SAV

Salmon Alpha Virus (SAV) is considered a serious pathogen of farmed Atlantic salmon and rainbow trout in Europe. First identified in Ireland in 1995, it is closely associated with pancreas disease (PD) and the sleeping disease virus that have been isolated in cultured rainbow trout and Atlantic salmon in Europe and North america (Kent and Elston 1987). It has also been identified in the marine phase of production in Norweigan farmed Atlantic salmon. It is in the Alphavirus genus, within the family Togavirdae. There are currently six known subtypes of SAV; specific subtypes in the results our sampling efforts have not yet been identified.

Affected fish often show lethargy, an impaired swimming performance, faecal casts, loss of appetite and increased mortality. Fish will tend to congregate at the surface in the cage corners, unable to maintain a normal position. Histopathological findings may include total or severe degeneration of exocrine pancreas and always various degrees of myopathy of skeletal and heart muscle.

Salmon Alphavirus (SAV) in BC was first reported in June 2012 with Department of Wild salmon samples, identified by positive PCR. However, Dr. Michael Kent, wrote of the disease it causes, Pancreas Disease, in Atlantic farm salmon being raised in BC in 1987. Dr. Gary Marty also identified differentials (symptoms) of SAV going back to 2007 in his reports to salmon farming companies in British Columbia (Cohen Commission exhibits).

Transmission: Disease outbreaks have only been observed in sea water and usually 5 to 7 mo after the smolts have been transferred to the sea. SAV is highly durable, and can withstand more than two months in sterile sea water at low temperatures. This durability implies horizontal transmission between adjacent farms, which can occur directly or indirectly. A reservoir in the marine environment can therefore build up and be present long after an outbreak occurs. Possible occurrences of vertical transmission have not been confirmed.

Sea lice may also act as vectors of infection of SAV.

Symptoms and pathology: Affected fish may exhibit such symptoms as damaged pancreas, haemorrhaging and severe cardiac and skeletal myopathies.

Diagnosis: Alphavirus spp. have 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).

Prevention: Improved management conditions on farms, like fallowing, segregation of generations of fish, restrictions on movement of fish and improved surveillance and vaccination on farms can prevent the spread of SAV and subsequent infections of PD or SD.

References:

1. McLoughlin MF, Graham, DA. 2007. Alphavirus infections in salmonids – a review. J Fish Dis 30 (9): 511-531.

2. Crane, M and Hyatt, A. 2011. Viruses of Fish: An Overview of Significant Pathogens. Viruses 3: 2025-2046.

3. Hodneland, K, Bratland, A, Christie, KE, Endresen, C and Nylun A. 2005. new subtype of salmonid alphabrisu (SAV), Togaviridae, from atlantic salmon Salmo sailor and rainbow trout Oncorhynchus mykiss in Norway. Dis Aquat Org 66: 113-120.

4. Nylund A, Plarre H, Hodneland K, Devold M, Aspehaug V, Aarseth M, Koren C, Watanabe K (2003) Haemorrhagic smolt syndrome (HSS) in Norway: pathology and associated virus-like particles. Dis Aquat Org 54:15–2.7

5. Graham, DA, Staples, C, Wilson CI, Jewhurst, HL, Cherry, K, Gordon AW and Rowley HM. 2007. Biophysical properties of salmonid alphaviruses (SAV) influence of temperature and pH on virus survival. J Fish Dis 30: 533-544.

6. Rimstad, E. 2011. Examples of emerging virus diseases in salmonid aquaculture. Aquaculture Research 42: 86-89.

7. Bratland, A and Nylund, A. 2009. Studies on the possibility of vertical transmission in Norwegian Salmonid Alpha Virus in production of Atlantic salmon in Norway. J Aquat Animal Health 21: 173-178.

8. Kent M.L. & Elston R.A. (1987) Pancreas disease in pen-reared Atlantic salmon in North America. Bulletin of the European Association of Fish Pathologists 7, 29–31.