Salmon poisoning disease is contracted by ingestion of raw or undercooked fish carrying infected trematode parasites, Nanophyetus salmincola. The flukes parasitize fresh water snails predominantly in the Pacific Northwest and northern California. The disease is caused by infection with a rickettsial organism, not by a toxin as the name implies. The infectious agent is Neorickettsia helminthoeca, which replicates within macrophages, causing a granulomatous inflammatory response in the GI tract, lymph nodes, and spleen. Typical presentation is lethargy and inappetence with variable weakness, vomiting, and diarrhea. Other signs may also be present. Peripheral lymphadenopathy is common but not always present. Abdominal ultrasound usually reveals generalized mesenteric lymphadenopathy, and guided fine-needle aspiration of an abdominal lymph node may be diagnostic. Infection can lead to death, and vague signs should not be ignored, especially if the dog has a history of raw fish ingestion. A retrospective study of California cases showed an over-representation of male Labrador Retrievers. Clinicopathologic findings are typically nonregenerative anemia, neutrophilia, lymphopenia, and hypoalbuminemia. Fecal examination, centrifugation fecal flotation or sedimentation, or both will usually reveal the presence of ova. This is good supporting evidence but not conclusive. Observation of intramacrophagic organisms in lymph nodes is often diagnostic but can be confounded by other types of phagocytized material present in the sample. Low numbers of organisms can be missed. Treatment involves supportive therapies with parenteral anthelmintics and antimicrobials. Tetracyclines are the antimicrobials of choice. Reported success with other antimicrobials is variable. Dogs who recover should have immunity unless they encounter a different strain. Preventing dogs from accessing raw fish is recommended.
Links to sections in the MVM:
Salmon Poisoning Disease and Elokomin Fluke Fever
Rickettsial Diseases
References
Greiman SE, Kent ML, Betts J. Nanophyetus salmincola, vector of the salmon poising disease agent Neorickettsia helminthoeca, harbors a second pathogenic Neorickettsia species. Vet Parasitol. 2016 Oct 15;229:107-109. doi: 10.1016/j.vetpar.2016.10.003.
Lin M, Bachman K, Cheng Z, et al. Analysis of complete genome sequence and major surface antigens of Neorickettsia heminthoeca, causative agent of salmon poisoning disease. Microb Biotechnol. 2017 Jul;10(4):933-957. doi: 10.1111/1751-7915.12731.
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