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Emily Kwan

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Canine parvovirus (CPV) is a major enteric pathogen of dogs worldwide that emerged in the late 1970s from a feline parvovirus (FPV)-like ancestral virus. Shortly after its emergence, variant CPVs were generated by acquiring amino-acid (aa) mutations in key capsid residues, associated with biological and/or antigenic changes. This study aimed to identify CPV variants amongst Australian dogs, to gain insights into the evolution of CPV in Australia through phylogenetic analysis of these variants, and to investigate relationships between the disease and vaccination status of dogs from which isolates were collected. CPV VP2 sequences were amplified from 79 faecal samples collected from dogs with parvoviral enteritis at 20 veterinary practices in 5 Australian states. The median age at diagnosis was 4 months (range 1 to 96 months). Only 3.7% of dogs with vaccination histories had completed recommended vaccination schedules, while 49% were incompletely vaccinated and 47.2% were unvaccinated. For the first time, CPV-2b has emerged as the dominant antigenic CPV variant circulating in dogs with parvoviral enteritis in Australia, comprising 54.4% of strains, while CPV-2a and CPV-2 comprised 43.1% and 2.5% of strains. CPV-2c strains were not identified. Analysis of translated VP2 sequences revealed a vast repertoire of aa mutations. Several Australian CPV strains displayed signatures in the VP2 protein typical of Asian CPVs, suggestion introduction of CPV strains from Asia, and/or CPV circulation between Asia and Australia. Strains of CPV were identified containing aa residues typical of FPV at capsid (VP2) key positions, representing reverse mutations or residual mutations retained from CPV-2 during adaptation from an FPV-like ancestor, suggesting that evolutionary intermediates between CPV-2 and FPV are circulating in the field. Similarly, intermediates between CPV-2a-like viruses and CPV-2 were also identified. These findings help inform a better understanding of the evolution of CPV in dogs.