3.3 Phylogenetic analysis of SVV in China
Genetic analysis, based on the complete sequences of SVV, revealed that the Chinese isolates of SVV were mainly grouped into three clusters (clusters 1-3), thus indicating the complexity and sequence diversity of these strains. CH-GX-01-2019, was classified into cluster 3 and belonged to one branch of the CH/GXI09/2016 strain (KY038016.1). CH-GX-01-2019 shared 96.7% nucleotide identity to the first reported strain in China (CH-01-2015; KT321458). The homologies of the nucleotide sequence for CH-GX-01-2019 with cluster 1, cluster 2 and cluster 3 of the Chinese strains were 96.0 - 96.5%, 96.1 - 96.8% and 98.2 - 98.7%, respectively (Fig. 2A) . Surprisingly, CH-GX-01-2019 showed the highest similarity (98.9%) with the 2018 Vietnam strain (MH704432.1).
With regards to the VP1 sequence of SVV, the Chinese isolates of SVV were mainly grouped into three genetic clusters (clusters 1 - 3). The homologies of CH-GX-01-2019 with cluster 1, cluster 2 and cluster 3 of the Chinese strains were 95.3 - 95.7%, 94.2 - 96.1% and 97.7 - 98.5%, respectively. Variations in the VP1 amino acid sequence were generally observed at codons 230 (T/I) and 231 (A/S); these changes were critical to the variations observed between the different viruses (Fig. 2B) .