genus, the first reported full-length genomic sequence (7.4 kb) was Manchester virus which was detected in a fecal specimen from a young child (Liu et al., 1995) Subsequently sequences for a range of sapoviruses including the “porcine enteric calicivirus” (PEC strain Cowden) became available. The Manchester virus genome is organized into three ORFs, two with known function. ORF1 encodes the non-structural polyprotein together with the major structural capsid protein gene (VP1) in frame with the non-structural polyprotein coding sequence. In PEC, ORF2 overlaps ORF1 in a −1 frameshift and encodes a predicted small protein likely the equivalent of VP2 in noroviruses. ORF3 begins 11 nt downstream from the predicted start codon of the VP1 in a +1 frameshift and encodes a predicted protein of approximately 160 aa. In some strains of viruses in this genus, and in the PEC Cowden strain, ORF3 is absent. Sapoviruses are highly heterogeneous and based on phylogenetic analyses of amino acids of VP1 be divided into 19 genogroups of which viruses from GI, GII, GIV and GV infect humans and can be further subdivided into at least 17 genotypes. A pairwise distance cut-off value of ≤0.169 is used to distinguish different sapovirus genotypes and ≤0.488 to distinguish different genogroups (Oka et al., 2015). Viruses in the other genogroups have been detected in swine (GIII and GV-GXI), sea lions (GV), mink (GXII), dogs (GXIII), bat (GXIV, GXVI-GXIX) and rats (GXV) (Yinda et al., 2017). 

Biology 

None of the human sapoviruses can be propagated in cell culture. However, porcine enteric calicivirus, which is the reference strain for GIII sapoviruses, can be grown in porcine kidney cells as long as the media is supplemented with bile salts to induce intracellular signals to permit virus replication (Chang et al., 2004). Gastrointestinal infections caused by sapovirus most commonly occur in children under the age of 5 years but outbreaks in adults have been reported as well.

Species demarcation criteria

Not defined as there is only one species in the genus. The prototype strain for the species is Sapporo virus.

Related, unclassified viruses

Virus names and virus abbreviations are not official ICTV designations.