In Europe, 2 closely related alphaviruses (Togaviridae) are regarded as the causative agents of sleeping disease (SD) and salmon pancreas disease (SPD): SD virus (SDV) has been isolated from rainbow trout Oncorhynchus mykiss in France and the UK, while SPD virus (SPDV) has been isolated from salmon Salmo salar in Ireland and the UK. Farmed salmonids in western Norway also suffer from a disease called pancreas disease (PD), and this disease is also believed to be caused by an alphavirus. However, this virus has not yet been characterised at the molecular level. We have cultured a Norwegian salmonid alphavirus from moribund fishes diagnosed with cardiac myopathy syndrome (CMS) and fishes diagnosed with PD. The virus has also been found in salmon suffering from haemorrhagic smolt syndrome in the fresh water phase. The genomic organisation of the Norwegian salmonid alphavirus is identical to that in SPDV and SDV, and the nucleotide sequence similarity to the other 2 alphaviruses is 91.6 and 92.9%, respectively. Based on the pathological changes, host species and the nucleotide sequence, we suggest naming this virus Norwegian salmonid alphavirus (NSAV). Together with SPDV and SDV it constitutes a third subtype of salmonid alphavirus (SAV) species within the genus Alphavirus, family Togaviridae. KEY WORDS: Norwegian salmonid alphavirus · Virus characterisation · Pancreas disease Resale or republication not permitted without written consent of the publisherDis Aquat Org 66: [113][114][115][116][117][118][119][120] 2005 pers. obs., Poppe & Rimstad 1989). Alphavirus spp. have also been found, using RT-PCR and sequencing, in moribund farmed salmon in Norway diagnosed with cardiac myopathy syndrome, CMS (A. Nylund pers. obs.) and in salmon suffering from haemorrhagic smolt syndrome (HSS) in the fresh water phase (Nylund et al. 2003).The majority of cases in which Alphavirus spp. have been detected associated with disease in salmon and rainbow trout have been in Hordaland and Sogn og fjordane (western Norway), but recently a few cases have been seen in northern Norway (Nordland, Troms and Finnmark) (A. Nylund pers. obs.). The genomes of the viruses from northern Norway have been partially sequenced and are identical to those from western Norway. This means that Alphavirus spp. have been found in the majority of Norwegian counties with salmon farming.The complete genomes of SPDV from Ireland (Isolate F93-125) and SDV from France (Isolate S49P) have been sequenced and consist of about 12 kb (Weston et al. 2002). No other isolates have been completely sequenced, but partial sequencing of selected nonstructural and structural protein genes indicate that SPDV and SDV from the UK are identical to those sequenced from Ireland and France, respectively . Included in the studies by Weston et al. (2002Weston et al. ( , 2003 are also 2 Norwegian alphavirus isolates, PD97-N2 and PD97-N3 (supplied by K. E. Christie, Intervet, Bergen), originating from diseased salmon and rainbow trout, respectively. Both isolates were partia...

In the present study, 24 smolt production sites were screened for the presence of infectious salmon anaemia virus (ISAV) with the help of a specific real-time RT PCR assay, and 22 of these sites had smolts that were positive. If these smolt production sites are representative for the prevalence of ISAV in Norwegian smolts, then most marine production sites must be considered to be positive for ISAV. In addition, 92 European ISAV isolates have been genotyped based on the hemagglutinin-esterase gene (HE), and their distribution pattern was analysed. This pattern has been coupled to information about the origin of smolt, eggs, and broodfish in those cases where it has been possible to obtain such information, and with information about ISAV in neighbouring farms. The pattern suggests that an important transmission route for the ISAV could be that the salmon farming industry in Norway is circulating some of the isolates in the production cycle, i.e. some sort of vertical or transgenerational transmission may occur. It has also been shown that avirluent ISAV isolates are fairly common in Norwegian farmed salmon. Based on this, it is hypothesized that the change from avirulent to virulent ISAV isolates is a stochastic event that is dependent on the replication frequency of the virus and the time available for changes in a highly polymorphic region (HPR) of the HE gene to occur. This, and the possibility that only avirluent ISAV isolates are vertically transmitted, may explain why ISA most often occurs at marine sites and why no more than about 15 farms get ISA every year in Norway.

Diagnosis of SAV infections has traditionally been based upon clinical observations together with a set of histopathological findings in exocrine pancreas, heart and skeletal muscle, but recently, real-time RT-PCR assays have been developed as a supplement for the detection of SAV. The aim of this study was to determine tissue tropism of SAV1 and SAV3 in Atlantic salmon Salmo salar L. in order to identify the most suitable tissues for real-time RT-PCR diagnostic assays. The results indicated that the pseudobranch and the heart (ventricle) are the most useful tissues for such assays, regardless of disease status. The pyloric caecae with associated pancreatic tissue is unsuitable for diagnosis using this method. The use of real-time RT-PCR enabled viral RNA detection at all stages of the disease, including in surviving fish six months after infection. Considering the short production cycle of farmed salmonids, this suggests that surviving Atlantic salmon may become life-long asymptomatic carriers of SAV after an infection.

Hepatocyte nuclear factor-1alpha (HNF-1alpha) is a homeodomain-containing transcription factor regulating the expression of liver and pancreas-specific genes. Mutations in the HNF-1alpha-encoding gene TCF1 cause maturity-onset diabetes of the young, type 3 (MODY3). These mutations may affect nuclear import or reduce the ability of HNF-1alpha to stimulate transcription. We performed a functional dissection of HNF-1alpha, attempting both to define its nuclear localization signals (NLSs) and to identify important elements of the Cterminal transactivation domain. Three HNF-1alpha regions, A (amino acids 158-171), B (197-205), and C (271-282), highly similar to consensus NLSs, were studied by immunolocalization in HeLa cells. Region B could be identified as the most critical for correct nuclear localization. Deletion of two subregions (amino acids 398-470 and 544-631, respectively) in the HNF-1alpha C-terminal transactivation domain, resulted in the greatest reduction in stimulation of transcription compared to wild-type protein. However, this domain probably consists of many elements that work in concert to give the full transactivation potential of the protein.

Disease associated with salmonid Alphavirus (SAV) infection is a significant problem for farm production of salmonids in Europe. The SAV subtype 3 (SAV3) is a Norwegian subtype present exclusively in production systems for Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss in western Norway. It has been suggested that SAV3 is transmitted through smolt transport from the main area for SAV disease in western Norway to as far as northern Norway. One explanation for this type of spread is that SAV is present at freshwater production sites for Atlantic salmon smolts. The present study confirms this, showing that SAV3 is present at smolt production sites in Norway. At two sites in northern Norway that had received eggs from broodfish companies in Hordaland County, western Norway, 2-4-g fry were positive for SAV3. Hence, it cannot be excluded that vertical transmission could have contributed to the presence of SAV3 in northern Norway. In the present study, we followed the normal production cycle for Atlantic salmon in a fish farming company in Hordaland County. Twelve of 353 broodfish in study 1 and 28 of 31 broodfish in study 2 were found to be carriers of SAV3. In the same two studies, SAV was also detected in eggs (1 of 220), eyed eggs (3 of 270), and fry (6 of 600). The SAV was not detected in parr, smolts, or postsmolts, but after a year at sea the fish developed SAV disease. Given the difficulties in tracing the virus through the production cycle until development of SAV disease in the marine farm, we cannot draw any firm conclusions about whether vertical transmission occurs in Norwegian salmon production, and we cannot exclude the possibility that the development of SAV after 1 year at sea was caused by horizontal transmission rather than vertical transmission.