About Clonorchis

Overview

Clonorchis is a liver fluke (type of parasitic worm) that can infect the liver, gallbladder, and bile duct.

• Clonorchis (also known as Chinese liver fluke disease), is part of the Opisthorchiidae family of liver flukes.
• You cannot get Clonorchis from another person, and you cannot get it from consuming untreated drinking water.
• Clonorchis infections can last for several years (the lifespan of the parasite).

Signs and symptoms

Most people infected with Clonorchis do not have symptoms. When people have symptoms, they are generally gastrointestinal (GI) (related to the stomach or intestines) and can range from mild to severe. Some symptoms relate to inflammation (swelling) of the liver, gallbladder, and bile ducts. Other symptoms are due to intermittent blockage of the bile ducts.

Symptoms and signs can include one or more of the following, depending on the number of flukes and length of infection:

• Indigestion
• Nausea
• Abdominal pain
• Enlarged liver
• Diarrhea
• Constipation
• Fever
• Jaundice (yellowing of the skin)

If left untreated, Clonorchis infection can last for several years (the lifespan of the parasite). A person may have multiple liver fluke infections if they live in areas where liver flukes exist and consume raw or undercooked freshwater fish. Children with heavy infections (a high number of liver flukes) and/or repeated infections are at risk for malnutrition.

Longstanding inflammation due to Clonorchis infection is associated with bile duct cancer (also known as cholangiocarcinoma). More common risk factors for cholangiocarcinoma in the US include:

• Hepatitis B
• Hepatitis C
• Alcoholic liver disease

However, most patients in Western countries who develop cholangiocarcinoma do not have Clonorchis infection.

Risk factors

Eating raw or undercooked freshwater fish from countries where infection is common is the key risk factor for Clonorchis infection. Lightly salted, smoked, or pickled fish can also contain infectious parasites.

At-risk populations

Clonorchis infections occur most often in people living in some places in Asia, especially Korea, China, Taiwan, Japan, Asian Russia, Thailand, Cambodia, Laos, Northern Vietnam, and the Philippines.

Additional people who are at risk include:

• Travelers to parts of Asia where the parasite occurs who consume raw or undercooked fish
• Asian immigrants from areas where the parasite occurs

Causes

People can get Clonorchis infection when they eat raw or undercooked freshwater fish that contains the larvae. Freshwater snails can eat the eggs of Clonorchis and become infected, releasing microscopic larvae that then enter freshwater fish. When humans eat raw or undercooked fish with the larvae, these larvae grow into adult flukes. These flukes then live inside the human bile duct system of the liver. The life cycle takes three months to complete in humans. People who are infected can pass eggs in their stool (poop) or may cough them up.

Prevention

To avoid Clonorchis infection, do not eat raw or undercooked freshwater fish from countries where the disease occurs. Lightly salted, smoked, or pickled fish can also contain infectious parasites.

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

Cooking

• Cook fish to an appropriate level (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.

Diagnosis

Talk to a healthcare provider if you traveled to a country where there are Clonorchis parasites.

Stool specimen (sample)

• A trained healthcare provider can use a microscope to identify Clonorchis eggs in stool (poop) specimens.
• A healthcare provider may need more than one stool sample to identify the eggs.
• Note: Stool examination is not likely useful for people whose only exposure to Clonorchis parasites was about three decades ago or longer.

Ultrasound, CT, or MRI

• At times, findings on ultrasound, CT, or MRI associated with Clonorchis infection can help make the diagnosis.

Blood test

• A blood test for detecting Clonorchis infection is available in the US, but it cannot tell the difference between a past or current infection.

Treatment

If your stool specimen is positive for Clonorchis infection, a healthcare provider will treat you with Praziquantel (the treatment of choice) or albendazole (an alternative drug).

Similar diseases

Clonorchis eggs are very similar to Opisthorchis (another liver fluke) eggs. Microscopy can tell the difference between the two.