The Alaska Department of Fish and Game says it is closely monitoring and evaluating a recent report that samples taken from sockeye salmon in British Columbia show exposure to Infectious Salmon Anemia Virus (ISAv).
The test results, reported by researchers from Simon Fraser University, are based on a limited sample of sockeye salmon smolts from Rivers Inlet in central B.C. The smolts were not exhibiting any outward signs of infection.
Research on ISAv indicates that the risk to Alaska’s salmon stocks is low, say agency officials.
The say Pacific salmon have been shown to be mostly resistant to ISAv, which is a flu-like disease of Atlantic salmon.
ISAv does not transmit to humans and is not a human health or food safety issue.
“Right now, there is a lot of misinformation out there about this finding and this disease,” said Ted Meyers, ADFG fisheries scientist. “The Rivers Inlet results are being analyzed through additional testing in a second laboratory to rule out any false positives. At this point we are concerned, but do not want to over react as we await more definitive information from Canada.”
Live Atlantic salmon are not allowed to be imported into Alaska. However, if the virus is confirmed present in British Columbia migratory Pacific salmon or the Atlantic salmon stocks prevalent in British Columbia fish farms, there is concern over potential impacts to Alaska salmon stocks.
“The department’s pathology lab is in contact with agencies in Canada and will continue monitoring the situation,” said Cora Campbell, commissioner, Alaska Department of Fish and Game. “We will take all necessary measures to protect our stocks.”
Additional information on ISAv and the reports from B.C. can be found on the ADF&G web site at http://www.adfg.alaska.gov/index.cfm?adfg=pressreleases.isav_info
Recently, two of 48 wild sockeye salmon smolts were test-positive by polymerase chain reaction (PCR) for a European strain of ISAv from River’s Inlet, British Columbia.
The test was conducted by the Prince Edward Island Veterinary College, which is the ISAv reference laboratory for Canada. These smolts were reportedly normal in appearance and behavior. Some strains of ISAv will not grow in cell culture and, therefore, must be detected by molecular methods such as PCR. The PCR test detects the nucleic acid of the virus but does not indicate whether the virus is viable and infectious.
Although the test has a high specificity of detection, false positives are possible.
ISAv is an enveloped single stranded RNA orthomyxovirus belonging to the influenza virus group. The virus has caused disease and severe losses in Atlantic salmon and was first detected in Norway in 1984. Subsequently, 12 years later the virus caused devastating losses of Atlantic salmon in various locations including the Maritime coast of North America (New Brunswick and Maine in 1996 and 2001, respectively) and Chile in 2007.
ADFG highlighted the following considerations regarding the B.C. ISAv report results:
-- The River’s Inlet PCR results must be confirmed by additional testing in a second laboratory to rule out any false positives. A positive PCR by itself is not sufficient by OIE standards to confirm whether the virus or the disease is present in B.C.
-- If these results are confirmed, there would be concern over potential impacts to Alaska salmon stocks.
-- ISAv does not transmit to humans and is not a human health or food safety issue.
-- Research on ISAv indicates that risk to Alaska’s salmon stocks is low. Pacific salmon are relatively resistant to infection and disease from ISAv, which is a viral disease of Atlantic salmon. The susceptibility of sockeye salmon to ISAv has not been experimentally tested. Other Pacific salmon including chinook, coho, and chum as well as steelhead trout do not develop disease when injected with the Norwegian strain of ISAv, but may become infected and carry the virus for varying periods of time. However, injection is an unnatural route of infection that would not occur in nature.
-- Other strains of ISAv in North America are not pathogenic in Atlantic salmon. However, these viruses can mutate into more virulent strains, therefore we have reason for concern.
-- Atlantic herring reportedly carry the virus, but do not become diseased. This forage species could act as a reservoir and source of the virus.
Although Atlantic salmon are prohibited from importation into Alaska, there is some straying of escapees from B.C. farms, which could provide an avenue for the virus to enter Alaska waters.
However, ISAv testing by PCR of Atlantic salmon (4,726 tests) from British Columbia farms by the Canadian government during the last 8 years and during the past quarter has been negative for the virus. Therefore, the risk of virus transmission from such escapees, says ADFG, is very low.
For more information on ISAv see: International Response to Infectious Salmon Anemia: Prevention, Control, and Eradication (PDF 1,121 kB)