Analysis of canine parvoviruses circulating in Australia reveals
predominance of variant 2b strains and identifies feline parvovirus-like
mutations in the capsid proteins
Abstract
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.