Molecular Analysis of Full-Length VP2 of Canine Parvovirus Reveals Antigenic Drift in CPV-2b and CPV-2c Variants in Central Chile

SIMPLE SUMMARY: Canine parvovirus (CPV) is a relevant pathogen, mainly affecting unvaccinated puppies, causing severe and fatal disease. CPV is classified into three variants (CPV-2a, CPV-2b and CPV-2c), which are widely distributed worldwide. These variants may be mutated at specific sites relevant to the immune response against CPV in dogs, and thus previously characterized vaccines may not be effective against new mutants. Therefore, the aim of the present study was to perform a molecular characterization of CPV variants. For this purpose, blood samples from canine patients in central Chile were used. The results of this study showed that the circulating variants were mainly CPV-2c followed by CPV-2b. In addition, genetic mutations were found in regions important for the immune response against CPV, which possibly has implications for the protective immunity generated by available vaccines. ABSTRACT: Canine parvovirus (CPV) is a major pathogen in canines, with a high mortality rate in unvaccinated puppies. CPV is traditionally classified into three antigenic variants (CPV-2a, CPV-2b and CPV-2c) based on the amino acid sequence of the VP2 protein. Currently, various mutations are described in the receptor-binding area or in the regions of greatest antigenicity of the VP2 protein, giving rise to new viral variants that are capable of immunological escape, affecting the protective immunity of traditional vaccines. In the present study, a molecular characterization of the VP2 gene was performed, which included phylogenetic analysis, amino acid characterization and determination of selection pressures. Blood samples were initially collected from canine patients with clinical signs of gastrointestinal infection, of which 69 were positive for CPV as measured by means of PCR and 18 samples were selected for the amplification of the complete VP2 gene. The analysis revealed a higher rate of CPV-2c-positive patients compared to CPV-2b. Furthermore, the amino acid characterization of VP2 indicated mutations in the regions of highest antigenicity previously described in the literature (CPV-2b: 297 and 324; CPV-2c: 440), as well as others not previously documented (CPV-2b: 514; CPV-2c: 188, 322, 379, 427 and 463). Our analysis of selection pressure showed that the VP2 gene is under negative selection. However, positive selection point sites were identified, both in CPV-2c (324, 426 and 440) and CPV-2b (297 and 324), at sites that have been associated with evasion of the immune response via antigenic drift, which possibly has implications for the protective immunity generated by traditional vaccines.