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[[Category:To Do - CABI]]
Also Known As – '''''ISA'''''
Caused By – ''Infectious Salmon Anaemia Virus – ISAV''
==Introduction==
Infectious Salmon Anaemia is a '''[[Viruses|viral]] disease of fish, caused by an enveloped [[Orthomyxoviridae|orthomyxovirus]]'''. Disease may be severe, systemic and lethal but is also subclinical in some fish species.
This disease is '''not considered zoonotic.'''
==Distribution==
Norway, Canada, Scotland, Eastern USA, Chile and Ireland.
The virus '''replicates within the sea trout''', forming a marine reservoir for the virus, and their migration allows distant distribution of the disease.
Transmission is mainly '''via the water, virus being shed into it in mucus, faeces, urine and also via the skin'''.<ref name="TD"> Thorud, K., Djupvik, H. O (1988) '''Infectious anaemia in Atlantic salmon (Salmo salar L.)'''. Bulletin of the European Association of Fish Pathologists, 8(5):109-111</ref> It then enters vulnerable fish via the '''gills or broken skin'''. ISA also has a crustacean vector for transmission.
Spread between netpens is usually slow, and mortality and severity often varies between them.
==Signalment==
A range of salmonid fish can be affected including rainbow trout, sea trout, Atlantic cod, chum, coho, Chinook and atlantic salmon and arctic charr. Both wild and farmed fish are susceptible.
==Clinical Signs==
Disease results in '''severe anaemia and multi-organ haemorrhage. This may be''' seen as '''pallor, abdominal distension, scale oedema or fluid accumulation''' in the abdomen and musculature. The '''gills often pale''' first and most markedly. Fish may develop a “pop-eye” appearance '''(exopthalmos)''', be lethargic and '''sink''' to the bottom of their habitat.
'''Haematocrit values below 10''' are seen in advanced disease, commonly being found <25 and thus leading to multi-organ dysfunction.
Mortality usually varies between affected farms and between netpens on a farm, but can reach 90%.
==Diagnosis==
'''Clinical signs and pathological/histopathological findings''' are highly suggestive of ISA. '''Hepatomegaly, ascites and splenomegaly''' are marked with white/grey patches of necrosis often visible on the liver and dark red splenic congestion. '''Petechiation in the adipose tissue and swim bladder''' is also common.<ref name="TD" /> The major histopathological feature is'''multifocal haemorrhagic necrosis of the liver''' that may become confluent.<ref> Evensen, O., Thorud, K. E., Olsen, Y. A (1991) '''A morphological study of the gross and light microscopic lesions of infectious anaemia in Atlantic salmon (Salmo salar)'''. Research in Veterinary Science, 51(2):215-222; 23</ref> This leads to '''congestion and sinusoid dilation which eventually fill with blood'''. The sinusoid endothelium degenerates and eventually disappears entirely. In diseased fish in the USA in particular, '''renal interstitial haemorrhage''' is a dominant feature, with tubular necrosis, congestion and cast formation.
The virus can also now be '''isolated in cell cultures, detected by Indirect Immunofluorescent Antibody Testing (IFAT) in tissue imprints or detected in fixed sections by immunostaining''' for definitive diagnosis. '''PCR''' tests are also available in the form of RT-PCR.
==Treatment==
There is '''no treatment''' for infected fish.
==Control==
As transmission between farms is generally via the movement of fish or their breeding/meat products, implementation of '''general hygiene legislation and movement procedures''' may greatly reduce incidence of ISA. '''Slaughterhouse and transport regulations''' must also be set and followed.
{{Learning
|flashcards = [[Infectious Salmon Anaemia Flashcards]]
}}
==References==
<references/>
Animal Health & Production Compendium, '''Infectious Salmon Anaemia Virus datasheet''', accessed 07/07/2011 @ http://www.cabi.org/ahpc/
Animal Health & Production Compendium, '''Infectious Salmon Anaemia datasheet''', accessed 07/07/2011 @ http://www.cabi.org/ahpc/
[[Category:To Do - CABI review]] [[Category:Lymphoreticular & Haematopoietic Diseases – Fish]]