This is a severe rickettsial disease of dogs and wild canids that requires the presence of several intermediate hosts, including snails, flukes, fish, and mammals. Humans are not affected.
Dogs acquire the infection when they eat raw freshwater or ocean salmon and related species containing encysted flukes that harbor rickettsiae. The disease is limited to the Pacific Northwest. This is because the first intermediate host is a small snail found only in streams along the coasts of Washington, Oregon, and California.
A few days after a dog ingests contaminated fish, the larval fluke matures and attaches to the lining of the dog’s intestines, where it inserts the rickettsial organism into the intestinal tissues. The incubation period is 5 to 21 days.
Illness begins with high fever, followed by hypothermia, loss of appetite, vomiting, diarrhea (usually bloody), and generalized lymph node enlargement. These signs are similar to those of canine distemper and parvovirus. However, a history of eating raw fish suggests a diagnosis of salmon poisoning. Diagnosis may include finding fluke ova in a fecal sample.
Treatment: Death usually occurs in 7 to 10 days in untreated dogs. However, the illness does respond well to intravenous tetracycline. Supportive treatment with IV fluids and blood transfusions for hemorrhagic diarrhea may be required. Praziquantel and mebendazole eliminate intestinal flukes.
Prevention: Do not allow dogs to eat raw fish. Thoroughly cooking fish (or freezing it for 24 hours) destroys encysted flukes and rickettsiae.