Summary
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 acquired
amino-acid (aa) mutations in key capsid residues, associated with
biological and/or antigenic changes. This study aimed to identify and
analyse CPV variants and their capsid mutations amongst Australian dogs,
to gain insights into the evolution of CPV in Australia 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.