Fishing can be wonderful recreation, but sharing the catch with your dog can be an act of kindness that kills.
Salmon Poisoning Disease is a potentially fatal condition seen in dogs that eat certain types of raw fish. Salmon (salmonid fish) and other anadromous fish (fish that swim upstream to breed) can be infected with a parasite called Nanophyetus salmincola. Overall, the parasite is relatively harmless. The danger occurs when the parasite itself is infected with a rickettsial organism called Neorickettsia helminthoeca. It’s this microorganism that causes salmon poisoning.
Dogs and other animals become infected by ingesting trout, salmon, or Pacific giant salamanders that contain the encysted metacercaria stage of the rickettsia-infected fluke. In the dog’s intestine, the metacercarial flukes excyst, embed in the duodenal mucosa, become gravid adults, and transmit the rickettsiae to monocytes-macrophages.
- (Hemorrhagic) Diarrhea
- Swollen lymph nodes (lymphadenopathy)- 60% of cases
- Discharge from the nose and eyes
- Leukopenia with degenerative left shift (Neutrophilia)
- Thrombocytopenia - 94% of cases
Signs appear suddenly, usually 5–7 days after eating infected fish, but may be delayed as long as 33 days, and persist for 7–10 days before culminating in death in up to 90% of untreated animals.
Diagnosis and Treatment
- Fluke ova are found on fecal examination in ~92% of cases, which supports the diagnosis. The ova are oval, yellowish brown, rough-surfaced, and ~87–97 × 35–55 μm, with an indistinct operculum and a small, blunt point on the opposite end.
- Intracellular organisms have been demonstrated by Romanowsky staining on lymph node aspirates in ~70% of cases.
- PCR testing to detect DNA-specific N helminthoeca (or Neorickettsia genus) is recommended for accurate diagnosis.
- Serologic testing using the N helminthoeca organism has been developed.
- Other causes of fever of unknown origin, generalized lymphadenopathy, vomiting, and diarrhea are differential diagnoses. Currently, the only means of prevention is to restrict the ingestion of uncooked salmon, trout, steelhead, and similar freshwater fish
Sulfonamides are not effective and may exacerbate the clinical disease. Recommended treatment is parenteral oxytetracycline or doxycycline. Oral tetracycline or doxycycline is contraindicated because of impinging GI signs. Animals usually succumb because of dehydration, electrolyte and acid-base imbalances, and anemia. Therefore, general supportive therapy to maintain hydration and acid-base balance, while meeting nutritional requirements and controlling diarrhea, is often essential. Judicious use of whole blood transfusions may be helpful.