Canine parvovirus in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Veterinary Studies in Virology at Massey University, Turitea, Palmerston North, New Zealand
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Date
2013
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Massey University
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Abstract
Since the initial global emergence of canine parvovirus type 2 (CPV-2) in the early 1980s the
virus has continued to evolve in its new host. As a result, the original CVP-2 was replaced by
newly emerged subtypes designated CPV-2a and CPV-2b. Recently, a third antigenic subtype
CPV-2c has emerged in several countries. In New Zealand the evolution of CVP-2 has not
been monitored since its emergence in the early 1980s, largely because of the high efficacy of
the vaccines available on the market. This lack of monitoring of CPV-2 has left a dearth of
knowledge regarding the epidemiological features of CPV-2 in New Zealand. Hence, the aim
of this study was to determine what subtypes of CPV-2 circulate in New Zealand and to
investigate the phylogenetic relationships between CPV-2 from New Zealand and from other
parts of the world.
As part of this project, a virological survey was conducted across New Zealand. A total of 79
faecal samples were collected from dogs suspected to be infected with CPV-2, as judged by
submitting veterinarians. Of those, 70 tested positive for CPV-2 DNA. All but one of the
CPV-2 sequences were subtyped as CPV-2a. The remaining sequence was subtyped as CPV-
2, and most likely represented a vaccine strain of the virus. The majority (74.3%) of CPV-2
positive samples originated from dogs six months of age and younger, with 70% of samples
collected from dogs considered not fully vaccinated (unvaccinated dogs or those with only
single vaccination), a further 17% of samples originated from dogs with an unknown
vaccination history.
Two separate phylogenetic analyses were performed. Seventy one CPV-2 positive sequences
originated from New Zealand (61 survey samples, six historic samples, two vaccine
sequences and one parvovirus sequence obtained from a cat) and the reference sequence were
trimmed to produce contiguous sequences of equal length. These 72 sequences were used to
investigate the genetic structure of CPV-2 within New Zealand. Haplotype network analyses
revealed that Cook-straight [i.e. Cook Strait] is not an effective geographical barrier to CVP-2 gene flow with
an equal distribution of genotypes in the North and South Islands. Translocation of the virus
between the islands is likely occurring by transportation of sub-clinically infected animals and
fomites.
Additional CPV-2 VP2 sequences (n=95) originating from various countries were obtained
from the National Centre for Biotechnology Information (NCBI) database. The selection of 27
samples originating from New Zealand for which a full length contiguous sequence of VP-2
gene was available were aligned with sequences obtained from the NCBI database. The
resulting dataset of 123 CPV-2 sequences was used to assess the New Zealand CPV-2
sequences in the context of the worldwide radiation of CPV-2. Phylogenetic analyses of this
dataset revealed that New Zealand has a closed monophyletic population of CPV-2 sequences.
This suggests that CPV-2 is not being continuously introduced to New Zealand from
overseas, but has evolved following a limited number of introductions in the past.
Phylogenetic analysis also revealed that CPV-2 subtypes from around the world have
emerged independently of one another.
This work has contributed to our understanding of molecular epidemiology of CPV-2 in New
Zealand. The knowledge of predominant CPV-2 subtypes circulating in this country is
important for evidence driven recommendations with regard to CPV-2 vaccination.
Understanding of the genetic structure of the current CPV-2 circulating in New Zealand is
also crucial for timely recognition, detection and management of any novel antigenic subtypes
that may emerge in the future.
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Keywords
Canine parvovirus, Dog diseases, Infectious diseases in dogs, Molecular epidemiology, Research Subject Categories::VETERINARY MEDICINE::Veterinary epidemiology