Salmon Poisoning Disease is one of the only veterinary diseases we see that is specific to the Pacific Northwest. It is serious (as this viewer has shared) -- with a nearly 90 percent fatality rate in untreated dogs. While we commonly refer to this disease as a 'poisoning', it is not related to a toxin within salmon, and in fact isn't isolated to salmon at all. Any anadromous fish (a fish that lives in saltwater, but spends some of its life in freshwater) can host the organism that causes Salmon Poisoning (as can the Pacific Giant Salamander).
First the specifics. Salmon Poisoning is a condition caused by a bacterial organism (Neorickettsia helminthoeca) very similar to those that cause Rocky Mountain Spotted Fever and Typhus. It is specific to dogs (domestic, wolves, coyotes), so other household pets (cats, rabbits) and people are not at risk of contracting it. Once in the dog's intestines, the organism spreads to the lungs, liver, brain and lymphoid tissue, with clinical signs showing up about a week after infection.
But the bacterial organism that causes the disease is one player in a really complicated life cycle. The bacterial organisms live in the tissue of a fluke (a kind of worm) found in freshwater. Larval forms of these fluke must infect a certain snail, where they undergo developmental changes, and then get released back into the water. This form of the fluke can then penetrate the skin of certain fish, where they form cysts within the tissues of the fish. The cysts "hang out" in the fish, until eaten by a dog, and emerge as adults in the dog's intestines (shedding the Neorickettsial organism, leading to "Salmon Poisoning").
The specifics of this life cycle have always amazed me -- ONE certain fluke, ONE certain snail, a handfull of host fish, and a DOG. Who comes up with this stuff?
So to become infected, a dog needs to eat fish with the encysted flukes -- this is usually raw fish, although smoking fish appears to not harm the fluke cysts as much as cooking does (and is therefore a risk for our canine companions). We can typically link infection to visiting a beach or river, during which time the dog eats a dead infected fish (but raw fish from the grocery store or something caught locally can also be infected and pose a concern).
Signs of the disease are fairly non-specific: the dog may become lethargic and stop eating or develop a fever. Some get diarrhea or vomit, and enlarged lymph nodes can sometimes be felt. Diagnosis often relies on known exposure to raw fish, although in most cases the egg of the infective fluke can be detected in the dog's feces. Treatment with intravenous antibiotics, IV fluids, and nutritional support are needed to kill the bacterial organism and correct the damage it causes -- some dogs may even need a blood transfusion. The fluke can be killed with one of many available 'dewormers' available to veterinarians.
Prevention focuses on eliminating exposure to raw fish -- both wild and human-source. Make sure your dog is not consuming anything it finds on the beach, and certainly avoid feeding raw or smoked salmon (trout, steelhead...) products at home (as treats, or as part of a home made raw diet). And as always -- if something seems not right, talk with your veterinarian immediately. Early intervention can have a profound impact on recovery from this