Aquaculture for all

Mainstream Canada Farm Tests Positive for IHN Virus

Salmonids Health Biosecurity +2 more

CANADA - During routine fish health tests on the 14 May, Mainstream Canada's Dixon Bay farm tested positive for the Infectious Haematopoietic Necrosis (IHN) virus.

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Third-party lab PCR test results have shown the presence of the virus. Sequencing has confirmed the presence of IHN virus in these fish.

The farm site has been isolated and is currently being prepared for depopulation if the Canadian Food Inspection Agency (CFIA) deem it necessary upon completion of its investigation.

A spokesperson from Mainstream Canada told TheFishSite that as they caught the disease early through routine diagnostic testing the mortalities are still low but it is too early to tell what the cull is likely to be.

The company is following strict protocols to limit the spread of the virus. "As part of our fish health management plan, Mainstream has strict bio-security protocols that are already in place with additional quarantine protocols in the event of a fish health incident. This includes limiting boat movement in and around the site and restricting visitors and contractors," a company spokesperson told TheFishSite.

Mainstream is also following the industry's viral disease management plan which includes industry-wide protocols for limiting the spread of the virus.

"We are very concerned about this fish health event and are taking every step to make sure it is contained and any risks minimised," said Fernando Villarroel, Mainstream Canada's managing director. "This shows our disease monitoring programmes work. We were able to quickly detect IHN while in its early stages and react decisively. Early detection is crucial to minimising the risk in any fish health situation."

The IHN virus is naturally carried by Pacific salmon, trout and herring. Studies show wild Pacific salmon have a natural resistance to the virus and very rarely suffer ill effects from it.

However, the virus causes IHN disease in farmed Atlantic salmon. Since Atlantic salmon are not native to the Pacific coast, they have not had hundreds of years to develop a natural immunity to the virus, like their Pacific cousins. The disease can cause high degrees of mortalities on Atlantic salmon farms if not quickly managed and contained.

"This is the first diagnosis of IHN among farmed Atlantic salmon in BC since 2003. Although IHN kills up to 100 per cent of exposed Atlantic salmon, wild salmon in marine waters are very resistant to IHNV infection," said Gary Marty, fish pathologist for the BC Animal Health Centre.

A lab study (Traxler et al, 1993) demonstrated this resistance under controlled laboratory exposure conditions. 25 virus-free sockeye salmon were added to a tank with 10 IHNV-injected Atlantic salmon. After 37 days, only one of the 25 sockeye salmon died, and the viral load in that fish was low.

In a remote site, the affected farm is unlikely to pose any danger to other farms. The nearest farm is over 3 km away with the next being 16 km away. These farms are all being screened for the disease.

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