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Epidemiology::Infectious salmon anemia virus

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Salmon::virus    Disease::anemia    Infected::atlantic    Outbreak::european    North::species    Chile::norway

Epidemiology

Prevalence

In the autumn of 1984, a new disease was observed in Atlantic salmon being farmed along the southwest coast of Norway. The disease, which was named Infectious salmon anemia, spread slowly, but caused the death of up to 80% of salmon stock in some hatcheries.<ref>Collins Edexcel International GCSE Biology, Student Book (ISBN-13 978 0 00 745000 8) p.328</ref> By June 1988 it had become sufficiently widespread and serious to require the Norwegian Ministry of Agriculture, Fisheries and Food to declare it a notifiable disease.

In the summer of 1996, a new disease appeared in Atlantic salmon being farmed in New Brunswick, Canada. The death rate of the fish on affected farms was very high and, following extensive scientific examination of the victims, the disease was named "hemorrhagic kidney syndrome." Although the source and distribution of this disease was not known, the results of studies by Norwegian and Canadian scientists showed conclusively that the same virus was responsible for both infectious salmon anemia and hemorrhagic kidney syndrome.

In May 1998, a salmon farm at Loch Nevis on the west coast of Scotland reported its suspicions of an outbreak of infectious salmon anemia. The suspicions were confirmed, and by the end of the year, the disease had spread to an additional fifteen farms not only on the Scottish mainland but also on Skye and Shetland.

More recently (2008) there has been another outbreak of ISA in Shetland.<ref>http://www.fis.com/fis/worldnews/worldnews.aspfil=e&ndb=1&id=31184 Fish Information and Services</ref> ISA was detected in fish from just one site, which has since been harvested and will remain fallow. There is no evidence the disease has spread beyond this site, but two nearby SSF cages are under suspicion of carrying the disease and are also now clear of fish.

In 2011, two wild Pacific salmon taken from the central coast of British Columbia were suspected to have ISA after preliminary tests showed possible evidence of the virus. However, extensive testing by the Canadian Food Inspection Agency to try and amplify and culture the virus were unsuccessful, prompting the agency to conclude that the ISA virus was not present.<ref>http://www.inspection.gc.ca/english/corpaffr/newcom/2011/20111109e.shtml Canadian Food Inspection Agency</ref> In February 2012, a confirmed outbreak of ISA in Nova Scotia resulted in the destruction of up to 750,000 salmon.{{ safesubst:#invoke:Unsubst||date=__DATE__ |$B= {{#invoke:Category handler|main}}{{#invoke:Category handler|main}}[citation needed] }} In July 2012, a confirmed outbreak of infectious salmon anemia in Newfoundland and Labrador, Canada, prompted the destruction of 450,000 farmed salmon by the Canadian Food Inspection Agency<ref>{{#invoke:citation/CS1|citation |CitationClass=news }}</ref> and an outbreak was also confirmed at another site in late 2012.{{ safesubst:#invoke:Unsubst||date=__DATE__ |$B= {{#invoke:Category handler|main}}{{#invoke:Category handler|main}}[citation needed] }} In mid-2012, another outbreak was identified in Nova Scotia, with the 240,000 fish being allowed by CFIA to mature to market size before being harvested in early 2013 by the operator and processed for the consumer market. After being held by the CFIA, the fish was declared fit for human consumption despite the presence of the virus as the disease "poses no risk to human health".<ref>{{#invoke:citation/CS1|citation |CitationClass=news }}</ref>

In Chile, ISA was first isolated from a salmon farm in the 1990s and described for the first time in 2001<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> although the initial presence never resulted in widespread problems. However, since June 2007, the national industry has been dealing with a serious ISA outbreak which has not yet been completely brought under control and has been responsible for an important decline in the industry, closure of many farms and high unemployment. The virus was detected in an Atlantic salmon farm in Chiloé Archipelago in Los Lagos Region and spread to the fjords and channels of Aysén Region to the south almost immediately<ref>Analizan posible presencia de variante de virus ISA</ref><ref>First detection, isolation and molecular characterization of ISA-v in farmed Atlantic salmon (Salmo salar) in Chile</ref>

Transmission

Transmission of the virus has been demonstrated to occur by contact with infected fish or their secretions. Contact with equipment or people who have handled infected fish also transmits the virus. The virus can survive in seawater and a major risk factor for any uninfected farm is its proximity to an already infected farm.

The Lepeophtheirus salmonis sea louse, a small crustacean parasite that attacks the protective mucus, scales and skin of the salmon has been shown to carry the virus passively on its surface and in its digestive tract. Under laboratory conditions Lepeophtheirus salmonis has been demonstrated to passively transfer ISA.<ref>OIE ISA fact sheet</ref> It is not known whether the Infectious salmon anemia virus can reproduce itself in the sea louse, although this is a possibility as viruses often depend on secondary vectors for transmission like the Arboviruses such as dengue fever, West Nile virus, or African swine fever virus.


Infectious salmon anemia virus sections
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Epidemiology
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