Sapelovirus A (SV-A) is a positive-sense single-stranded RNA virus which is associated with acute diarrhea, pneumonia and reproductive disorders. The virus capsid is composed of four proteins, and the functions of the structural proteins are unclear. In this study, we expressed SV-A structural protein VP1 and studied its antigenicity and immunogenicity. SDS-PAGE analysis revealed that the target gene was expressed at high levels at 0.6 mM concentration of IPTG for 24 h. The mouse polyclonal antibody against SV-A VP1 protein was produced and reached a high antiserum titer (1: 2,048,000). Immunized mice sera with the recombinant SV-A VP1 protein showed specific recognition of purified VP1 protein by western blot assay and could recognize native SV-A VP1 protein in PK-15 cells infected with SV-A by indirect immunofluorescence assay. The successfully purified recombinant protein was able to preserve its antigenic determinants and the generated mouse anti-SV-A VP1 antibodies could recognize native SV-A, which may have the potential to be used to detect SV-A infection in pigs.

Conventionally, Porcine sapelovirus (PSV) has been considered to comprise a single geno- type, PSV-1; however, a potentially novel member of PSV was recently discovered. In the present study, we propose a genotype definition of PSV based on phylogenetic and genetic analyses of the polyprotein, P1, and VP1 genes of available PSV sequences. Two genotypes, with pro- posed names PSV-1 and PSV-2, were identified. Moreover, the cut-off values (number of diffe- rences per site between amino acid sequences) for the definition of genotypes were established to be 0.1115 (polyprotein), 0.176 (P1), and 0.272 (VP1). The findings of this study are expected to enrich knowledge of PSV classification.