Opisthorchiasis

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).

Opisthorchis Life Cycle

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Image from the Centers for Disease Control and Prevention Image Library.

Opisthorchiasis resembles 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.

In chronic infection, symptoms may be more severe; hepatomegaly and undernutrition may be present. Rare complications include cholecystitis, cholangitis, and cholangiocarcinoma (bile duct cancer) (1). Vietnam veterans who develop cholangiocarcinoma may have been infected with Opisthorchis viverrini or Clonorchis sinensis while they served in Southeast Asia (2).

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:

Infection can be prevented by cooking freshwater fish.

See also the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) information on opisthorchiasis.