Canine respiratory viruses in New Zealand dogs : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand
Loading...
Date
2019
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
Acute infectious tracheobronchitis (ITB) is an important health issue in dogs worldwide. It
predominantly affects kenneled dogs but has also been described in pet dogs. The aetiology of the disease is complex and likely to involve various respiratory pathogens, as well as host- and environment-related factors. Traditionally, canine parainfluenza virus (CPiV), canine adenovirus type 2 (CAdV-2), and Bordetella bronchiseptica were regarded as most commonly involved in canine ITB, and are incorporated into available vaccines. Other
bacterial species as well as canine herpesvirus type 1 (CHV-1), canine reoviruses, and canine distemper virus have also been detected in the samples from diseased dogs. Within the past two decades, several novel canine respiratory viruses that may contribute to canine ITB have been discovered. These include canine influenza viruses, canine respiratory
coronavirus (CRCoV), canine pneumovirus CnPnV), canine bocavirus, and canine hepacivirus. It appears that the contribution of various respiratory pathogens to canine ITB differs between different geographical locations and hence, the availability of local data is important for the implementation of the most appropriate disease prevention strategies. To date, very little data are available on the respiratory pathogens circulating among dogs in New Zealand. As such, the objective of the present study was to identify what viruses circulate among local dog populations including determination of the presence/absence of the recently identified canine respiratory viruses and to determine which of these pathogens are likely to be aetiologically involved in canine ITB. The second objective was to characterise at the molecular level selected novel viruses identified. In order to identify viruses associated with canine ITB, metagenomic shot-gun sequencing approach was used to determine what viral nucleic acids were present in the pooled samples prepared from oropharyngeal swabs collected from dogs with clinical signs of ITB
(n = 50) and from healthy dogs (n = 50). Following shot-gun sequencing, assembly and mapping, sequences of CHV-1, CRCoV, CnPnV, canine picornavirus and influenza C virus were identified in the pooled sample from dogs with ITB, while none of these sequences were identified in the pooled sample from healthy dogs. This is the first molecular
identification of CnPnV, CRCoV, CanPV and influenza C virus in the New Zealand dog population. Real-time PCR assays were then designed to assess the frequency of detection of five
canine respiratory viruses (CPiV, CAdV-2, CHV-1, CRCoV and CnPnV) in individual oropharyngeal swab samples from dogs with signs of ITB and from healthy dogs. Infections with at least one canine respiratory virus were more commonly detected in dogs with signs of ITB (21/56 (37.50 %)) than in healthy dogs (15/60 (25.00 %)). Dogs with signs of ITB were most commonly positive for CnPnV (26.78 %) followed by CAdV-2 (8.92 %), CPiV (3.57 %), CHV-1 (3.57 %), and CRCoV (1.78 %). Only CnPnV (23.33 %) and CAdV-2 (5.00 %) were identified in samples from healthy dogs. The overall prevalence of CnPnV in the sampled population was 29/116 (25.00 %). This research revealed the first molecular evidence for the presence of CRCoV and CnPnV in dogs in New Zealand. As such, these viral sequences were further analyzed. The attachment gene (G) of three CnPnVs (CnPnV NZ-007, CnPnV NZ-048 and CnPnV NZ-049) was sequenced to characterise CnPnV circulating among dogs in New Zealand. Sequence analysis of the CnPnV G gene revealed that both group A and group B subtypes of CnPnV circulate in New Zealand. The genetic analysis of the 3‘ genomic region of CRCoV from New Zealand (CRCoV NZ-046/16) revealed closer relation to the British CRCoV 4182, Italian CRCoV 240/05 and Chinese CRCoV BJ232 than to the Korean CRCoVs (K9, K37 and K39). A deletion of one nucleotide at the region between the genes encoding the spike protein and 12.8 kDa accessory protein in CRCoV NZ-046/16 resulted in deletion of a stop codon with subsequent translation of predicted 5.9 kDa and 2.7 kDa proteins instead of two accessory proteins (4.9 kDa and 2.7 kDa) encoded at that region by most other CRCoVs. In order to gain some insight into the epidemiology of CRCoV among dogs in New Zealand, canine sera (n = 100) were randomly selected from diagnostic laboratory submissions on a monthly basis from March to December 2014, and analyzed for the
presence of CRCoV antibodies using a commercial blocking ELISA with bovine coronavirus antigen. Overall, 53 % of 1015 sera tested were positive for CRCoV antibody. The present study revealed an increase in the prevalence of CRCoV antibodies with age (p = 0.014). The work presented in this thesis has contributed to our understanding of the viruses involved in canine respiratory disease in New Zealand. Although infections with CPiV, CAdV-2, and CHV-1 were detected, it appeared that recently discovered canine respiratory viruses, including CRCoV and CnPnV, may also play an important role in canine ITB in New Zealand. This may provide one explanation for the development of respiratory disease in some fully vaccinated dogs, as anecdotally reported by field veterinarians. If so, their potential role and local epidemiology should be investigated in future studies.
Description
Figures are in the public domain or re-used with permission.
Keywords
Respiratory infections, Dogs, Virus diseases, New Zealand