In February 2019, following the annual taxon ratification vote, the order Mononegavirales was amended by the addition of four new subfamilies and 12 new genera and the creation of 28 novel species. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV).

The emergence of infectious salmon anaemia virus (ISAV) in Canada and Scotland and frequent new outbreaks of the disease in Norway strongly suggest that there are natural reservoirs for the virus. The main host for the ISA virus is probably a fish occurring in the coastal area, most likely a salmonid fish. Since sea trout is an abundant species along the Norwegian coast, common in areas where ISA outbreaks occur, and possibly a life-long carrier of the ISA virus, a study was initiated to evaluate reverse transcriptase polymerase chain reaction (RT-PCR) for diagnosis of the virus in experimentally infected trout. Several tissues (kidney, spleen, heart and skin) were collected from the trout during a 135 d period. The following diagnostic methods for detection of the ISA virus were compared: cell culture (Atlantic Salmon Kidney, ASK cells), challenge of disease-free salmon with blood from the infected trout, and RT-PCR. The RT-PCR was the most sensitive of these methods. With the help of this technique it was possible to pick out positive individuals throughout the experimental period of 135 d. Challenge of disease-free salmon were more sensitive than cell culture (ASK cells). These 2 latter methods require use of the immunofluorescent antibody test (IFAT) or RT-PCR for verification of presence of ISA virus.

In March 2020, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. At the genus rank, 20 new genera were added, two were deleted, one was moved, and three were renamed. At the species rank, 160 species were added, four were deleted, ten were moved and renamed, and 30 species were renamed. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV.

The present study describes the use of molecular methods in studying infectious salmon anaemia virus (ISAV), an important pathogen of farmed salmon in Norway, Scotland, the Faeroe Islands, Canada, USA and Chile. The nucleotide sequences of the haemagglutinin gene (HA) from 70 ISAV isolates have been analysed for phylogenetic relationship and the average mutation rate of nucleotide substitutions calculated. The isolates constitute 2 major groups, 1 European and 1 North American group. The isolate from Chile is closely related to the North American isolates. The European isolates can be further divided into 3 separate groups reflecting geographical distribution, time of collection, and transmission connected with farming activity. Based on existing information about infectious salmon anaemia (ISA) and new information emerging from the present study, it is hypothesised that: (1) ISAV is maintained in wild populations of trout and salmon in Europe; (2) it is transmitted between wild hosts mainly during their freshwater spawning phase in rivers; (3) wild salmonids, mainly trout, possibly carry benign wild-type ISAV isolates; (4) a change (mutation) in virulence probably results from deletions of amino acid segments from the highly polymorphic region (HPR) of benign wild-type isolates; (5) ISA emerges in farmed Atlantic salmon when mutated isolates are transmitted from wild salmonids or, following mutation of benign isolates, in farmed salmon after transmission from wild salmonids; (6) farming activity is an important factor in transmission of ISAV between farming sites in addition to transmission of ISAV from wild salmonids to farmed salmon; (7) transmission of ISAV from farmed to wild salmonids probably occurs less frequently than transmission from wild to farmed fish due to lower frequency of susceptible wild individuals; (8) the frequency of new outbreaks of ISA in farmed salmon probably reflects natural variation in the prevalence of ISAV in wild populations of salmonids. KEY WORDS: Infectious salmon anaemia virus · ISAV · Maintenance · Reservoir · EpizooticsResale or republication not permitted without written consent of the publisher

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...