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Clonorchis FAQs


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. Signs and symptoms are related to inflammation and blockage of the bile ducts that may come and go. In severe cases, abdominal pain, nausea, and diarrhea can occur.

Untreated, infection may persist for up to 25–30 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, inflammation of the gallbladder and ducts caused by the parasite has been associated with liver and bile duct cancers (bile duct cancer is also called cholangiocarcinoma). Liver fluke infection is one of many factors that have been associated with bile duct cancer. Other known risk factors for bile duct cancer 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 bile duct cancer in the United States than liver fluke infection. Most patients from Western countries who have bile duct cancer do not have an identifiable risk factor.

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 or may cough them up.

Who is at risk for Clonorchis infection?

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

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 up to 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 . Serologic testing (testing the blood) for Clonorchis is not useful for patient management and is not available in the United States.

Can Clonorchis be transmitted from 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.

Examination of the stool for liver fluke eggs 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), as the liver fluke must be alive in order to produce eggs. 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 bile duct cancer (cholangiocarcinoma) or other conditions of the liver, bile ducts, or gallbladder.