Molecular characterization of canine parvovirus type 2(CPV2)reveals a high prevalence of the CPV2c genotype among dogs sufering from diarrhea

Canine parvovirus 2(CPV-2)is a highly contagious virus in dogs that typically causes hemorrhagic enteritis and a high mortality rate in unvaccinated puppies.The genetic variability and antigenic diversity of CPV-2 hinder its efective prevention of infection by vaccination.To investigate the epidemiology and genetic characteristics of CPV-2 in China,rectal swabs from afected dogs were collected from diferent animal clinics in Kunshan from 2022 to 2023.Preliminary detection and capsid gene sequencing of CPV-2 were performed using previously described primers and protocols.The overall detection rate for CPV-2 was 16.5%(33/200).A signifcant association was found between the CPV-2-positivity and clinical signs,age,breed and vaccination status.Sequence analysis revealed the presence of CPV-2c genotypes in all positive samples,which were genetically similar to other Asian CPV-2c strains.Notably,four key mutations(A5G,F267Y,Y324I and Q370R)were detected in all isolates,and one novel mutation(I447M)was detected in three CPV-2 isolates.These mutations in the CPV-2 strains could impact vaccine efcacy and the efectiveness of the virus immune evasion.Surprisingly,no recombination events were observed between the identifed CPV-2c strains and reference strains from China.Our data revealed that amino acid residues 324,426 and 440 of VP2 may under strong selection pressure.This pattern of genetic variation in the CPV-2 lineage warrants continuous laboratory-based surveillance programs in other parts of China to better understand the pattern of seasonal distribution and association between emerging genotypes and the intensity of disease severity.