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

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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.

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

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 of opisthorchiasis include vague GI discomfort, diarrhea, and constipation. In chronic infection, symptoms may be more severe; hepatomegaly and undernutrition may be present. Rare complications include cholecystitis, cholangitis, and cholangiocarcinoma.

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

The treatment of choice for opisthorchiasis is

  • Praziquantel 25 mg/kg po tid for 2 days

Infection can be prevented by cooking freshwater fish.

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