Living in the PNW, I've learned that it's not just salmon. It's things like trout too. Anything that lives in or swims up freshwater. Rickettsia is a microorganism that lives inside parasites (flukes, I believe) which live inside snails. The fish, traveling through the freshwater, eat the snails and are then carrying the microorganism, Rickettsia, which is what causes the salmon poisoning disease. Not all of the parasites are going to cause SPD. It's the ones carrying parasites that are, in turn, carrying the microorganism.
I've come to be more knowledgeable on SPD than I was before because we recently bought a box of mackerel at our local grocery store. It stocks up on mackerel every year because people love to use it as crab bait. We just let some kidney and turkey necks go rotten and use the mackerel for dog food! Anyhow, we opened up this box of "mackerel" and it was definitely NOT mackerel. I know what mackerel look like and these were very obviously freshwater fish. Turns out they were bangus (also known as milkfish). These are from the Philippines and can cause something very similar to SPD. Same process, even. The flukes are infected with a microorganism and latch onto fish which are then eaten by dogs. Although, with this one, unlike SPD, dogs, cats, humans, and a few other species can be infected. With SPD, only canines are at risk which is why bears, raccoons, etc. can eat salmon without issue.
Anyhow, I know fish was only mentioned, but I thought it was worth bringing up since only salmon was pointed out as being risky to feed.
Correct, both trout and salmon (closely related species) from the NW carry a SPD risk.
Those Phillipine milkfish are the most boney fish I've ever consumed. Sharp little bones too. They are kinda tastey, but bones, bones. bones!