Salmon Poisoning is a unique disease in dogs that is really only found in the Pacific Northwest. The term “Salmon Poisoning” is somewhat misleading, as the disease is not a true poisoning and not a problem from the fish meat itself. Salmon poisoning is actually an infection found in dogs that occur through a complex life cycle involving a bacteria (Neorickettsia helminthoeca), a fluke parasite (Nanophyetus salmincola), a snail (Oxytrema silicula), certain fish, and dogs. The infection is caused by a small bacterial organism that lives in a fluke parasite. The fluke lives only in one known species of snail found in the Pacific Northwest coastal freshwaters. The flukes mature within the snail, and when released, infect fish that spawn in fresh water. The fish involved spend part of their life in salt water (salmon, certain trout, steelhead, and one species of salamander). The bacteria cause no known illness in the fish. Dogs become infected after eating raw fish harboring the fluke, which carries the bacteria. Once in the dog intestinal tract, the bacteria are released causing infection. The bacteria do not affect cats.
Signs of infection occur approximately one (1) week later. Vomiting, diarrhea, fever, and enlarged lymph nodes are often found. In my experience, the diarrhea is very orange(pumpkin) in color. The disease can be life threatening if left untreated. Diagnosis can be based on finding evidence of the fluke eggs on a fecal examination, or finding the bacterial organism on aspiration of the lymph nodes. Therapy involves addressing hydration, nausea, anti-parasitic medication for the fluke, and antibiotics for the bacteria. The antibiotic used is not one chosen for other causes of vomiting and diarrhea so the diet history is very important in diagnosis.
ACCES Renton has seen an increased number of cases over last year, which likely has to do with our proximity to salmon runs along the Green and Cedar Rivers. Cases likely fluctuate based on the size of the salmon run, temperature of the river, seasonality of the salmon migrations, and other local factors that may encourage the growth of the fluke or snails.
We had one case in which crows or seagulls left salmon carcasses in the yard of a dog with no other exposure to salmon. In another instance, two dogs drank water from a cooler that held salmon, but did not actually eat any salmon. Another case was from feeding smoked, uncooked salmon to a family pet. (Cooking kills the disease causing organism.) This is often where the confusion regarding a poisoning/toxicity comes from. It is often thought that the salmon has “gone bad” and is releasing toxins like what one would see with conditions such as botulism, food poisoning from E. coli, or salmonella toxicity. Though vomiting a diarrhea may occur due to ingestion of decaying, rotting salmon, “Salmon Poisoning” is a specific disease that occurs from specific bacteria, which may not be carried by every salmon, in all locations.
Raw or undercooked salmon should not be fed to dogs. If your dog, develops severe vomiting or diarrhea they should always be evaluated by a veterinarian. Always give your veterinarian a thorough diet and travel history as this helps pinpoint what the cause of illness may be.