Infectious salmon anaemia

Infectious salmon anaemia (ISA) is a virus-induced disease that primarily affects farmed Atlantic salmon. There are two variants of ISA virus, i.e. a pathogenic and a non-pathogenic form.

The disease primarily affects farmed Atlantic salmon. However, ISA virus has been detected in other asymptomatic carrier species, such as brown trout. The non-pathogenic form of the virus has been identified in wild Atlantic salmon.

The pathogenic form of ISA virus may cause one or more symptoms in infected salmon, such as:

• pale gills
• swelling of the abdomen
• bleeding in the eyes and skin
• slow swimming and surface air intake.

The disease can lead to the death of diseased fish.

It can be confused with viral hemorrhagic septicemia.

The infectious salmon anaemia virus is found in skin mucus, feces, urine and blood. It is transmitted through contact with infected fish or water contaminated with the virus. The routes of entry for the virus are the gills, skin lesions, eyes and the digestive system. Although transmission from females to eggs has not been demonstrated, it cannot be excluded. Infected fish can release viral particles several weeks before symptoms appear.

Equipment or boats from sites contaminated with the virus also contribute to its transmission. Sea lice, a common parasite of farmed salmon, are also capable of transmitting the disease.

Infectious salmon anaemia outbreaks occur in the spring and late fall when the water temperature is between 3°C and 15°C.

Risk for wildlife health

Wild Atlantic salmon are susceptible to the virus. Only its non-pathogenic form has been detected in wild salmon without symptoms of the disease. The impact of infectious salmon anaemia on wild salmon populations is still poorly understood.

Risk for domestic animal health

Depending on the strain of the virus, up to 90% of farmed salmon can succumb to the disease during outbreaks, but the average mortality rate is 30%. The disease causes significant economic losses in several countries where there is Atlantic salmon farming.

In farming operations, producers can manage the disease through various measures, such as:

• conducting regular monitoring of ponds or cages;
• leaving a period of fallowing between production cycles;
• cleaning and disinfecting pools, cages and equipment used;
• using quarantine measures;
• quickly disposing of infected fish.

In farming, the removal of infected salmon from infected tanks, cages or farms is the procedure used to limit the spread of the virus.

Risk for human health

The disease does not pose any risk for human health. Adopting some safe practices when preparing and cooking wild fish still remains relevant.

In Canada, ISA has been detected on farms in New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland. In Québec, it is suspected that the non-pathogenic form of the virus is present in wild Atlantic salmon.

Infectious salmon anaemia is a reportable disease for Canada. Any person who suspects or detects the presence of ISA in domestic or farm animals is required by law to notify the Canadian Food Inspection Agency .

Veterinarians and laboratory managers must also report the disease to the ministère de l'Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs and the ministère de l'Agriculture, des Pêcheries et de l'Alimentation. Fish producers must report this disease to their veterinary doctor.

Fish from the natural environment that exhibit the characteristic lesions of ISA should be reported.