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October 30, 2011

Why fish virus spooks scientists


Why fish virus spooks scientists

To understand why scientists were so alarmed last week to see a potentially lethal fish virus surface in two sockeye, consider what happened in South America in 2007. Millions of farmed fish died, cost billions of dollars and drove thousands of people out of work.
Seattle Times environment reporter

Direct link to this Seattle Times article


To understand why scientists were so alarmed last week to see a potentially lethal fish virus surface in two sockeye, consider what happened in South America in 2007.
Atlantic salmon in two sea pens at a fish farm in central Chile struggled that summer with a common bacteria. So workers injected the lethargic fish with antibiotics. Still the salmon developed tumors and lesions. Their livers and kidneys failed. Within weeks more than 70 percent were dead, and other salmon at nearby farms were sick, too.
The fish had contracted a virus, infectious salmon anemia (ISA). The resulting outbreak would kill millions of farmed salmon, cost farmers billions of dollars and drive thousands of people out of work.
No one knows what ISA's arrival would mean for the Northwest. But experts agree it could spell trouble — if it's truly here.
"This is probably the single-most feared virus in the fish industry," said Fred Kibenge, a researcher at the University of Prince Edward Island in eastern Canada.
He should know. Kibenge has led much of the science on ISA outbreaks across the globe. It was also Kibenge who performed the laboratory tests this fall on 48 wild sockeye smolts snared from Rivers Inlet in northern British Columbia. Last week the world learned he'd found trace evidence of a European strain of the ISA virus in two fish. ISA had never been seen before on the Pacific Coast.
Even the biologist who submitted the fish to Kibenge's lab was caught off guard. He said he'd merely been trying to rule out possibilities that could explain why research crews caught so few young fish this year.
"I was quite literally stunned," said Rick Routledge, at Simon Fraser University.
Disease emergency
Virologists from several state and federal agencies called the discovery a disease emergency. Other scientists cautioned that absent signs of an outbreak, or even disease, it remained possible the results were an error. The Canadian Food Inspection Agency has obtained the hearts and carcasses of the smolts and is performing follow-up tests.
But even if the virus' presence is confirmed, it will merely raise new questions.
For starters, it's not clear why a highly contagious virus associated with farms growing Atlantic salmon would appear first in two juvenile wild sockeye 60 miles from the nearest fish farm — especially when it had never surfaced during routine aquaculture inspections.
Between 2003 and 2010, health auditors for the British Columbia Ministry of Agriculture tested 4,726 fresh dead fish on salmon farms and didn't see ISA. Neither did labs in Washington during 50,691 fish-disease tests of farmed and hatchery fish just last year, though the state was primarily looking for other illnesses.
"Is this something that has been here for a long time and we didn't see it? Or is it brand new?" asked Kevin Amos, a veterinarian and pathologist working for the National Oceanic and Atmospheric Administration's aquaculture program. "Sometimes these things can be pretty weird."
And no one can say what harm it could cause.
Appeared in 1984
The pathogen first appeared in Norway in 1984, and since has killed millions of farmed Atlantic salmon from Scotland to Maine. A less virulent strain sickened some farmed coho in South America in 1999. It doesn't affect people and isn't known to have harmed wild salmon. A 2003 lab study found steelhead, chinook, chum and coho resistant to ISA. But the same research said the virus' potential to mutate should not be ignored.
In fact, when ISA was first identified in Europe, gene tests suggested some version of it had been in Atlantic waters for thousands of years. It only became deadly when Norway's salmon-aquaculture industry exploded.
"Until you had a large number of animals close together in captivity, the virus didn't do anything," said Jill Rolland, director of the U.S. Agriculture Department's aquaculture-health program.
Evidence suggests the virus moved to Chile on contaminated fish eggs brought from Europe. Once it reached salmon net pens it spread quickly, moving from farm to farm through water and on workers' boats, boots, clothes and gloves, said Pablo Valdes-Donoso, veterinary fish researcher and graduate student at the University of California, Davis, who worked on Chilean fish farms.
Chile's fish farms are truly industrial, separated in most cases by less than two miles. In many cases, Valdes-Donoso said, farmers didn't tell neighboring businesses their charges were sick. Some research suggests fish then passed the virus down from one generation to the next. The result was disaster.
"It was like some kind of wildfire," Valdes-Donoso said.
The situation in the Northwest is potentially better — and worse. The scale of British Columbia's marine aquaculture is massive by U.S. standards — B.C. farms about 12 times as much salmon as Washington — but still just a fraction of Chile's.
"Our rearing techniques are also dramatically different," said Dan Swecker, a state legislator who runs the Washington Fish Growers Association. Even so, "This should concern all salmon farmers on the West Coast. If there is something out there, then the industry is going to have to take a look at everything we do."
More troubling to wild-fish advocates should be the fact that Chile has no native salmon — and the Northwest is peppered with hatcheries where fish spend lots of time clustered together, an environment that can amplify disease.
Fears virus is new
It's possible the virus has existed for a while in Pacific salmon in some benign form. And ISA is a saltwater disease, while most hatcheries are found in freshwater.
But scientists worry the virus is, in fact, new.
In other words, if you put a novel virus into a new population "that's when you can get disease," said John Kerwin, the Washington Department of Fish and Wildlife biologist who overseas the state's fish farms.
Jim Winton, the Geological Survey scientist who helped determine wild salmon may resist ISA, agreed.
"If this is the first exposure of Pacific salmon to this virus, which we fear it is, that's disturbing," he said. "There may be species that are particularly susceptible. We'd need research where we could expose them to the virus to understand the relative risks of the current strain.
"Then, what we'd really worry about is, 'How long would it be before this virus evolved?' " he asked.
For now, U.S. animal-disease experts are mapping out surveillance plans and epidemiological research. A congressional measure by U.S. Sen. Maria Cantwell, D-Wash., and Alaska Sens. Lisa Murkowski and Mark Begich would encourage federal agencies to make ISA research a priority. It's part of a larger bill the Senate is expected to vote on this month.
Until then, scientists await results from Canadian government tests.
"At this point we're still treating this as a suspect finding — not a confirmed finding," Amos said. "A lot more investigation is needed."
Craig Welch: 206-464-2093 or cwelch@seattletimes.com


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