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Microbiology · Trematodes (flukes)

Clonorchis sinensis / Opisthorchis spp. !

  • Parasite
  • For completeness

Liver flukes from raw freshwater fish in Asia. They live for years in the bile ducts and raise the risk of bile duct cancer.

Updated 2026-11-01

Also called: Chinese liver fluke, opisthorchiasis, clonorchiasis

At a glance

Shape
Lancet-shaped, flat and translucent
Family
Opisthorchiidae
Type
Hepatic trematode (bile duct fluke)
Size
Adult 1–2.5 cm

Morphology

  • Small egg (27–35 µm) with a convex operculum resting on 'shoulders'.
  • Small knob at the opposite end; passed already embryonated.
  • Clonorchis and Opisthorchis eggs are practically indistinguishable.

Transmission

  • Eating raw, salted, pickled or smoked freshwater fish with metacercariae.

Reservoir: Humans, dogs, cats and other fish-eating mammals; Freshwater snails and fish as intermediate hosts

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. Embryonated eggs leave in stool and bile; a freshwater snail swallows them.
  2. Inside the snail they multiply and cercariae are released into the water.
  3. Cercariae penetrate freshwater fish and encyst in their flesh as metacercariae.
  4. A person who eats that fish raw, salted or smoked releases the metacercaria in the duodenum.
  5. It climbs through the ampulla of Vater to the bile ducts, matures in a month and lives for years.

Virulence factors

  • Chronic inflammation causes biliary epithelial hyperplasia and periductal fibrosis.
  • Promotes stones, recurrent cholangitis and abscesses.
  • C. sinensis and O. viverrini are classified as carcinogens: cholangiocarcinoma.

Diseases it causes

Clinical picture

  • Light infections are asymptomatic.
  • Heavy loads: fever, right upper quadrant pain, hepatomegaly.
  • Obstructive jaundice or a biliary mass after years of infection.

Diagnosis

  • Small eggs with a shouldered operculum on stool microscopy.
  • Serology in specialised laboratories.
  • Ultrasound or MRCP: dilated bile ducts.
  • Adults found at surgery or after treatment.

Treatment

Praziquantel is the drug of choice; albendazole is an alternative.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Cook freshwater fish thoroughly.
  • Avoid raw freshwater fish dishes in endemic areas.
  • Sanitation so that faeces do not reach ponds and rivers.

Test yourself

Think of the answer, then tap the question to see it.

Which cancer is linked to Clonorchis sinensis and Opisthorchis viverrini?

Cholangiocarcinoma.

How is clonorchiasis acquired?

By eating raw, salted, pickled or smoked freshwater fish with metacercariae.

What is the drug of choice for clonorchiasis?

Praziquantel.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Clonorchiasis (CDC, 2024); Foodborne trematode infections (WHO, 2021).

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Representative model, for educational purposes only.