About Clonorchis

What is Clonorchis?

Clonorchis is a liver fluke parasite (trematode or worm) that can infect the liver, gallbladder, and bile duct. Found across parts of Asia, it is also known as the Chinese or oriental liver fluke.

What are the signs and symptoms of infection with Clonorchis?

Most infected persons have no symptoms. In mild cases, symptoms may include indigestion, abdominal pain, diarrhea, or constipation. Most signs and symptoms are related to inflammation and intermittent obstruction  of the bile ducts. In severe cases, abdominal pain, nausea, and diarrhea can occur.

Untreated, infection may persist for up to 30 years, the lifespan of the parasite. In infections that last a long time, an enlarged liver and malnutrition may occur. In areas where liver flukes are endemic and a person may have multiple long-standing untreated liver fluke infections, the inflammation of the gallbladder and ducts caused by the parasite has been associated with liver and bile duct cancers, including cholangiocarcinoma. Liver flukes are one of many factors that have been associated with cholangiocarcinoma. Other known risk factors for cholangiocarcinoma include hepatitis B, hepatitis C, alcoholic liver disease and other causes of bile duct inflammation. These risk factors are thought to be more common causes of cholangiocarcinoma in the United States than liver fluke infection. Most patients in Western countries do not have an identifiable risk factor for cholangiocarcinoma.

How does one become infected with Clonorchis?

The eggs of Clonorchis are ingested by freshwater snails. After the eggs hatch, infected snails release microscopic larvae that then enter freshwater fish. People become infected by eating infected raw or undercooked fish containing the larvae. After being ingested by humans, the larvae grow into adult worms and live inside the human bile duct system. The life cycle takes three months to complete in humans. Infected people will then pass eggs in their stool(poop) or may cough them up.

Who is at risk for Clonorchis infection?

Liver fluke infections occur mostly in people living in some areas where the parasites are found. Travelers to Asia who consume raw or poorly cooked fish are at risk for liver fluke infection. Chlonorchis is found in Asian countries including Korea, China, Taiwan, Northern Vietnam, Japan, and Asian Russia. Clonorchis infection has been reported in Asian immigrants in non-endemic areas. Some cases were found in people who had ingested imported freshwater fish (undercooked or pickled) containing parasitic cysts.

What should I do if I think I might be infected?

See your health care provider if you have traveled to a country where Clonorchis parasites are found and think you may have been exposed. Research has shown the liver fluke infections can persist for at most 25–30 years, the lifespan of the parasite.

How is infection with Clonorchis diagnosed?

Diagnosis of Clonorchis infection is based on microscopic identification of eggs in stool specimens. More than one stool sample may be needed to detect the eggs. The eggs of Clonorchis are very similar to those of Opisthorchis, another liver fluke, but can be distinguished by microscopic features. Additionally, cysts containing the parasite can sometimes be detected by ultrasound, CT, or MRI. Testing the blood for Clonorchis is not useful for patient management. No blood test is available in the United States.

Can Clonorchis be transmitted person to person?

No. Clonorchis cannot be directly transmitted from person to person.

How is infection with Clonorchis treated?

Praziquantel or albendazole are the drugs of choice to treat Clonorchis infection.

Patient management

Patients with signs and symptoms of Clonorchis infection or liver disease should see a health care provider.

Ova and parasite (O&P) stool examinations for liver flukes is the only test available for the diagnosis of Clonorchis infection. Stool examination is unlikely to result in a diagnosis in persons whose only exposure to Clonorchis took place more than 25–30 years ago (the life span of a liver fluke). In the absence of detection of liver flukes, there is no test available that can determine if liver fluke infection is the underlying cause of cholangiocarcinoma or other conditions of the liver, bile ducts, or gallbladder.

How can I prevent Clonorchis infection?

Clonorchis infection can be prevented by avoiding raw or undercooked freshwater fish. Lightly salted, smoked, or pickled fish can contain infectious parasites. Clonorchis infection does not result from drinking river water or other non-potable water.

The FDA recommends the following for fish preparation or storage to kill parasites.

  • Cooking
    • Cook fish adequately (to an internal temperature of at least 145° F [~63° C]).
  • Freezing
    • At -4°F (-20°C) or below for at least 7 days (total time); or
    • At -31°F (-35°C) or below until solid, and storing at -31°F (-35°C) or below for a least 15 hours; or
    • At -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for at least 24 hours.

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Page last reviewed: October 21, 2020