Dear Sue Farlinger:
Today, Grieg Seafoods is reporting an outbreak of IHN at their Culloden salmon farm near the entrance to the Fraser River. Earlier this year Grieg reported IHN at Ahlstrom. They cancelled that report, but this outbreak less than 5km away makes us wonder if that cancellation was valid.
Cohen Commission Technical Report #1 by Dr. Michael Kent on pathogen threats to Fraser sockeye states: "I designate the following pathogens as potential "HIGH RISK,: IHN virus…The IHN virus is well recognized as a lethal pathogen to fry sockeye salmon in freshwater." Dr. Kent also states: "… recent evidence suggests that there is variability in the virulence of this virus…"
While IHN is a locally occurring virus, your scientist, Dr. Kyle Garver testified at Cohen that a single salmon farm can shed 650 billion infectious viral IHN particles an hour. IHN is a reportable disease and the OIE document on IHN states a few facts we should all be aware of:
Younger fish are the most susceptible to the disease
"once IHNv is introduced into a farmed stock, the disease may become established among susceptible species of wild fish…"
Infection often leads to death in salmon
primary infection is fish to fish (horizontal)
depending on the strain, outbreaks can be chronic or explosive
The only control method is avoidance
Looking at the attached map, if the farm is shedding trillions of viral particles a day, the wild inbound adult sockeye are passing this virus over their gills just before they enter the nursery grounds where last year's sockeye run are rearing as fry. These young fish are not only the most susceptible to IHN, they could also become carriers, spreading it through the North Pacific to other Canadian and US runs, similar to the threat from the European viruses we are tracking.
I am writing to ask who exactly in DFO Fish Health is going to be tracking this virus in the inbound Fraser sockeye passing this infected farm? What lab did this diagnosis? What clade and strain of IHN does this farm have so we can track it as well. What is known about the virulence of the Grieg IHN strain to Fraser sockeye fry?
I look forward to hearing from you. I will follow up with the person in DFO Fish Health who is tracking this outbreak. I will be adding IHN to the list of viruses we are looking for this summer and will keep you informed of my results.
Alexandra Morton and Anissa Reed
Department of Wild Salmon