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For further information, see CMDT Part 35–15: Clonorchiasis & Opisthorchiasis

Key Features

  • Clonorchiasis and opisthorchiasis are clinically indistinguishable

  • Parasite eggs are shed into water in human or animal feces, where they infect snails, which release cercariae, which infect fish

  • Human infection follows ingestion of raw, undercooked, or pickled freshwater fish containing metacercariae

  • These parasites excyst in the duodenum and ascend into the biliary tract, where they mature and remain for many years, shedding eggs in the bile

  • Clonorchiasis

    • Infection by Clonorchis sinensis, the Chinese liver fluke, is endemic in areas of

      • Japan

      • Korea

      • China

      • Taiwan

      • Southeast Asia

      • Far eastern part of Russia

    • An estimated 15 million people are infected (13 million in China)

    • In some communities, prevalence can reach 80%

  • Opisthorchiasis caused by

    • Opisthorchis felineus (regions of the former Soviet Union)

    • Opisthorchis viverrini (Thailand, Laos, Vietnam)

Clinical Findings

  • Most patients harbor few parasites and are asymptomatic

  • Acute illness

    • Can occur 2–3 weeks after initial infection

    • Symptoms and signs

      • Fever

      • Malaise

      • Abdominal pain

      • Anorexia

      • Tender hepatomegaly

      • Urticaria

      • Eosinophilia

  • In chronic heavy infections, findings include

    • Abdominal pain

    • Anorexia

    • Weight loss

    • Tender hepatomegaly

  • More serious findings can include

    • Recurrent bacterial cholangitis and sepsis

    • Cholecystitis

    • Liver abscess

    • Pancreatitis

    • An increased risk of cholangiocarcinoma has been documented


  • Early diagnosis is presumptive, based on clinical findings and epidemiology

  • Subsequent diagnosis is made by finding characteristic eggs in stool or duodenal or biliary contents

  • The acute syndrome is difficult to diagnose, since ova may not appear in the feces until 3–4 weeks after onset of symptoms

  • The stool Kato-Katz test is widely used; performing repeated tests improves sensitivity

  • Imaging studies show characteristic biliary tract dilatations with filling defects due to flukes

  • Serologic assays for clonorchiasis with excellent sensitivity are available but cannot distinguish between past and current infection

  • Molecular tests have been developed but are not widely used


  • Praziquantel

    • Drug of choice

    • Dosage: 25 mg/kg orally three times daily for 2 days

      • Provides cure rates > 90%

      • Provides egg reduction rates of nearly 100%

    • One day of treatment may be sufficient

    • Re-treatment may be required, especially in some areas with known decreased praziquantel efficacy

  • Albendazole

    • Second-line drug

    • Dosage: 400 mg orally twice daily for 7 days, which appears to be somewhat less effective

  • Tribendimidine

    • Approved in China

    • Has shown efficacy for clonorchiasis similar to that of praziquantel

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