It's only salmon caught in specific areas. Some salmon carry a fluke parasite that can be dangerous. I believe the affected fish are mainly found in the Pacific off the coast of California and Oregon.

It does not affect salmon caught in Northern waters. There are thousands of dogs up here who exsist on nothing but chum salmon and are just fine. There is actually a set time when people can fish for dog food fish. (chum salmon have already spawned and aren't fit for human consumption anymore) My own dogs eat plenty of salmon and have never had a problem with it.

Here's a link with more info:
http://www.phouka.com/dogs/dog_salmon.html