Infectious salmon anemia
1891639
205623328
2008-04-14T19:57:20Z
Eugene van der Pijll
22016
Reverted edits by [[Special:Contributions/121.217.243.211|121.217.243.211]] ([[User talk:121.217.243.211|talk]]) to last version by Anticipation of a New Lover's Arrival, The
{{refimprove|date=September 2007}}
{{Taxobox
| name = Orthomyxoviridae
| virus_group = v
| familia = '''''Orthomyxoviridae'''''
| subdivision_ranks = Genera
| subdivision = ''[[Influenzavirus A]]''<br>
''[[Influenzavirus B]]''<br>
''[[Influenzavirus C]]''<br>
''[[Isavirus]]''<br>
''[[Thogotovirus]]
}}
'''Infectious salmon anemia''' or '''anaemia''' ('''ISA''') is a [[virus|viral]] [[disease]] of [[Atlantic Salmon]] (''Salmo salar'') that affects [[aquaculture|fish farms]] in [[Canada]], [[Norway]], [[Scotland]] and [[Chile]], causing severe losses to infected farms.
The [[aetiological]] agent of ISA is the infectious salmon anaemia virus (ISAV). ISAV, a RNA virus, is the only species in the genus "Isavirus" which is in the family [[Orthomyxoviridae]].
==Pathology==
As the name implies, it causes severe [[anemia]] of infected [[fish]]. Unlike mammals, the red blood cells of fish have DNA, and can become infected with viruses. The fish develop pale [[gill]]s, and may swim close to the water surface, gulping for air. However, the disease can also develop without the fish showing any external signs of illness, the fish maintain a normal appetite, and then they suddenly die. The disease can progress slowly throughout an infected farm and, in the worst cases, death rates may approach 100%. [[Post-mortem]] examination of the fish has shown a wide range of causes of death. The [[liver]] and [[spleen]] may be swollen, congested or partially already dead. The [[circulatory system]] may stop working, and the blood may be contaminated with dead [[blood cell]]s. [[Red blood cells]] still present often burst easily and the numbers of immature and damaged blood cells are increased.
Infectious salmon anemia appears to be most like [[influenza]] viruses. Its mode of transfer and the natural reservoirs of infectious salmon anemia virus are not fully understood. Apart from Atlantic salmon, both sea-run [[Brown trout]] (''Salmo trutta'') and [[Rainbow trout]] (''Onchorhyncus mykiss'') can be infected, but do not become sick, so it is thought possible that these species may act as important [[asymptomatic carrier|carriers]] and reservoirs of the virus.
==Spread of the disease==
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. By June [[1988]] it had become sufficiently widespread and serious to require the [[Government of Norway|Norwegian Ministry of Agriculture, Fisheries and Food]] to declare it a [[List of notifiable diseases|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 [[Isle of Skye|Skye]] and [[Shetland]].
==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, not surprisingly, a major risk factor for any uninfected farm is its proximity to an already infected farm.
More recently the [[sea louse]], a small [[crustacean]] [[parasite]] that attacks the protective [[mucous]], [[scale (zoology)|scales]] and [[skin]] of the salmon has been shown to carry the virus passively on its surface and in its digestive tract, although transmission of the disease by sea lice has not been demonstrated. It is not known whether the Infectious salmon anemia virus can reproduce itself in the sea louse, although this is a remote possibility as [[viruses]] are usually very host specific unlike [[bacterial]] diseases that can replicate in [[ticks]] such as [[Lyme disease]] and [[Rocky Mountain Spotted Fever]].
==Control and treatment==
ISA is major threat to the viability of salmon farming and is now the first of the diseases classified on List One of the [[European Commission]]’s fish health regime. Amongst other measures, this requires the total eradication of the entire [[fish stocks|fish stock]] should an outbreak of the disease be confirmed on any farm. The economic and social consequences of both the disease and the measures used to control it are thus very far reaching.
Infectious salmon anemia is currently regarded as a serious threat not only to farmed salmon, but also to dwindling stocks of wild salmon. Anecdotal evidence suggests that fish which survive the first infection become immune to the virus. Work is now underway to develop a [[vaccine]] against ISA. A recent report suggests that the North American virus may be slightly different from the Norwegian virus. This makes it unlikely that the sudden appearance of the disease, at least in Canada, was due to the importation of infected Norwegian fish. The possibility then is that a single vaccine might only be effective in a limited area and maybe only for a limited time.
==References==
*Ely, B. [http://www.nimr.mrc.ac.uk/MillHillEssays/1999/isa.htm Infectious Salmon Anaemia]. Mill Hill Essays, National Institute for Medical Research.
*Raynard RS, Murray AG, Gregory A (2001) Infectious salmon anaemia virus in wild fish from Scotland, Diseases of Aquatic Organisms, Vol. 46: 93-100
[[Category:Fish diseases]]
[[Category:Animal virology]]
[[Category:Orthomyxoviridae]]
[[de:Ansteckende Blutarmut der Lachse]]