47 - Neorickettsiosis

Abstract

•Cause: Neorickettsia helminthoeca, the Stellantchasmus falcatus (SF) agent/Elokomin fluke fever (EFF) agent (salmon poisoning disease [SPD]) and Neorickettsia risticii. All are gram-negative, obligately intracellular bacteria that belong to the family Anaplasmataceae. A related organism, Neorickettsia sennetsu, causes febrile illness in humans who ingest raw fish in Asia (Sennetsu fever).•First Described: The first reports of SPD were from northwestern Oregon, United States, in 1814 (Astoria). Reports of natural infection of dogs with N. risticii first appeared from the United States in 1994.•Affected Hosts: Neorickettsia helminthoeca infects dogs, foxes, coyotes, raccoons, and captive bears. The SF agent infects dogs. Neorickettsia risticii infects horses (causing Potomac horse fever or equine neorickettsiosis), bats, and dogs. In addition, experimental transmission to dogs and cats has resulted in disease.•Intermediate Hosts: The intermediate hosts for N. helminthoeca and probably the SF agent are aquatic snails (Oxytrema silicula) and fish (especially salmonids). For N. risticii, they are aquatic snails (Juga and Elimia spp.) and aquatic insects (caddisflies and mayflies).•Geographic Distribution: The distribution of SPD is limited to the coastal areas of Washington, Oregon, northern California, British Columbia, and Brazil (2004). Infections with N. risticii have been documented in horses from the United States, Canada, and South America, including Uruguay and Brazil.•Route of Transmission: SPD is transmitted to dogs by ingestion of the infected trematode vector Nanophyetus salmincola, most often in salmonid fish. Neorickettsia risticii is transmitted to horses by ingestion of the trematode vector Acanthatrium oregonense within aquatic insects. The mode of transmission of N. risticii to dogs is unknown, but they also may become infected through ingestion of infected aquatic snails or insects.•Major Clinical Signs: SPD is often associated with fever, lethargy, anorexia, vomiting, diarrhea, and lymphadenomegaly. In the rare reports of N. risticii infection, dogs and cats have shown signs of lethargy, vomiting, hematemesis, petechial hemorrhages, fever, and polyarthritis.•Differential Diagnoses: These include lymphoma, CPV infection, CDV infection, granulocytic anaplasmosis, ehrlichiosis, leptospirosis, septic shock, disseminated fungal disease (especially cryptococcosis), hemorrhagic gastroenteritis, dietary indiscretion, GI foreign body, pancreatitis, hypoadrenocorticism, and inflammatory bowel disease. For SPD, appropriate antimicrobial treatment with doxycycline must begin before the diagnosis is confirmed by laboratory testing. Misdiagnosis and delayed or inappropriate antimicrobial drug therapy increase morbidity and mortality.•Human Health Significance: Nanophyetus salmincola can cause GI disturbances and eosinophilia in humans, but N. helminthoeca does not cause human disease. Similarly, N. risticii has not been reported to cause human disease. Neorickettsia sennetsu is a related pathogen that causes febrile illness in humans consuming raw fish in Asia.