- Infection of the biliary passages with Clonorchis sinensis, also called Opisthorchis sinensis.
- It may lead to inflammation of the biliary tract, proliferation of biliary epithelium, progressive portal fibrosis, and sometimes bile duct carcinoma.
- Extension to the liver may lead to fatty changes and cirrhosis.
- Found across parts of Asia, Clonorchis is also known as the Chinese or oriental liver fluke.
- Liver flukes infect the liver, gallbladder, and bile duct in humans.
- While most infected persons do not show any symptoms, infections that last a long time can result in severe symptoms and serious illness.
- Untreated, infections may persist for up to 25–30 years, the lifespan of the parasite.
- Diagnosis of Clonorchis infection is based on microscopic identification of the parasite’s eggs in stool specimens.
- Safe and effective medication is available to treat Clonorchis infections.
- Adequately freezing or cooking fish will kill the parasite.
Epidemiology & Risk Factors
Clonorchis species are liver fluke parasites (trematodes or worms) such as fasciola hepatica.
Liver fluke infections occur mostly in people living in some areas where the parasites are found. Clonorchis is found mainly in Korea, China, Taiwan, Northern Vietnam, Japan, and Asian Russia. Travelers to Asia who consume raw or undercooked fish are at risk for liver fluke infection. People become infected by eating raw or undercooked freshwater fish containing the larvae. Lightly salted, smoked, or pickled fish may contain infectious parasites. Drinking river water or other non-potable water will not lead to infection with Clonorchis.
- The trematode Clonorchis sinensis (Chinese or oriental liver fluke) is an important foodborne pathogen and cause of liver disease in Asia.
- This appears to be the only species in the genus involved in human infection.
- Clonorchis sinensis eggs are discharged in the biliary ducts and in the stool in an embryonated state.
- Eggs are ingested by a suitable snail intermediate host
- Eggs release miracidia image , which go through several developmental stages
- The cercariae are released from the snail and, after a short period of free-swimming time in water, they come in contact and penetrate the flesh of freshwater fish, where they encyst as metacercariae
- Infection of humans occurs by ingestion of undercooked, salted, pickled, or smoked freshwater fish
- After ingestion, the metacercariae excyst in the duodenum image and ascend the biliary tract through the ampulla of Vater
- Maturation takes approximately one month.
- The adult flukes (measuring 10 to 25 mm by 3 to 5 mm) reside in small and medium sized biliary ducts.
Prevention & Control
- Do not eat raw or undercooked freshwater fish. Lightly salted, smoked, or pickled fish can contain infectious parasites. Drinking river water or other non-potable water will not lead to infection with Clonorchis.
The FDA recommends the following for fish preparation or storage to kill any parasites.
- Cook fish adequately (to an internal temperature of at least 145° F [~63° C]).
- Freezing (Fish)
- 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 at 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.