Wild sockeye salmon from B.C.'s Rivers Inlet have tested positive for a potentially devastating virus that has never been found before in the North Pacific.

Infectious salmon anemia is a flu-like virus affecting Atlantic salmon that spreads very quickly and mutates easily, according to Simon Fraser University fisheries statistician Rick Routledge.

ISA can be fatal to Atlantic salmon, especially those confined in fish farms. Its effect on wild sockeye is unknown.

The virus detected in sockeye smolts by the Atlantic Veterinary College in P.E.I. — Canada's ISA reference lab — is the European strain of ISA, the same virus that devastated fish farms in Chile four years ago.

"It is described as highly contagious and lethal," said Routledge, who had underweight Pacific sockeye sent for testing at the suggestion of B.C. salmon biologist Alexandra Morton.

Of the 48 fish sent for testing, two were found to have the virus.

Morton had raised concerns about the possible presence of the virus in B.C. after seeing Ministry of Agriculture and Lands disease reports describing "classic" ISA-like lesions in farmed salmon. An investigation by the Canadian Food Inspection Agency found no risk of ISA at the sites identified by Morton, who dismissed the inquiry as "little more than a phone call."

More than 4,700 tissue tests for ISA were conducted on B.C. farmed salmon over the past eight years and every one has come back negative, according to Ian Roberts, a spokesman for B.C.'s largest salmon farming company, Marine Harvest. Another 65 tests conducted in the past quarter were also negative.

"As far as we know [Marine Harvest] is clean of this disease and we want to keep it that way," said company environmental officer Clare Backman. "Just because it is present in these Pacific salmon doesn't mean it's a health issue ... Pacific salmon are not as affected by ISA as Atlantic salmon."

ISA has been found in wild Atlantic salmon in Nova Scotia's Bay of Fundy, a fish population that is depressed and on the verge of extinction, Routledge said.

"There is really no information on the impact it could have on Pacific sockeye salmon, which is where we found it," he said.

Like the flu in humans, ISA can exist in a relatively benign form and then mutate into a more deadly version of itself, Routledge said.

The juvenile fish that tested positive were migrating down Rivers Inlet, a sport fishing destination 100 km north of Vancouver Island, from Owikeno Lake. The smolts likely contracted the disease from adult spawners returning to the lake or from their parents, Routledge opined.

"That means the virus has been around for several years," he said. "The only plausible source of this virus is fish farms."

DNA testing on the virus could help determine its source, he said.

B.C.'s aquaculture industry has imported more than 30 million Atlantic salmon eggs over the past 25 years, mainly from Iceland, the United States and Ireland, according to the Department of Fisheries and Oceans.

ISA is usually found in Atlantic salmon, though it can also infect herring. The virus devastated fish farms in Chile in 2007 and 2008, killing millions of fish and resulting in the closure of both fish farms and processing plants. Fish farms in Scotland and Norway have also suffered lethal outbreaks, according to Morton.

"The New York Times reported from Chile that the Chilean aquaculture industry suffered more than $2 billion in losses," Morton said. An investigation by scientists from the University of Bergen concluded that Atlantic salmon eggs imported to Chile from Norway were likely the source of the virus.

Suspected cases of ISA must be reported to the Canadian Food Inspection Agency under new regulations introduced in January 2011. Confirmed cases must be reported to the World Organisation of Animal Health.

The CFIA is investigating the P.E.I. lab's positive test results, but has not yet confirmed the diagnosis of ISA.

rshore@vancouversun.com