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Facts about infectious salmon anaemia (ISA)

What we know about the disease

  • outbreaks occur when water temperatures are between 3°C and 15°C
  • an outbreak of ISA does not affect all the finfish in the facility at the same time
  • removal of the affected finfish from the facility stops or substantially slows down the progression of the outbreak
  • the ISA virus does not survive for long in natural seawater, only for a few hours
  • most Pacific salmon and rainbow trout are resistant to ISA

What we would like to know about the disease

  • which genes of the virus cause disease so that we can predict when a severe outbreak is likely to occur
  • which genes of the virus can be reliably used to trace the spread of the infection or outbreak
  • which genes of the virus cause infection of finfish so that a vaccine against infection can be developed
  • mutation capability of the ISA virus from no or low significance to high significance and what factors increase or decrease the capability
  • how long the ISA virus survives in naturally occurring freshwater
  • susceptibility of pink salmon to infection with ISA virus and development of disease
  • wild finfish reservoirs of the ISA virus for cultured finfish sharing the same habitat

Infectious salmon anaemia (ISA) is a disease affecting finfish and is caused by a virus that belongs to a family of viruses called Orthomyxoviridae.

ISA does not infect humans and is not a risk to food safety.

A study led by the European Union in 2000 concluded that ISA cannot be transmitted to humans from live or dead animals.

ISA is a reportable disease in Canada. If you own or work with finfish and suspect or detect ISA, you must report it to the Canadian Food Inspection Agency (CFIA). Here's how:

Infectious salmon anaemia in Canada

ISA was first detected in farmed Atlantic salmon in New Brunswick in 1996. Since then, the virus has also been detected in farmed Atlantic salmon in Nova Scotia, Prince Edward Island and Newfoundland and Labrador.

ISA has been detected in wild salmon in Quebec but has not occurred in the rest of Canada, including the Pacific Ocean watershed of British Columbia.

Declarations by province and marine areas provides information about where ISA occurs in Canada.

Federally reportable aquatic animal diseases in Canada identifies cases of ISA we have confirmed in Canada.

Species of finfish that can be infected

Species of finfish that can become infected with the ISA virus are:

One genetic strain of rainbow trout has been experimentally infected with ISA. This strain of trout does not occur naturally in Canada and is not farmed. ISA has not been found in wild or farmed rainbow trout in Canada.

Signs of infectious salmon anaemia

Only some strains of the virus cause disease and potentially kill finfish. Most of the virus strains identified in the Atlantic region do not lead to disease and death. One strain in particular does not cause disease. This strain is described as non-pathogenic ISA virus. You may also see this strain described as non-deleted highly polymorphic region (HPR) ISA virus or HPR0.

Not all disease-causing strains of ISA virus (also described as pathogenic ISA virus or HPR-deleted ISA virus) cause fatal disease. Some strains cause no obvious disease or a mild increase in disease. Some strains cause a moderate increase in disease and, less commonly, a few strains cause a severe increase in disease.

ISA outbreaks are most often seen in cultured Atlantic salmon reared in seawater. They also occasionally occur in freshwater hatcheries of Atlantic salmon. The disease tends to be slow moving, so the death rate is initially low and increases over weeks or months.

Affected finfish may exhibit any of the following external signs:

Affected finfish may exhibit any of the following internal signs:

Managing infectious salmon anaemia

No treatment is currently available for this disease, although a vaccine is available in Canada. Talk to your veterinarian about whether this vaccine can be an effective tool to manage this disease on your farm.

The ISA virus can be spread between finfish that come into contact with discharged bodily wastes or mucus secretions from infected finfish. It can also be spread through water contaminated with the virus.

People can also spread the virus to other finfish by moving infected live or dead finfish, by using contaminated equipment, vehicles and boats, or by using or moving contaminated water.

You can prevent the introduction of the ISA virus into your farm and prevent the spread of the virus within your farm by using specific safety practices. You can find out more about what practices you need to consider by visiting Biosecurity for aquatic animals. Talk to your veterinarian about what practices are most effective to manage this disease for your farm.

In areas where ISA is known to occur, you may also need to follow additional practices that are required by your provincial ISA control program.

CFIA's initial response to a notification

When you notify a CFIA veterinary inspector of the possible presence of ISA in your finfish, we will launch an investigation, which could include an inspection of the facility.

We will note all relevant information you can provide, such as species affected, life stages affected, signs of illness in the animals, vaccination history, presence of any other diseases and water temperature.

At the same time, we will collect samples for testing at one of Canada's three National Aquatic Animal Health Laboratories.

We may issue movement controls on the animals and equipment, including vehicles and boats. Movement controls are always issued immediately if the farm is in an area where ISA is not known to occur.

We evaluate all the collected information and test results to confirm the presence of ISA on the farm.

The Agency also confirms the presence of ISA in wild finfish. The Agency receives notifications from provincial or federal staff who have investigated a wild fish death event.

CFIA's response once the disease is confirmed

Further disease response measures will either eradicate ISA from the facility or geographically contain the disease. The response measures are also determined by whether the farm is located in an area where the disease occurs or is not known to occur. Aquatic animal disease investigation and response provides information about CFIA's response. Although each disease investigation and response situation is different, the steps involved are often similar.

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