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so this virus does cannot cause disease that can kill salmon? please clarify.
It’s been a matter of debate for awhile. Although PRV is strongly correlated to HSMI it doesn’t necessarily result in disease. The mode how it actually can causes disease is not entirely clear. PRV is ubiquitous in farmed Atlantic salmon, but they all don’t get HSMI just because they have PRV. If you read the literature on it you will find that Atlantic salmon can have high concentrations of PRV but never develop signs of HSMI. Other research has shown that wild salmonids from here to Alaska have likely had PRV since the 70s. Wild salmonids here in B.C. have been shown to have PRV but show no clinical signs of HSMI.
Researchers here in a recent study (Kyle Garver is the scientist who with other researchers looked into this) injected wild salmon with PRV and held them for several weeks and none developed HSMI. Recent work shortly afterwards with Kristy Miller did find what they believe was HSMI on this one farm under study. The authors from that study believe that HSMI could have been missed before during routine sampling of morts because the window when it occurred is not very obvious with current techniques. One also has to understand that this particular farm was heavily studied so the likelihood to find HSMI was much better. Obviously, it’s not practical to conduct an intensive study like this on each fish farm to find HSMI, but likely better diagnostic technology will be adopted that doesn’t require a research team to spend a whole year studying one farm.
It’s important to note that the presence of HSMI has only been found in farmed Atlantic Salmon - not wild Pacific Salmon. Even in Norway, where this is apparently a big problem according to industry critics, there is no evidence that wild salmon there have HSMI. So far, this has been found in farmed Atlantic Salmon. Not very surprising as most fish health work has been with cultured fish including those in aquaculture. Doing fish health work on wild salmon comes with challenges. It is thought that the quality of fish husbandry in aquaculture can influence whether HSMI develops or not. This makes sense considering that stress and environmental factors are known to leave the host more vulnerable to disease. So, when I see a media article that says PRV is deadly to wild salmon I have to ask the question where is this evidence. It doesn’t mean that it can’t impact wild salmon, but theories of what PRV is doing to wild salmon doesn’t equate necessarily to fact unless it can be demonstrated and documented.