Case of the month #12
by Carolina Azevedo (DACVP)
A 3 year old, male neutered Belgian Malinois presented for a 4 day history of anorexia and a recent onset of progressive vomiting. The owners reported the patient is a known indiscriminate eater and is allowed free range to acreage at his home, and a stream runs through the property where fish often swims.
Digital slides from a fine needle aspirate sample of an enlarged mesenteric lymph node were submitted for evaluation.
What’s your diagnosis?
Fig 1A-F Mesenteric lymph node, Diff Quik, images captured with Zoetis Vetscan Imagyst®, 20-40x magnification
The sample was of moderate to high cellularity with mild blood contamination in a clear to pale blue, hazy background. Nucleated cells consist of predominantly lymphoid cells, with a mild to moderate macrophagic infiltrate and fewer neutrophils. The lymphoid population is heterogenous and consists of mostly small, mature lymphocytes, with a moderate expansion to intermediate and large cells and a concurrent moderate plasmacytosis. Macrophages occasionally to often contain numerous individual and clumped basophilic <1-µm diameter structures consistent for neorickettsial organisms.
Reactive lymphoid hyperplasia with macrophagic rich infiltrate and presence of intra-histiocytic structures consistent for neorickettsial organisms
Salmon poisoning disease is an infectious disease caused by the obligate intracellular bacterium Neorickettsia helminthoeca, which is carried as an endosymbiont within all stages of the flatworm vector Nanophyetes salmincola. The geographic region most commonly associated with Salmon poisoning disease is the North American Pacific Northwest, to include Northern California, Oregon, Washington State, and south Vancouver Island. This geographic radius is thought to most likely be due to the endemic range of the snail Julga silicule, which is the first intermediate host of the aforementioned fluke vector, Nanophyetes salmincola. However, Salmon poisoning disease has also been reported in two dogs in Southern Brazil. Fish, particularly salmonids serve as the second intermediate host for the trematode. Dogs serve as a definitive host and are infected following ingestion of metacercariae-infected raw or undercooked salmon, steelhead, trout, or pacific giant Salamanders. Other canids (i.e. wolves, foxes, coyotes) and bears may also serve as definitive hosts. Following ingestion, the trematode matures during an incubation period of 5-6 days and adheres to the intestinal mucosa, with subsequent inoculation of Neorickettsia helminthoeca into the host. The bacterium then replicates within reticuloendothelial cells of the intestine, spleen, Peyer’s patches, and lymph nodes; resulting in a granulomatous inflammatory response. Spread through the circulatory and lymphatic systems results in further bacterial dissemination.
Clinical signs of salmon poisoning include lymphadenomegaly, weight loss, pyrexia, inappetence, diarrhea, vomiting, dehydration, and lethargy in addition to possible neurologic signs. Affected dogs are frequently exhibit thrombocytopenia, lymphopenia, and neutrophilia and may demonstrate a left shift and/or toxic change within the neutrophil population. Common reported biochemical abnormalities include hyponatremia, hypocalcemia, hypoalbuminemia, and increased alkaline phosphatase activity. Altered coagulation profiles may also be noted. On imaging, generalized abdominal lymphadenopathy is typically observed, in addition to possible splenomegaly, hepatomegaly, and/ or gastrointestinal wall thickening.Â
A cytologic diagnosis of salmon poisoning is possible with fine needle aspirate samples of affected lymph nodes and identification of the characteristic intra-cytoplasmic organisms within histiocytes. Further diagnostic corroboration in patients with supporting clinical signs could include submission of feces for fecal floatation and/ or fecal sedimentation to evaluate for Nonophyetus salmincola ova in addition to PCR-based assays of lymphoid tissue for Neorickettsia helminthoeca.
Treatment of salmon poisoning typically involves supportive therapy and tetracycline antibiotics; with praziquantel commonly used for treatment of the fluke infestation. The mortality rate is approximately 90% when the condition is left untreated, with most affected animals dying within 6-10 days following onset of clinical signs.
If you want to know more about this condition, check out these free links:
https://pubmed.ncbi.nlm.nih.gov/20337917/
https://pubmed.ncbi.nlm.nih.gov/36475066/
Sykes JE, Marks SL, Mapes S, Schultz RM, Pollard RE, Tokarz D, Pesavento PP, Lindsay LA, Foley JE. Salmon poisoning disease in dogs: 29 cases. J Vet Intern Med. 2010 May-Jun;24(3):504-13.
Headley SA, Scorpio DG, Vidotto O, Dumler JS. Neorickettsia helminthoeca and salmon poisoning disease: a review. Vet J. 2011 Feb;187(2):165-73. doi: 10.1016/j.tvjl.2009.11.019.
Furtado AP, Cohen H, Handa A, Wardrop J, de Souza C. Salmon poisoning disease in dogs: clinical presentation, diagnosis and treatment. Braz J Vet Med. 2022 Dec 1;44:e004822