Summary
Canine parvovirus type 2 (CPV-2) is a small, single-stranded DNA virus
causing fatal hemorrhagic enteritis in dogs. Currently, CPV-2 has been
classified into CPV-2a, CPV-2b, and CPV-2c based on genetic variation in
the VP2 gene. The CPV-2c variant has become ubiquitous worldwide and
gained attention for monitoring parvoviral evolution. In this study, we
characterized the full-length genome sequences of CPV-2c isolates
obtained from 59 dogs in Vietnam. Molecular analysis revealed that
Vietnamese CPV-2c shared a common evolutionary pattern with the Asian
CPV-2 clade, which is marked by genetic signature patterns in the
structural and nonstructural proteins. In addition, these Vietnamese
CPV-2c strains exhibited unique Thr112Ile and Ile447Met mutations in the
VP1 and VP2 sequence, respectively. Interestingly, phylogenetic analysis
indicated that the mutations of amino acid residues in both the
structural and nonstructural genes have contributed to the emergence of
a new clade, designated here as the Asia-IV clade. The substitution
rates, estimated from a dataset containing 199 sequences over the last
40 years, confirmed that CPV-2 showed
a high rate of nucleotide
substitution, at about 2.49 x 10-4 nucleotide
substitutions per site per year (nt/s/y), with VP1/2 and NS1/2 estimates
of 3.06 x 10-4 and 3.16 x 10-4nt/s/y, respectively. Even though no evidence of genetic recombination
in these Vietnamese CPV-2c strains was established, potential positive
selection sites were observed in both the structural and nonstructural
genes, suggesting the viral evolutionary process has occurred in both
the structural and nonstructural proteins. Genetic and evolutionary
analysis of the full-length genome sequence is necessary to gain
evolutionary insight of CPV-2. Further studies are needed to elucidate
the potential role of these observed mutations in the novel Asia-IV
clade.
Keywords: Asia-IV subclade, canine parvovirus-2c, dog,
evolution, phylodynamic, Vietnam