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Heterophyiasis and Related Trematode Infections

By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

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Heterophyiasis is infection with the intestinal fluke Heterophyes heterophyes, which is acquired by eating infected raw or undercooked fish from freshwater or brackish water.

Flukes are parasitic flatworms that infect various parts of the body (eg, blood vessels, GI tract, lungs, liver) depending on the species.

Heterophyes heterophyes is endemic in the Far East, Middle East, and Egypt.

Infection is acquired by eating infected raw or undercooked fish from freshwater or brackish water containing metacercariae (encysted stage). After ingestion, metacercariae excyst and attach to the mucosa of the small intestine. There, they develop into adults, growing to about 1.0 to 1.7 mm by 0.3 to 0.4 mm.

Infection with Metagonimus yokogawai, a related trematode, has been reported after eating raw or undercooked freshwater or brackish fish in the Far East, Siberia, Manchuria, the Balkan states, Israel, and Spain. Intestinal infection with Nanophyetus salmincola has been reported after ingestion of raw or undercooked salmon.

Adult flukes can cause abdominal pain and diarrhea.

Diagnosis of heterophyiasis is by finding eggs in the feces. The eggs of H. heterophyes are indistinguishable from those of M. yokogawai and similar to those of Clonorchis and Opisthorchis.

Treatment of heterophyiasis is with praziquantel 25 mg/kg po tid for 1 day for H. heterophyes and M. yokogawai and 20 mg/kg po tid for 1 day for N. salmincola.

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