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Infectious Salmon Anemia

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Infectious Salmon Anemia, Canada , November, 1999
Impact Worksheet Update

Summary of previous impact worksheet (issued 06/99):

Infectious salmon anemia (ISA) is a disease of Atlantic salmon caused by an orthomyxovirus. Since its first isolation in Norway in 1984, it has also been found in New Brunswick, Canada in 1996, Nova Scotia in 1998, and in Scotland in 1998. ISA may also be called hemorrhagic kidney syndrome (HKS) in Atlantic salmon. Currently (06/99), the eastern most Maine salmon pen sites are within a 3 mile radius of one of the most recently infected Canadian pens. Because of the significant impact ISA has on production and the unknown benefits from vaccination, the impact to the local Maine economy from decreased production could be significant. Economic impact outside of the local area in Maine is likely to be minimal. There is need for further data collection and analysis to address such issues as vaccine efficacy and risk factors for disease transmission.



Prepared by: Center for Emerging Issues, Centers for Epidemiology and Animal Health
Animal and Plant Health Inspection Service, USDA


Current situation

On October 27, 1999, Canada reported to the OIE that infectious salmon anemia (ISA) virus was detected in 4 Atlantic salmon (Salmo salar) aquaculture escapees and 10 adult wild Atlantic salmon returning to the Magaguadavic river, New Brunswick, Canada. The Magaguadavic river runs parallel to and approximately 10 - 20 miles east of Maine’s Canadian border. In addition, it was announced in early November, 1999 by Mr. John Home Robertson, Scottish Fisheries Minister, that the ISA virus had been found in wild fish in Scotland.

Although ISA has been present in Canadian aquaculture pens since 1996, this is the first time the virus has been found in wild salmon outside an aquaculture cage. Identification of the virus was made by virus isolation and culture. Typically, the wild salmon are caught in a trap on the river, and separated from escaped cultured fish using scale conformation and fin appearance. The wild salmon are transported to a culture facility to be held in tanks until ready to spawn. Two of the wild caught infected salmon were held up to 6 weeks in these tanks, which are supplied by brackish well water, before being diagnosed with ISA. One was severely affected by sea lice. It is unclear how long the other 8 wild salmon were held prior to testing for ISA. (personal communication, Dr. Steve Ellis; OIE Disease Report)

It is unknown exactly how the wild salmon became infected with ISA. There are many possibilities, some of which include the following: exposure to ISA infected wild or farmed salmon while in the ocean, exposure to infected escaped cultured fish at the fish trap, or exposure at the holding facility to other infected fish or waterborne pathogens in the holding tank.

Canada’s response

The Canadian Federal Department of Fisheries and Oceans (DFO) is continuing to collect and analyze wild marine fish (over 200 samples are now being tested) for presence of ISA virus, as well as additional wild and cultured salmon when they become available. DFO will be testing an additional 100 broodstock salmon from the Saint John and Saint Croix rivers in the next few weeks.

An autogenous vaccine for ISA used in New Brunswick, Canada in 1999 smolts has an unknown level of efficacy. Out of 84 pen sites in New Brunswick, 18 were found to be clinically positive for ISA and 2 more had virus isolation but no clinical disease. Of the 18 clinically positive sites, 8 contained vaccinated fish. The entire class of 1999 smolts were vaccinated, however, sites are made up of multiple year class (ages) of salmon. So unless a pen site had 100% 1999 smolts, it would have had some combination of vaccinated and unvaccinated fish. In addition, some pens would have had no vaccinated fish. (personal communication, Steve Ellis). Because there were no clinical trials of this vaccine (not required by law since this is an autogenous vaccine), it is difficult to determine exactly why the vaccine efficacy appears low. The lack of immunity in these vaccinated salmon could be due to the vaccine itself, immunologic interference due to the vaccine being given along with other vaccines, or that immunity was not established before the smolts were placed in the pen sites and exposed. Another vaccine for ISA is now being produced by a second Canadian company.

U.S. activities affecting wild and farmed salmon

A biological report jointly released by the US Fish and Wildlife Service and the National Marine Fisheries Service on October 8, 1999 concludes that Atlantic salmon is in danger of extinction. The proposed Endangered Species Act protection areas include all coastal watersheds with native populations of Atlantic salmon north of and including tributaries of the lower Kennebec River (below Edwards Dam) to the mouth of the St. Croix River at the US-Canadian border. There are at least eight rivers in the area with wild salmon populations, including the Dennys, East Machias, Machias, Pleasant, Narraguagus, Ducktrap, and Sheepscot Rivers and Cove Brook. In addition, Canada’s Atlantic Salmon Federation is urging their Minister of Environment to place the inner Bay of Fundy strains of Atlantic salmon on the national strategic priority list for endangered species under Canada's new Species at Risk Act (SARA). Experiments have indicated that the virus does not pass from parent to egg, therefore spawning the broodstock from the currently infected salmon in order to maintain the genetic line of the river is being considered.

The US Fish and Wildlife Service has been involved with surveillance for ISA in the wild salmon populations in Maine. Wild salmon are caught in rivers and placed in their hatchery for 3 to 4 years until they are ready for spawning. Any salmon which die at the time of capture or at any time while in the holding facility are tested for disease pathogens, including ISA virus. Approximately 30 fish are tested from vent swabs each year from that year’s newly caught fish. In addition, 400-500 spawning adults are tested using reproductive fluid samples each year. To date, no wild salmon caught in US waters have been found positive for ISA virus. The salmon aquaculture community in Maine continued surveillance for ISA in 1999 with no clinical ISA or virus found.

Please contact Victoria Bridges (970) 490-7822 or Katherine Marshall (970) 490-7801 with any questions or comments.

Prepared by: Center for Emerging Issues, Centers for Epidemiology and Animal Health

Animal and Plant Health Inspection Service, USDA

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