3.2 Similarity of the full-length genome, nucleotide and amino acid sequence of NS and VP regions of Vietnamese CPV-2c
The complete full-length genetic sequences of various Vietnamese CPV-2, ten CPV-2c (HN04, HN06, HN07, HN08, HN30, DN01, DN02, HCM01, HCM03, and HCM09) and one CPV-2a (HCM16) strains were selected for sequencing using multiple primer pairs for parvovirus to cover the whole genome. The obtained full-length genome sequences of the Vietnamese CPV-2 variants were submitted to GenBank (accession nos. MT106228–38). Sequence analysis showed that the Vietnamese CPV-2c strains were highly similar among strains, ranging from 99.5–99.8% in nucleotide similarity (Table 1, Supplementary Table S3a). Neither nucleotide differences nor specific amino acid mutations were evident among the Vietnamese CPV-2c strains detected from different geographic regions.
The complete genomes of the Vietnamese CPV-2c strains from this study were found to be closely related to the recently isolated (in 2017) Italian CPV-2c strain (MF510157) and the Chinese CPV-2a strain (KR002800) isolated in 2014, with 99.6–99.8% and 99.3–99.5% nucleotide identity, respectively. Meanwhile, the Vietnamese CPV-2c strains were genetically distant from the previous Italian CPV-2c strain (KU508407) isolated in 2009 and the single Vietnamese CPV-2a variant isolated in this study, with 98.8–98.9% and 98.6–98.7% nucleotide identity, respectively (Table 1, Supplementary Table S3a).
In addition, the nucleotide and amino acid sequence of the NS region were similar between these Vietnamese CPV-2c strains, and the Italian CPV-2c (MF510157) and Chinese CPV-2a (KR002800) strains, ranging from 99.7–100% similarity (Table 1, Supplementary Table S3b). Meanwhile, there were different nucleotide and amino acid sequence similarities in the VP region, accounting for 99.4–99.6% and 99.5–99.7%, respectively, compared with MF510157, and 98.9–99.1% and 99.0–99.3%, respectively, compared with KR002800. Whereas the Vietnamese CPV-2c strains showed a lower degree of sequence similarity compared to KU508407 and the single Vietnamese CPV-2a strain from this study (Table 1, Supplementary Table S3c).