Clonorchis sinensis
The Clonorchis sinensis is a human liver fluke in the class Trematoda, Phylum Platyhelminthes. This parasite lives in the liver of humans, and is found mainly in the common bile duct and gall bladder, feeding on bile. These animals, which are believed to be the third most prevalent worm parasite in the world, are endemic to Japan, China, Taiwan, and Southeast Asia, currently infecting an estimanted 30,000,000 humans.
The adult clonorchis, which is about 10-25 mm long and 3-5 mm wide, is hermaphroditic. Their life cycle begins first in a host's feces as an egg containing miracidia. The next host is a snail, where the miracidium hatches out of the egg, after it is ingested. In the snail, the miracidium develops into a sporocyst which then internally, develops rediae. The rediae, still developing inside of the snail, become larger, and begin to produce cercariae. The individual cercaria exit from the snail and penetrate the skin of a freshwater fish and then into their muscle and become metacercarial cysts. The metacercariae can then be ingested by humans who eat undercooked or raw fish, who in turn become infected at the same time. These metacercariae enter the small intestine and migrate into, and mature in the human liver, inside of the common bile duct and gall bladder. The mature liver flukes lay eggs after about 3-4 weeks. The fully developed eggs are then passed in the feces, where the life cycle can begin again.
References
- Freeman, Scott (2002). Biological Science. Upper Saddle River, Prentice Hall Inc.
- Gilbertson, Lance (1999). Zoology Laboratory Manual fourth edition. New York, The McGraw-Hill Companies, Inc.
