Merck Manual

Please confirm that you are a health care professional

honeypot link



Chelsea Marie

, PhD, University of Virginia;

William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Reviewed/Revised Aug 2023
Topic Resources

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 that contains infectious metacercariae (encysted stage).

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

Opisthorchis species are found in Thailand, Laos, Cambodia, Vietnam, Germany, Italy, Belarus, Russia, Kazakhstan, and Ukraine (see Centers for Disease Control and Prevention (CDC): Opisthorchis Infection).

The life cycle of Opisthorchis requires both snails and fish. Dogs, cats, and other fish-eating mammals are also definitive hosts. 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).

Opisthorchiasis resembles clonorchiasis Clonorchiasis Clonorchiasis is infection with the liver fluke Clonorchis sinensis. Infection is usually acquired by eating undercooked freshwater fish. Most infections are asymptomatic, but when present... read more Clonorchiasis and the development of symptoms depends on worm burden and duration of infection. Most O. viverrini infections remain asymptomatic, with about 5 to 10% of patients presenting with symptoms that include right upper quadrant abdominal pain, indigestion, diarrhea, flatulence, and fatigue. Acute symptoms are more common with O. felineus infection and can include high-grade fever, anorexia, nausea, vomiting, abdominal pain, malaise, myalgia, arthralgia, and urticaria. Symptoms typically begin 10 to 26 days after exposure.

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

The treatment of choice for opisthorchiasis is one of the following:

  • Praziquantel 25 mg/kg orally 3 times a day for 2 days

  • Albendazole 10 mg/kg orally once a day for 7 days

Infection can be prevented by cooking freshwater fish.

General references

  • 1. Xia J, Jiang SC, Peng HJ: Association between liver fluke infection and hepatobiliary pathological changes: A systematic review and meta-analysis. PLoS One 10 (7):e0132673, 2015. doi: 10.1371/journal.pone.0132673

  • 2. Psevdos G, Ford FM, Hong S-T: Screening US Vietnam veterans for liver fluke exposure 5 decades after the end of the war. Infectious Diseases in Clinical Practice 26(4):208–210, 2018. doi: 10.1097/IPC.0000000000000611

Drugs Mentioned In This Article

Drug Name Select Trade
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
quiz link

Test your knowledge

Take a Quiz!