My dog, Kessa died from it when I was in Oregon about 6 years ago.
It is a terrible disease & yes it is only the salmon that are in the northwest and if I remember correctly it only affects the salmon in 2 rivers and no where else.
it is salmonila poisoning, the symptoms are very similar to parvo.
And it is only with raw salmon, not cooked.

She was THE BEST dog I have ever ever had. half rott half husky, looked just like rott but with a tiny bit longer fur, not too long though, and she had ice blue eyes. So smart. I miss that girl.
We drove her to CA & burried her in the redwoods.