Isolation and sequence analysis of the complete NS1 and VP2 genes of canine parvovirus from domestic dogs in 2013 and 2014 in China

Canine parvovirus (CPV) can cause severe disease in animals and continuously generates new variant and recombinant strains in dogs that have a strong impact on sanitation. It is therefore necessary to investigate epidemic CPV strains to improve our understanding of CPV transmission and epidemic behavior. However, most studies have focused on the analysis of VP2, and therefore, information about recombination and relationships between strains is still lacking. Here, 14 strains of CPV were isolated from domestic dogs suspected of hosting CPV between 2013 and 2014 in China. The complete NS1 and VP2 genes were sequenced and analyzed. The results suggest that the new CPV-2a and new CPV-2b types are the prevalent strains in China. In addition to a few mutations (residues 19, 544, 545, 572 and 583 of NS1 and residues 267, 370, 377 and 440 of VP2) that were preserved during transmission, new mutations (residues 60, 630 of NS1, and residues 21, 310 of VP2) were found in the isolated strains. A phylogenetic tree based on VP2 sequences illustrated that the new CPV-2a and new CPV-2b strains from China form single clusters that are distinct from lineages from other countries. Moreover, recombination between the new CPV-2a and new CPV-2b types was also identified in the isolated strains. Due to differences in selection pressures or recombination, there were a small number of inconsistencies between the phylogenetic trees for VP2 and NS1, which indicated that phylogenetic relationships based on VP2 might not be representative of those based on NS1. The data indicated that mutations and recombination are constantly occurring along with the spread of CPV in China.