Clonorchis sinensis is a parasitic worm native to Asia. It is sometimes referred to by the common name “Oriental liver fluke.” It is one of the most common causes of parasitic infection around the world, and affects residents and visitors in regions like China, Taiwan, Southeast Asia, and Japan. When infection with this parasite is identified by a doctor, it can be treated with antiparasitic drugs which will kill the worms and halt their life cycle in the body.
The Clonorchis sinensis life cycle starts with a free-floating egg in freshwater. The egg is consumed by a snail and once inside the snail it hatches and matures. The fluke then burrows out of the snail and into the water, where it can seek out a new host. Freshwater fishes are preferred hosts for the parasites, which burrow into the body before encapsulating themselves. This capsule is a critical part of the fluke's survival strategy.
When infected fish are eaten by humans, if the fish are not fully cooked, the flukes survive intact. Normally the stomach juices would kill the Clonorchis sinensis, but because of the capsule, the parasites are able to survive until they reach the intestine. From there, they enter the bile ducts of the liver and begin producing eggs. People shed the eggs in their feces, and some of the eggs work their way into the water supply to start the cycle all over again.
People infected with Clonorchis sinensis flukes experience symptoms like jaundice, fever, chills, and stomach pains. Some people develop complications such as digestive problems and bile obstruction. A doctor can diagnose Clonorchis sinensis infection with the assistance of a stool sample in which the eggs can be identified. Because the eggs of several parasites look similar, a doctor may also request a tissue sample to identify adult flukes in the liver.
The risk of Clonorchis sinensis infection can be greatly reduced by making sure that all freshwater fish are thoroughly cooked. Numerous other parasites inhabit fish found in freshwater and even in areas where Clonorchis sinensis is rare, it is still a good idea to cook fish all the way through. Saltwater fish are less prone to parasitic infection, and fans of Asian cuisine may note that dishes made with raw or rare fish are made with saltwater fish species. It is also advisable to observe other hygiene precautions including washing hands and utensils thoroughly after handling raw fish.