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Detection of aquareovirus in farmed Tasmanian atlantic salmon (Salmo salar)


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Zainathan, SC 2012 , 'Detection of aquareovirus in farmed Tasmanian atlantic salmon (Salmo salar)', PhD thesis, University of Tasmania.

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This thesis focused on the detection and identification of Tasmanian Atlantic salmon
aquareovirus (TSRV), which is one of the few viral agents of Atlantic salmon endemic in
Tasmania. Due to the low pathogenicity and ubiquitous nature of TSRV, there has been little
interest in the significance of this virus. However, more recently, TSRV infections appeared
to be associated with diseased fish and concerns about the negative impact of infection with
this virus on aquaculture productivity have increased. Industry’s concerns regarding the
significance of TSRV have resurfaced and recent research has indicated that under certain
conditions TSRV could cause disease. Thus better management and control is being
considered by industry and regulators. Validation of diagnostic methods has been a major
focus in this thesis. Intra-laboratory and inter-laboratory comparison of PCR and virus
isolation on piscine cell lines were carried out to determine the most sensitive diagnostic
method, using tissues of farmed Atlantic salmon from various aquaculture sites around
Tasmania. A total of 144 fish from 9 sites (12-33 fish per site) were sampled from two
regions (Tamar River & South-east Tasmania) during late spring to early summer of 2009
and the data were analysed using different statistical approaches. This study demonstrated the
qPCR assay to be highly sensitive (95.2%) and highly specific (95.2%) for the detection of
TSRV. The prevalence of TSRV ranged from 6-22% in both regions. Following this, the use
of swabs in preference to organs as the sample collection method was evaluated for
individual and pooled samples. The use of swabs was shown to be best for field surveillance
and screening purposes when the only concern with the presence and absence of virus in the
population. The incidence of TSRV infections was investigated by undertaking a field
investigation at farm sites located in South-east Tasmania. Throughout this field
investigation, the incidence of TSRV infections was low (6.15%). The findings do not
exclude the role of TSRV in influencing the host’s susceptibility to other infections. Non
specific gross pathology and histopathological changes were observed in TSRV positive
salmon and similar observations were present in TSRV negative salmon. On the basis on
archival cases liver pathology has been identified as the predominant pathology caused by
TSRV. As a basis for a preliminary characterisation study, fourteen isolates of TSRV
originating from various locations in Tasmania, covering a 20-year period obtained from
various host species, host tissues and isolated on different cell lines, were selected in an
attempt to increase the probability of detecting virus variants. Typical and atypical variants of
TSRV were identified based on genotypic and phenotypic characterisation of the different
isolates. Electron microscopic examination demonstrated the existence of at least three
variants based on viral particle size. This study revealed preliminary evidence of vertical
transmission of TSRV from brood-stocks to eggs and horizontal transmission from farmed
salmon to wild fish. Finally, this characterisation study demonstrated the existence of at least
one variant TSRV isolate other than the more commonly isolated, typical TSRV in farmed
Tasmanian Atlantic salmon. The use of different detection/diagnostic methods in this thesis,
has improved the scope of the detection of TSRV.

Item Type: Thesis - PhD
Authors/Creators:Zainathan, SC
Keywords: detection, diagnostic method, TSVR
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