A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>

Date: Wed 30 May 2012
Source: Peninsula Daily News [edited]

A deadly fish virus known to affect wild salmon has hit a Peninsula fish farm, forcing American Gold Seafoods to kill the entire stock of Atlantic salmon it had at its Bainbridge Island site, and triggering concerns of a possible spread of the disease among fish in the Salish Sea.

Tests earlier this month [May 2012] confirmed the presence of an influenza-like virus called infectious hematopoietic necrosis, or IHN, in the fish contained in 2 acres [0.8 ha] of nets near the shores of Bainbridge Island.

The virus does not affect humans but occurs in wild sockeye salmon and can be carried by other fish, such as herring, that sometimes pass through fish net pens, affecting the farmed fish.

It first appeared in 2 British Columbia fish farms, forcing the destruction of almost 600 000 fish, the Kitsap Sun reported.

Tests on the Bainbridge fish came back positive for the virus this month [May 2012], after fish farm employees noticed a higher than usual die-off in April.

American Gold Seafoods, affiliated with Icicle Seafoods of Seattle, operates 2 hatcheries near Rochester, and has 120 pens off Port Angeles, Bainbridge Island, Cypress Island, and Hope Island in Puget Sound.

The company's Port Angeles pens are on Ediz Hook, near the Coast Guard Air Station/Sector Field Office Port Angeles.

No company representatives answered phones at the Port Angeles hatchery Sunday [26 May 2012], but the company website <http://www.americangoldseafoods.com> lists the pens at Port Angeles as being "juvenile pens."

John Kerwin, fish health supervisor for the Washington Department of Fish and Wildlife, said the virus is a big concern. "Any 1st time it occurs, you don't fully understand the impact to wild fish," Kerwin said. "We know it can impact (farm) fish. If we move fast, we can try to minimize the amplification."

American Gold Seafoods plans to remove more than a million pounds of Atlantic salmon from infected net pens in Rich Passage off the southern tip of Bainbridge Island.

"It's a very, very big loss for us," Alan Cook, Icicle's vice president of aquaculture said. "We'll clean up and start again." The company plans to remove all dead or dying fish by the end of June 2012. Nets from 2 acres' worth of pens will be removed and disinfected. The fish farm could be running again in 4 months.

Cook said the company has increased monitoring of net pens in Clam Bay near Manchester in Puget Sound, which is about a half-mile from the infected pens.

The recent outbreaks have prompted Washington-based Wild Fish Conservancy to call for tougher testing rules and limits on net pen salmon aquaculture.

Even though the virus occurs naturally in Northwest salmon, the group worries that densely packed fish farms can amplify the virus's spread, foster its mutation, and infect wild fish that pass in or near the pens.

Cook said his company is taking the virus seriously. Its plan to remove all the farm's fish is not required by law, he said. "It's good husbandry to limit the risk to other fish," he said. "We're not letting the situation sit and fester and then explode."

Adding another disease outbreak to the list of threats to wild salmon concerns local fishermen. "They have enough problems right now," said Curtis Reed, manager of the Waters West Fly Fishing Outfitters in Port Angeles.

Local fishermen are more concerned with the sea lice problem in salmon, which is concentrated by the salmon in pens and then can infect young wild salmon as they pass by the pens on their way out to sea, Reed said.

"Wild fish are unique and pretty special," he said.

[Byline: Arwyn Rice]

Communicated by:

[IHN virus is a rhabdovirus that causes acute, systemic disease in salmonid fish and also occurs in asymptomatic fish hosts. The virus is currently endemic throughout the Pacific Northwest of North America, with a contiguous range extending from Alaska to California and inland to Idaho. Within this geographical area the host range of IHNV includes 5 species of Pacific salmon, Atlantic salmon, and several trout species. The 1st reported epidemics of IHNV occurred in sockeye salmon (_Oncorhynchus nerka_) fry at Washington and Oregon fish hatcheries during the 1950s.

Because farmed salmon are kept at high densities, stress and high pathogen density may act in synergy predisposing the fish to develop clinical disease. As the virus is native to that region, farmed salmon infected with IHNV does not seem to represent a major concern for native wild populations, as would a foreign virus such as infectious salmon anemia. Portions of this comment were extracted from Kurath et al. (2003; J Gen Virol 84: 803-14).

Bainbridge Island, Washington may be found on the HealthMap/ProMED-mail interactive map at <http://healthmap.org/r/2t9u>. - Mod.TG]

[see also:
Infectious hematopoietic necrosis - Canada: (BC) 20120518.1137106
Infectious hematopoietic necrosis, trout - Czech Rep.: OIE
Infectious hematopoietic necrosis, trout - USA (OR) 20040626.1711
Infectious hematopoietic necrosis, trout - Austria 20030701.1622 Infectious hematopoietic necrosis, trout - USA (OR) 20030606.1395
Infectious hematopoietic necrosis, salmon - USA 20020721.4825
Infectious hematopoietic necrosis, fish - France 19990303.0306
Infectious hematopoietic necrosis - Belgium 19970903.1879] .................................................sb/tg/mj/dk/ll

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