Salmon Poisoning Disease is caused by a rickettsia (Neorickettsia helminthoeca, Neorickettsia elokominica) that lives inside a fluke parasite (Nanophyetus salmincola) that can infect trout, salmon, and Pacific giant salamanders in the Pacific Northwest. It is an acute, infectious disease of dogs, transmitted through various stages of the fluke, in a snail-fish-dog life cycle. Dogs become infected by ingesting encysted metacercariae of the rickettsia-infected fluke. The fluke infection itself produces little or no clinical disease in dogs.

While the disease is native to the Pacific Northwest, cases are recognized periodically in the Southwest when lakes are stocked with fish raised in the Northwest. As fisherman in these regions may be unaware of the source of fish in local lakes, they should prevent dogs from ingesting raw fish, even in small amounts. Since 2006, 5 cases have been diagnosed in Southern California and one was fatal.

Signs in dogs can include fever, vomiting, diarrhea with or without blood, severe lethargy, swollen lymph nodes, collapse and occasionally death, if untreated. The disease causes no harm to the fish. Humans who eat raw fish or do not practice good sanitation in preparing fish can become infected by the fluke (but not the bacteria) and typically experience a mild intestinal illness.

Detection of fluke ova on fecal examination supports the diagnosis in~90% of cases. Aspiration of enlarged lymph nodes from dogs suspected of having salmon poisoning disease may be helpful in making a diagnosis, especially if the intracytoplasmic rickettsial bodies of Neorickettsia helminthoeca are observed in mononuclear cells from the lymph node. When diagnosed early, antibiotic treatment and supportive care can aid in recovery.