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By Richard D. Pearson, MD

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Opisthorchiasis is infection with Opisthorchis viverrini (Southeast Asian liver fluke) or O. felineus (cat liver fluke), which are acquired by eating infected raw or undercooked fish.

Opisthorchiasis due to O. viverrini occurs mainly in northeast Thailand, Laos, and Cambodia; O. felineus occurs mainly in Europe and Asia, including the former Soviet Union. The life cycle of Opisthorchis requires both snails and fish. Human disease resembles clonorchiasis and is acquired by eating raw or undercooked freshwater fish that contains infectious metacercariae (encysted stage). After ingestion, metacercariae excyst and ascend through the ampulla of Vater into the biliary ducts, where they attach to the mucosa and mature. Adult flukes grow to 5 to 10 mm by 1 to 2 mm ( O. viverrini) or 7 to 12 mm by 2 to 3 mm ( O. felineus).

Most infections are subclinical. Symptoms include vague GI discomfort, diarrhea, and constipation. In chronic infection, symptoms may be more severe and may cause hepatomegaly and undernutrition. Rare complications include cholecystitis, cholangitis, and cholangiocarcinoma.

Diagnosis is by finding eggs in the feces. Ultrasonography, CT, MRI, cholangiography, or ERCP may show biliary tract abnormalities.

Praziquantel 25 mg/kg po tid for 2 days is the treatment of choice.

Infection can be prevented by cooking freshwater fish.

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