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Nanophyetus spp.

June 10, 2008 - 7:30am
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Nanophyetus spp.

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.

What are the symptoms of nanophyetiasis?

Knowledge of nanophyetiasis is limited. The first reported cases are characterized by an increase of bowel movements or diarrhea, 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.

How is nanophyetiasis diagnosed?

Detection of operculate eggs of the characteristic size and shape in the feces is indicative of nanophyetiasis. The eggs are difficult to distinguish from those of Diphyllobothrium latum.

What foods have been associated with nanophyetiasis?

There have been no reported outbreaks of nanophyetiasis in North America; the only scientific reports are of 20 individual cases referred to in one Oregon clinic. A report in the popular press indicates that the frequency is significantly higher.

How common is 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.

Who is susceptible to nanophyetiasis?

Consumers of raw or underprocessed freshwater or anadromous fish, especially salmonids.

How is Nanophyetus detected in fish?

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.


Food and Drug Administration

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