Continuing evolution of canine parvovirus in China: Isolation of novel variants with an Ala5Gly mutation in the VP2 protein

- This is the first report on isolation of novel CPV-2c from a dog in China.
- This study reveals that new CPV mutants are spreading in China.
- CPV vaccines failed to generate protection in vaccinated dogs In China.

Canine parvovirus (CPV) type 2c is a new antigenic variant of CPV-2. Since the year 2000 it has spread to several countries, causing severe hemorrhagic enteritis in dogs. In 2014 and 2015, 58 fecal samples were collected from dogs in Beijing with suspected CPV infection. Regardless of the vaccination status of the dogs, 43 samples were found positive for CPV according to PCR results; i.e., 18, 7, and 18 respectively belonged to antigenic types new CPV-2a, new CPV-2b, and CPV-2c. A phylogenetic tree based on their VP2 gene sequences indicated that the Chinese CPV-2c strains form a separate cluster. In addition to synonymous mutations, the CPV-2c strains also contain a unique coding mutation in VP2 that leads to glycine at residue 5, instead of the highly conserved alanine at this position in all other CPV-2c strains sequenced to date. Using F81 cells, several novel isolates of CPV-2c, each with the Ala5Gly mutation, were obtained. One of these was used to infect experimentally beagle dogs, which subsequently developed the typical clinical symptoms of CPV infection. Hence, it appears that CPV-2c is still evolving in China, a finding that warrants continuous surveying and the eventual adaptation of current vaccines.