Infectious Salmon Anemia (ISA)

Physical Signs:

• Pale gills: This is indicative of severe anemia and one of the earliest signs of ISA 1.
• Swollen and darkened organs: The liver may appear darkened, and there may be accumulation of fluid in the body cavity (ascites) 12.
• Hemorrhages: Internal bleeding in organs, including blood spots in the eyes 12.
• Exophthalmia: Bulging eyes are often observed in affected fish 2.

Behavioral Changes:

• Lethargy: Infected fish exhibit reduced activity levels 2.
• Loss of Appetite: Decreased feeding behavior and significant weight loss 1.

Causative Agent: Infectious Salmon Anemia Virus (ISAV), a member of the genus Isavirus in the family Orthomyxoviridae 1.

Transmission Methods:

• Direct Contact: Spread between infected and healthy fish 2.
• Waterborne: The virus can spread through water 2.
• Other vectors: Discharge of untreated blood and contact with infected vehicles and equipment 2.

Environmental Factors: While most cases occur in seawater, ISA has occasionally been reported in freshwater farms, particularly those using part seawater 2.

Farm Management Practices: Movement of live fish is considered one of the highest risk factors for disease spread 2.

Clinical Examination: Observation of physical and behavioral symptoms, especially if the hematocrit is less than 10% 1.

Laboratory Tests:

• PCR: RT-PCR is used to detect viral nucleic acids 1.
• Virus Isolation: ISAV can be isolated in specific cell lines like SHK-1, ASK, CHSE-214, or TO cells 1.
• Immunofluorescence: Used to confirm the identity of isolated viruses 1.
• Droplet Digital PCR: A newer method for quantifying ISAV in seawater samples 3.

Vaccines are currently available from pharmaceutical suppliers to the industry. ^[1]
Preventive Measures

Biosecurity Protocols:

• Strict movement controls on suspect farms 2.
• Placing farms in the vicinity of an outbreak under surveillance 2.

Farm Management Practices:

• Compulsory slaughter and disinfection of infected farms 2.
• Regular monitoring of seawater for early detection of viral shedding 3.

Notable Outbreaks:

• Norway (1984): The first identified outbreak, with continuing problems despite control measures 1.
• Scotland (1998-1999): An epizootic that cost an estimated $32 million (U.S.) to eradicate 1.
• Chile (2007-2009): Severe outbreaks that devastated the salmon industry 1.

Response Strategies and Outcomes:

• Scotland (1998-99): The outbreak was successfully eradicated 2.
• Norway: Cases of ISA continue to occur, with 1 to 20 outbreaks annually, mostly clustering in northern Norway in recent years 3.

Lessons Learned: The importance of early detection, with research showing that large viral shedding events occur before fish mortality, providing an opportunity for early intervention 3

ISA Incidence in Canada:

• ISA has been a recurring problem in Canada, particularly in the Bay of Fundy in New Brunswick 1.
• First outbreak was recorded in 1998, which resulted in a $10M CAD support package 11

Geographical Spread:

• The disease has been reported in various regions, including New Brunswick and Nova Scotia 1 10.

Economic Impact:

• ISA results in annual losses of approximately $4.8–$5.5 million (U.S.) to farmers in New Brunswick 1.
• The disease has led to significant economic losses due to the culling of infected fish and fallowing of affected sites 1.

Treatment & Management:

• Canada has implemented biosecurity measures to control ISA, including culling and fallowing affected sites 1.
• Governmental protocols can be found here 12

ISA Incidence in Chile:

• ISA was first reported in Chile in 1996, and outbreaks have continued to occur 1.

Geographical Spread:

• The disease has been reported in various regions, including Los Lagos and Aysén 1.

Economic Impact:

• ISA has caused significant economic losses in Chile, with millions of fish culled in control efforts 1.
• The disease has had a devastating impact on the salmon industry, particularly in the early 2000s 1.
• The Chilean ISA crisis in the mid-2000s is regarded as one of the most economically damaging aquaculture disease outbreaks in history. Salmon production was literally cut in half from about 497,000 metric tons in 2006 down to ~247,000 tons in 2010 it. A Chilean industry analysis estimated the total economic cost of the ISA disaster at around $550–600 million USD 14 15

Treatment & Management:

• Chile has implemented biosecurity measures similar to those in Norway and Scotland, including culling and fallowing affected sites 1.

ISA Incidence in Faroe Islands:

• ISA was first reported in the Faroe Islands in 2000, causing significant losses 1.

Geographical Spread:

• The disease has been reported in various regions of the Faroe Islands 1.

Economic Impact:

• ISA devastated the salmon industry in the Faroe Islands in 2000 1 13.

Treatment & Management:

• The Faroe Islands have implemented biosecurity measures similar to those in other affected countries, including culling and fallowing affected sites 1.

ISA Incidence in Norway:

• Infectious Salmon Anemia (ISA) was first recorded in Norway in 1984 and has since been a recurring challenge in marine farmed Atlantic salmon 69.
• A significant number of ISA cases were reported in Norway during the summer of 2023, affecting multiple farms 8.
• The disease was a serious problem in the late 80s and early 90s, with at least 80 new outbreaks in 1990 at the peak of the epidemic 69.

Geographical Spread:

• ISA outbreaks have been reported in various regions, including Åfjord municipality in Trøndelag county and Volda municipality in Møre og Romsdal county 8.
• Six separate farming zones are currently being monitored for or cleansed of ISA 8.

Economic Impact:

• ISA outbreaks can be costly to Norwegian aquaculture companies due to the need to purge and fallow impacted sites and establish protection and monitoring zones 8.
• The disease has had severe implications for production economics, with high rates of mortality and management restrictions limiting production 6.

Treatment & Management:

• Norway has implemented various biosecurity measures since the early 90s to control the horizontal spread of ISA 6.
• In 2022, updated regulations for handling ISA outbreaks were implemented, including an eradication program to limit outbreaks to fewer than 1% of active locations 8.
• Control measures include stamping out infected populations and setting up protection zones to prevent marine traffic from entering affected areas 8.

ISA Incidence in Scotland:

• ISA was first detected in Scotland in 1998, leading to significant economic losses 1.
• The disease re-emerged in 2009 after being absent for several years 1.

Geographical Spread:

• The disease has been reported in various regions, including the Western Isles and Shetland 1.

Economic Impact:

• An epizootic in Scotland in 1998-1999 cost an estimated $32 million (U.S.) to eradicate 1.
• Recurring outbreaks have continued to impact the industry economically 1.

*Treatment & Management:

• Scotland has implemented strict biosecurity measures to control ISA, including culling infected fish and fallowing affected sites 1.