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Heterophyiasis and Related Trematode Infections

(Intestinal Fluke Infection)

By

Chelsea Marie

, PhD, University of Virginia;


William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Last full review/revision Aug 2021| Content last modified Aug 2021
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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, gastrointestinal tract, lungs, liver) depending on the species.

Heterophyes heterophyes is endemic in East Asia, the Middle East, Sudan, Egypt, and southeast Europe.

Heterophyiasis 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. Flukes may penetrate the mucosa and deposit eggs that pass through lymphatics into the bloodstream. Egg migration to the heart and other organs has been reported.

Infection with Metagonimus yokogawai, a related trematode, has been reported after eating raw or undercooked freshwater or brackish fish in Far Eastern Russia, Korea, Japan, China, Taiwan, the Balkan states, Israel, and Spain. Intestinal infection with Nanophyetus salmincola has been reported after ingestion of raw or undercooked salmon.

Infections are frequently asymptomatic. Symptoms are more common with heavy infections or in immunocompromised patients. Onset of symptoms is typically about 9 days after ingestion of contaminated fish and can include anorexia, nausea, abdominal pain, malabsorption, weight loss, dyspepsia, and diarrhea. Eosinophilia may be present.

Adult flukes can cause abdominal pain and diarrhea.

Diagnosis of heterophyiasis is by finding eggs (colored yellow-brown and measuring about 30 mcm by 15 mcm) 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 orally 3 times a day for 1 day for H. heterophyes and M. yokogawai and 20 mg/kg orally 3 times a day for 1 day for N. salmincola.

Prevention involves not eating raw or undercooked fish that may contain these intestinal flukes.

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