Atlas of foodborne infections
transmitted by contaminated food and water

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Nanophyetus salmincola

CZ:
EN: fish flu

Occurrence:
Fish and Fish Products


Category:
Parasites


Foodborne Disease:
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nanophyetiasis - "fish flu" -  diarrhoea, circulating eosinophils, abdominal discomfort and nausea

N. salmincola is responsible for the transmission of Neorickettsia helminthoeca, which causes an illness in dogs that may be serious or even fatal.


Description:
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Nanophyetus salmincola or N. schikhobalowi are the names, respectively, of the North American and Russian troglotrematoid trematodes (or flukes). These are parasitic flatworms. Nanophyetiasis is the name of the human disease caused by these flukes. At least one newspaper referred to the disease as "fish flu." N. salmincola is responsible for the transmission of Neorickettsia helminthoeca, which causes an illness in dogs that may be serious or even fatal.

Knowledge of nanophyetiasis is limited. The first reported cases are characterized by an increase of bowel movements or diarrhoea, usually accompanied by increased numbers of circulating eosinophils, abdominal discomfort and nausea. A few patients reported weight loss and fatigue, and some were asymptomatic. The rickettsia, though fatal to 80% of untreated dogs, is not known to infect humans.

Detection of operculate eggs of the characteristic size and shape in the faeces is indicative of

nanophyetiasis. Nanophyetiasis is transmitted by the larval stage (metacercaria) of a worm that encysts in the flesh of freshwater fishes. In anadromous fish, the parasite's cysts can survive the period spent at sea. Although the metacercaria encysts in many species of fish, North American cases were all associated with salmonids. Raw, underprocessed, and smoked salmon and steelhead were implicated in the cases to date.

Mebendazole was ineffective as a treatment; patients kept shedding eggs, and symptoms gradually decreased over 2 months or more. There are no tested methods for detection of Nanophyetus spp. in fishes. Candling with the aid of a dissecting microscope, or pepsin HCl digestion should detect heavily infected fish.


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