What is Infectious Salmon Anemia virus (ISAv)?

What is Infectious Salmon Anemia virus (ISAv)?

ISAv is an influenza-like virus (Orthomyxovirus) that can be transmitted vertically, through the eggs of an infected female to her offspring, or horizontally, from fish to fish.  There is also evidence that sea lice may serve as a vector for viral transmission. ISAv is most commonly found in Atlantic salmon, where it can be highly virulent (particularly in the high density rearing conditions found in net pens and hatcheries), but is also found in herring and sea trout (a non-salmonid species in the Atlantic ocean), which may serve as reservoirs of infection, meaning they can pass the virus to other species but may not become diseased themselves.  A study published in 2003 tested the susceptibility of some Pacific salmon species (sockeye salmon were not tested) to two strains of  ISAv; though Pacific salmon were resistant to the initial ISAv exposure, the virus mutates rapidly and the authors concluded that  “the potential for ISAV to adapt to Oncorhynchus spp. should not be ignored” (Rowland and Winton, 2003).  ISAv has been found across much of the North Atlantic and was introduced to Chile via infected Norwegian salmon eggs, where it caused widespread mortalities in farmed Atlantic and coho salmon, indicating that Pacific salmon are at risk.  The importation of Atlantic salmon eggs as a route of viral entry is of great concern in the eastern Pacific.

The first public report of ISAv in the Pacific Northwest was on October 15th, 2011 from juvenile sockeye salmon from the west coast of Vancouver Island, BC.  The samples were analyzed by the laboratory of Dr. Fred Kibenge at the Atlantic Veterinary College, which serves as the World Organization for Animal Health’s ISAv reference laboratory for the western hemisphere, and thus the results are very credible.  Within ten days, the virus was also detected in adult Chinook, coho, and chum salmon from a tributary of the Fraser River, BC.  Attempts to replicate these findings by other laboratories have met with limited success; the original sockeye samples were completely consumed during the initial testing, and further tests on the adult positive samples could not be repeated.  Canada’s federal Department of Fisheries & Oceans (DFO) also tested these samples and recently declared that they were negative, although they pointed out that the samples were in poor condition and may not have been viable, leaving the issue unresolved.  The discovery was referred to as a disease emergency with “global implications” by Dr. James Winton, fish health section chief of the U.S. Geological Survey’s Western Fisheries Research Center.

As of November 29, 2011, it appears as if the virus has been present in BC since at least 2002, and Canada’s DFO failed to report it. A 2004 draft manuscript, leaked out of DFO, indicates that the deadly virus was identified nine years ago in coho, pink and sockeye salmon taken from southern BC, Southeast Alaska and Bering Sea waters.

On December 2, 2011, Federal officials from DFO and the Canadian Food Inspection Agency (CFIA) released a statement: “The Government of Canada in collaboration with the Province of British Columbia has completed testing all samples related to the suspected infectious salmon anaemia investigation in BC. Based on the final results, there are no confirmed cases of the disease in wild or farmed salmon in BC.”

On December 15, 2011, during the reconvened Cohen Commission hearings, Dr. Kristi Miller, head of molecular genetics at the federal Pacific Biological Station in Nanaimo, provided testimony that suggested ISAv has been present in BC salmon as far back as 1986.

ISAv has quickly become a confusing story, especially with all the conflicting reports from federal/local agencies, different conservation groups, and the constant stream of media releases. See ISAv FAQ’s for more info. The fact remains that we need to learn more about ISAv and the potential threat it poses to wild fish.

WFC has moved quickly to raise awareness of the threat and to encourage state and federal agencies to begin sampling immediately and establish a laboratory to analyze ISAv samples.  In contrast to the sluggish response of the BC government, Senators Maria Cantwell (D-WA), Lisa Murkowski (R-AK), and Mark Begich (D-AK), released a statement on November 2nd:

“We urge the U.S. government to obtain samples from the two infected sockeye and run independent diagnostic tests to confirm the presence of the ISA virus in British Columbia.  We should not rely on another government – particularly one that may have a motive to misrepresent its findings– to determine how we assess the risk ISA may pose to American fishery jobs… One recent study of Pacific salmon estimated the wholesale value of the annual catch at least $2.2 billion dollars, supporting 35,000 harvesting and processing jobs…With so much at stake, a rapidly spreading virus that causes disease in wild Pacific salmon could be economically and ecologically devastating…While a few scientists may downplay the threat to wild Pacific salmon posed by the ISA infections recently detected in British Columbia, we believe the lessons learned from other recent fish disease outbreaks suggest that ISA should be cause for considerable concern now.”

Senators Maria Cantwell (D-WA), Lisa Murkowski (R-AK), and Mark Begich (D-AK)

The presence of this virus poses a serious threat to native salmon species that are already in decline or endangered.   WFC staff have already started sampling for ISAv in Washington waters, focusing on the Skagit River because of its proximity to the Fraser River basin.  In addition, we are working with colleagues in British Columbia to create a standard sampling protocol to be used coast-wide and to obtain samples from BC for testing by U.S. facilities.

Infected fish may exhibit lethargy, skin darkening, severe anemia (pale gills), “petechial hemorrhaging” (small blood spots on the abdomen, particularly near the pectoral fins and vent), and abdominal swelling.  Internally, dark livers, swollen spleen tissue, and petechial hemorrhaging in the intestines and abdominal cavity are often associated with ISAv infection.  However, in Pacific salmon, the infection may present itself differently. Reports of “jaundiced” (yellow skin) salmon from BC and the Skagit River may indicate ISAv; this is an area of research here at WFC.

To report infected fish, or if you’d like to help us sample, contact: Jamie Glasgow. Please email us pictures of infected fish!

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