Haemorrhagic kidney syndrome (HKS), a serious disease affecting Atlantic salmon on the east coast of Canada, was determined to be caused by infectious salmon anaemia virus (ISAV) through the isolation of the pathogen on the SHK-1 (salmon head kidney) cell line and confirmation by ISAV-specific immunofluorescent antibody test (IFAT) and reverse transcriptase polymerase chain reaction (RT-PCR). In addition, the defining histopathology of HKS could be reproduced following the injection of material that rendered challenged fish ISAV-positive by cell culture in the absence of any other detectable pathogen. Preliminary nucleotide sequence comparison does not suggest any direct epidemiological connection between the Canadian and Norwegian isolates.

Nodaviruses (NNV) are responsible for causing disease outbreaks mainly in hatcheryreared larvae and juveniles of a wide variety of fishes throughout the world. This disease has seriously limited the culture of marine fishes over the last decade. In the Atlantic provinces of Canada, disease caused by a nodavirus was first reported in juvenile Atlantic cod being reared in Nova Scotia, in 1999. More recently, disease outbreaks caused by nodavirus have been identified in hatcheryreared Atlantic cod and haddock in Newfoundland and New Brunswick, respectively, and along the east coast of the USA. The presence of NNV in wild Atlantic cod adults and wild winter flounder has also been reported. Nodaviruses were isolated from cultured Atlantic cod and haddock, as well as from wild winter flounder from a variety of geographical localities, and their virus coat (capsid) protein genes were partially sequenced. An analysis of the data indicates that all of the nodaviruses isolated from eastern North America were closely related to one another, but that they were distinct from the European isolates already sequenced. Regardless of host species, isolates from close geographical localities were more similar than those from distant geographical areas. At the protein level, differences in coat protein sequences were seen only for strains isolated from Atlantic cod originating from Newfoundland. Our results suggest that NNV may have been present in the Atlantic off Canada and on the east coast of the USA for some time, and has evolved to form a monophyletic group, distinct from other isolates found in cold-water species. Non-lethal methods for detection of NNV are necessary to develop management strategies for this disease, and would be an asset to diagnosticians and producers. Based on the results of this study, new primers were designed and developed for an improved RT-PCR assay able to detect North Atlantic nodaviruses in ovarian fluids, eggs and other tissues. The application of this test to field samples is discussed. KEY WORDS: Nodaviruses · RT-PCR · Phylogenetic analysis · Atlantic cod · Haddock Resale or republication not permitted without written consent of the publisherDis Aquat Org 62: [181][182][183][184][185][186][187][188][189] 2004 der (Pleuronectes americanus) has been reported from Atlantic Canada (Barker et al. 2002, Cusack 2002. Nodavirus infection has been reported in cultured juveniles of Atlantic cod from the UK, with low mortality rates (approximately 2%) observed over a 3-mo period (Starkey et al. 2001).Nodaviruses are small non-enveloped viruses, and their genome consists of 2 sense RNA strands. RNA1 (3.1 kb) of striped jack NNV encodes a putative RNAdependent RNA polymerase (RdRp) and RNA2 (1.4 kb) encodes the capsid protein precursor (Mori et al. 1992). To date, comparisons between the nucleotide sequences of a variable region of the capsid protein referred to as T4 (Nishizawa et al. 1994) have led to the division of the genus Betanodavirus into 7 type species: barfin flounder nervous necros...

No abstract

Infectious salmon anemia virus (ISAV) was isolated from farmed Atlantic salmon Salmo salar associated with an outbreak of hemorrhagic kidney syndrome in the Bay of Fundy, Canada. The virus induced cytopathic effects in salmon head kidney cell line SHK-1 from Atlantic salmon and was positively confirmed as ISAV by an indirect fluorescent antibody test and by reverse transcriptase polymerase chain reaction. Atlantic salmon parr injected with ISAV from the SHK-1 line experienced significant reductions in hematocrits as early as 5 d postinfection (DPI). Mortality began 17 DPI and reached 76% by 24 DPI at a water temperature of 11ЊC. In a second trial, similarly high mortality occurred in salmon parr injected with 10-fold dilutions of supernatant from ISAV-infected SHK-1 cultures. The ISAV was reisolated from eight randomly selected salmon that died after experimental infection. Microscopic pathological changes among infected fish included congestion and necrosis, seen in the livers from 7 of 19 samples and in the kidney from 1 of 18 salmon examined. Other tissues affected included gill, intestine, and pyloric caeca. The absence of microscopic lesions in the remaining experimentally infected fish could not be explained. Further studies are therefore needed to better understand the factors contributing to pathological changes after natural or experimental infection.

A large-scale mortality of larval and juvenile halibut Hippoglossus hippoglossus occurred at a semi-commercial halibut farm in Atlantic Canada. Investigation of the cause revealed aquareovirus particles in necrotic liver tissue of affected fish. Cytopathic effect on CHSE-214 cell lines occurred from all fish cultured for viruses, and the viral morphology of the particles in culture was consistent with that observed in necrotic host tissue. The virus was placed in the family of Reoviridae, genus Aquareovirus based on morphology and RT-PCR results. Multifocal hepatocellular necrosis was a consistent finding in all fish as well as acute necrosis of proximal renal tubules. Concurrent bacterial infections were present in some specimens. Fish experimentally treated with oxytetracycline or a combination of oxytetracycline and chloramine-T had a significantly lower mortality rate than untreated fish. Fish treated with chloramine-T alone had a significantly elevated mortality rate compared to controls. Despite supportive medical therapy, mortality levels in treated and untreated groups remained elevated, supporting the hypothesis that the primary pathogen was of viral origin. This is the first report of elevated mortalities in Atlantic halibut associated with an aquareovirus.