Salmon poisoning is also known as salmon disease, salmon poisoning disease (SPD), and Neorickettsia helminthoeca infection. It is an acute, and often fatal, infectious disease of dogs, coyotes, and foxes of the Pacific Northwest. This disease has been found in black bears and Malayan sun bears, but has not been reported in cats.
Despite its name, salmon poisoning does not involve a toxin. Salmon poisoning is an infection that develops when dogs eat raw or undercooked fish (salmon, trout, or steelhead) or Pacific Giant Salamanders that contain a fluke. A fluke, also known as a trematode, is an internal parasite. In this case, the fluke is Nanophyetus salmincola that contains a rickettsial organism called Neorickettsia helminthoeca.
Once the larval flukes reach the dog's intestinal tract, they embed in the dog's duodenal mucosa, and release the rickettsiae. The rickettsial organisms then spread through the bloodstream to the liver, lungs, brain, and lymphoid tissue. Clinical signs include, but are not limited to: fever; nausea; vomiting; bloody diarrhea; weight loss; ascites; nasal and eye discharge; enlarged lymph nodes; tachypnea; dyspnea; tachycardia; twitching; and seizures. Approximately 60 percent of cases have generalized lymph node enlargement. Unless the infection is treated, 50 – 90% of affected animals will die of the infection within 7 to 10 days.
Clinical signs usually begin about one week after the animal eats the infected raw fish, although delays of 33 days have been reported.
Although infected fish can be found in the Pacific Ocean from San Francisco to the coast of Alaska, salmon poisoning is most commonly found in Washington, Oregon, northern California, and southern Vancouver Island (Canada). It is also seen inland, along the rivers of fish migration. The Pacific Northwest has the trematode's first intermediate host, a small snail called Oxytrema plicifer.
Although clinical signs are caused by the rickettsial organisms and not the fluke, presumptive diagnosis is usually made by identifying the fluke’s ova (eggs) in the feces. Ova are identified in 92% of cases. Direct smears of fecal material usually provide sufficient specimens for diagnosis, although other methods can be used.
Lymph node cytology and histopathology may provide a more definitive diagnosis, if necessary.
A history of access to raw fish also aids in diagnosis.
To combat the hemorrhage, necrosis, and infection, affected animals usually need antibiotics, fluid therapy, blood transfusions, antiemetics, antidiarrheals, and anticestodals (drugs that kill flukes).
Many dogs respond well to antibiotic therapy, and resolution of gastrointestinal signs, fever, and thrombocytopenia can occur within 24-72 hours of starting therapy. However, if treatment is not started, death can occur 7-10 days after the onset of clinical signs. In one report, overall mortality rate was 14%. In another study of 43 dogs that were treated with antibiotics, 39 survived.
Dogs should not be allowed to eat raw or smoked-raw fish (salmon, trout, steelhead), or Pacific Giant Salamanders.
Dogs that survive salmon poisoning will be immune to re-infection with the same strain. However, infection with an alternate strain can occur because there is no cross-protection.