Infectious salmon anaemia

Infectious salmon anaemia (ISA) is an infectious viral disease of Atlantic salmon (Salmo salar L.). The disease was first reported in Norway in 1984, but has since been reported in Canada, the USA, the Faroe Islands, Ireland and Scotland. The outbreak of ISA in Scotland in 1998-99 was successfully eradicated. Atlantic salmon is the only susceptible species known to develop clinical disease, but ISA virus can replicate in rainbow trout (Oncorhynchus mykiss) and sea trout (Salmo trutta L.).

Infectious Salmon Anaemia (ISA)

What is it?

Where and When Might it Occur?

Infectious salmon anaemia (ISA) is an infectious viral disease of Atlantic salmon (Salmo salar L.). The disease was first reported in Norway in 1984, but has since been reported in Canada, the USA, the Faroe Islands, Ireland and Scotland. The outbreak of ISA in Scotland in 1998-99 was successfully eradicated. Atlantic salmon is the only susceptible species known to develop clinical disease, but ISA virus can replicate in rainbow trout (Oncorhynchus mykiss) and sea trout (Salmo trutta L.).

The causative agent of ISA is an orthomyxovirus. The presence of the virus is confirmed by isolation and identification techniques, indirect fluorescent antibody test (IFAT) and reverse transcriptase polymerase chain reaction (RT-PCR).

Diagnosis

The virus can be transmitted through water, but the highest risk factors for spread of disease are movement of live fish, discharge of untreated blood and contact with infected vehicles and equipment

Control

ISA is exotic to the European Union. It is a notifiable disease under UK legislation and a List I disease under European Directive 91/67/EEC. Under EU legislation action must be taken to contain any outbreak, to eradicate sources of infection and to protect other fish farms by:

• Compulsory slaughter and disinfection of infected farms

• Strict movement controls on suspect farms

• Placing farms in the vicinity of an outbreak under surveillance

There are no treatments for ISA and no licensed vaccines in the EU. Vaccine trials in Canada have yielded equivocal results.

Cases of clinical disease may be characterised by severe anaemia, ascites (accumulation of fluid in the body cavity), haemorrhage in internal organs and darkening of the liver.

For more information on ISA view the Fisheries Research Services poster here

Image: Marine Scotland