1. BACKGROUND
Seneca Valley virus (SVV) is a causative agent of vesicular disease (VD) in swine and belongs to the genus Senecavirus within the family of Picornaviridae (International Committee on Taxonomy of Viruses, 2017). SVV is a non-enveloped, single-stranded, positive-sense RNA virus (Maggioli et al., 2018). The genome of SVV is approximately 7.3 kb in length and includes a 5’-untranslated region (UTR), a 3’-UTR, and an open reading frame (ORF) encoding the lead protein, four structural proteins (VP1, VP2, VP3 and VP4), seven non-structural proteins (2A, 2B, 2C, 3A, 3B, 3C and 3D), thus forming the standard ‘L-4-3-4’ structural layout that is typical of the Picornaviridae family (Hales et al., 2008, Leme et al., 2017). SVV was first reported as a cell contaminant in 2002 and was named after SVV-001 (Hales et al., 2008). SVV-001 was used as a drug for the treatment of cancer because it exhibits a strong cytotoxic effect on small-cell lung cancer and other neurosecretory tumors (Reddy et al., 2007, Schenk et al., 2020). From a clinical perspective, it is very difficult to differentiate cases of swine infected with SVV from other causative agents of porcine idiopathic vesicular disease (PIVD), such as food-and-mouth disease virus (FMDV), swine vesicular disease virus (SVDV), vesicular exanthema of swine virus (VESV) and vesicular stomatitis virus (VSV) (Leme et al., 2017).
The infection of swine with SVV was first confirmed in Canada in 2007 (Pasma et al., 2008, Leme et al., 2017). Since then, porcine SSV cases have also been detected in America, China, Brazil, Columbia, Thailand and Vietnam (Leme et al., 2016, Sun et al., 2017, Saeng-Chuto et al., 2018a, Arzt et al., 2019). In China, SVV was first reported in Guangdong province in 2015; subsequently, SVV was detected in populations of swine in Hubei, Fujian, Henan, Heilongjiang, Guangxi Province and Shandong Province (Wu et al., 2016, Wu et al., 2017, Chen et al., 2018, Liu et al., 2019, Bai et al., 2020)). In 2018, the China Animal Health and Epidemiology Center performed a retrospective surveillance study for SVV between 2016 and 2018; the proportion of swine infected with SVV in 2016, 2017, and 2018 were 14.6% (7/48), 21.9% (7/32) and 22.6% (19/84), respectively (Zhang et al., 2019). The gene sequences for these viruses can be obtained from GenBank and can be classified into three clades; clade I is the first identified strain of SVV virus, including SVV-001, clade II is SVV strains of US identified from 1988 to 1997, and clade III contains SVV strains from Brazil, Canada, China, Thailand and the United States from 2001 to 2019; and most of the sequences are concentrated in clade Ⅲ (Leme et al., 2017). The sequences of SVV in clade Ⅲ can be clustered into four groups according to the country of origin (Xu et al., 2017). In this manuscript, we report a new strain of SVV that was isolated from Guangxi Province in China and describe the genetic characteristics of this new strain.