Salmon Pancreas disease (PD or SPD) is caused by a species of Salmonid ''

Alphavirus ''Alphavirus'' is a genus of RNA viruses, the sole genus in the ''Togaviridae'' family. Alphaviruses belong to group IV of the Baltimore classification of viruses, with a positive-sense, single-stranded RNA genome. There are 32 alphaviruses, ...

'' (SAV) called ''Salmon pancreas disease virus'' (SPDV). The virus was first described in 1976 in Scotland and in 1989 in Norway. It affects farmed

Atlantic salmon The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlantic salmon are ...

(''Salmo salar'') caused by Marine SAV2 and SAV3 and has also been identified in

Rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...

(''Oncorhyncus mykiss'') in the seawater phase caused by SAV2 where the disease is commonly referred to as Sleeping Disease (SD).

Salmonid Alphavirus

Salmonid Alphavirus is an

RNA virus An RNA virus is a virusother than a retrovirusthat has ribonucleic acid (RNA) as its genetic material. The nucleic acid is usually single-stranded RNA ( ssRNA) but it may be double-stranded (dsRNA). Notable human diseases caused by RNA viruses ...

. Six genotypes of SAV have been identified (referred to as SAV1, 2, 3, 4, 5 and 6), differentiated by the

nucleic acid sequence A nucleic acid sequence is a succession of Nucleobase, bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequence ...

s of certain genes. The strains of SAV causing PD belong to the genotypes SAV1, Marine SAV2 and SAV3.

Diagnosis

When the fish is infected, it can cause sudden

loss of appetite Anorexia is a medical term for a loss of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others i ...

lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...

and increased

mortality Mortality is the state of being mortal, or susceptible to death; the opposite of immortality. Mortality may also refer to: * Fish mortality, a parameter used in fisheries population dynamics to account for the loss of fish in a fish stock throug ...

. The general symptoms of this virus infection also include difficulties to maintain a correct position in the water due to muscle damage.

Transmission

Cross infection is caused by seawater currents, human activities and lacking measures to prevent risk of transmission between sites.

Fallowing Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...

procedures have proved successful and prevents the survival of the virus in the environment through the fallowing period, and repeated disease outbreak on the same site is due to introduction of new virus.

Geographical distribution

Most research is performed in Ireland, Scotland and Norway but the virus has also been identified in England and Mainland Europe where the SAV2 virus affects rainbow trout.

Economic impact

The virus is highly infectious and causes large economic losses in the fish farming industry, particularly in Norway and Scotland. In 2010, the economic loss was estimated to be 0.72 € per kg in Norwegian salmon production due to high mortality rates, reduced growth and the quality of the finished product.

Prevention and treatment

A monovalent vaccine against PD was made commercially available in 2007 and a multivalent vaccine, capable of immunising the fish against multiple strains of the SPDV, was introduced in 2015. Vaccination is shown to reduce the risk of the fish being infected and reduces the mortality rates due to PD. In addition, vaccination reduces

viral shedding Viral shedding is the expulsion and release of virus progeny following successful reproduction during a host (biology), host cell (biology), cell infection. Once replication has been completed and the host cell is exhausted of all resources in ma ...

into the environment (virus being released from the cells) from already infected individuals, reducing the risk of contamination of neighbouring

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s. Commercially available fish feed has also been used in an attempt to improve the fish's immune system, but the efficiency of this has not been documented. In Norway, a combination of vaccination, improve

biosecurity Biosecurity refers to measures aimed at preventing the introduction and/or spread of harmful organisms (e.g. viruses, bacteria, etc.) to animals and plants in order to minimize the risk of transmission of infectious disease. In agriculture, thes ...

measures, depopulation, closure of poorly managed fish farms and geographical separation of sites has proved to reduce PD outbreaks. In addition, regularly updated interactive maps are updated daily allowing all interested parties to monitor and contribute to the current state of PD geographically. Between 2009 and 2011 there were between 75 and 89 outbreaks per year. To prevent spreading the Norwegian coastline was in 2008 divided into two administrative zones separated by a production free zone of 10

nautical mile A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as the meridian arc length corresponding to one minute ( of a degree) of latitude. Today ...

s at the same time a vaccination programme was introduced. However, the effect of this has been questioned since the number of PD outbreaks has not been reduced.

References

{{Taxonbar, from=Q18976378 Fish diseases Alphaviruses Animal viral diseases