Clonorchis sinensis

Clonorchis sinensis
Clonorchis sinensis under a light microscope. Notice the ovaries. This species is monoecious,
Scientific classification
Kingdom:	Animalia
Phylum:	Platyhelminthes
Class:	Trematoda
Order:	Opisthorchiida
Family:	Opisthorchiidae
Genus:	Clonorchis
Species:	C. sinensis
Binomial name
Clonorchis sinensis Looss, 1907

Clonorchis sinensis, the Chinese liver fluke, 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 estimated 30,000,000 humans.

Life cycle

An adult Clonorchis sinensis has these main body parts: oral sucker, pharynx, caecum, ventral sucker, vitellaria, uterus, ovary, Mehlis' gland, testes, exretory bladder.

Life cycle of Clonorchis sinensis

The egg of a Clonorchis sinensis (commonly: human liver fluke), which contains the miracidium that develops into the adult form, floats in freshwater until it is eaten by a snail.

First intermediate host

Freshwater snail Parafossarulus manchouricus - synonym: Parafossarulus striatulus, often serves as a first intermediate host for Clonorchis sinensis in China, Japan, Korea and Russia.^[1][2]

Other snail hosts include:

• Bithynia longicornis - synonym: Alocinma longicornis - in China^[2]
• Bithynia fuchsiana - in China^[2]
• Bithynia misella - in China^[2]
• Parafossarulus anomalosiralis - in China^[2]
• Melanoides tuberculata - in China^[2]
• Semisulcospira libertina - in China^[2]
• Assiminea lutea - in China^[2]
• Tarebia granifera - in Taiwan, China^[2]

Once inside of the snail body, the miracidium hatches from the egg, and parasitically grows inside of the snail. The miracidium develops into a sporocyst, which in turn house the asexual reproduction of redia, the next stage. The redia themselves house the asexual reproduction of free-swimming cercaria. This system of asexual reproduction allows for an exponential multiplication of cercaria individuals from one miracidium. This aids the Clonorchis in reproduction, because it enables the miracidium to capitalize on one chance occasion of passively being eaten by a snail before the egg dies.

Once the redia mature, having grown inside the snail body until this point, they actively bore out of the snail body into the freshwater environment.

Second intermediate host

There, instead of waiting to be consumed by a host (as is the case in their egg stage), they seek out a fish. Boring their way into the fish's body, they again become parasites of their new hosts.

Once inside of the fish muscle, the cercaria create a protective metacercarial cyst with which to encapsulate their bodies. This protective cyst proves useful when the fish muscle is consumed by a human.

Definitive host

The acid-resistant cyst enables the metacercaria to avoid being digested by the human gastric acids, and allows the metacercaria to reach the small intestine unharmed. Reaching the small intestines, the metacercaria navigate toward the human liver, which becomes its final habitat. Clonorchis feed on human bile created by the liver. In the human liver, the mature Clonorchis reaches its stage of sexual reproduction. The hermaphroditic adults produce eggs every 1–30 seconds, resulting in the rapid multiplication of inhabitants in the liver.

Effects on human health

Main article: Clonorchiasis

Dwelling in the bile ducts, Clonorchis induces an inflammatory reaction, epithelial hyperplasia and sometimes even cholangiocarcinoma, the incidence of which is raised in fluke-infested areas.^[3]

One adverse effect of Clonorchis is the possibility for the adult metacercaria to consume all bile created in the liver, which would inhibit the host human from digesting, especially fats. Another possibility is obstruction of the bile duct by the parasite or its eggs, leading to biliary obstruction and cholangitis (specifically oriental cholangitis).

Central Serous Retinopathy (CSR) a report of 80 cases by Dr. John Chiao-nan Chang, M.D. and Dr. Yin-Ping Wang, M.D. Hong Kong on page 125 of their report observed that 19% of the cases of CSR in their sample tested positive for Clonorchis sinensis.^[4]

Treatment

Drugs used to treat infestation include triclabendazole, praziquantel, bithionol, albendazole and mebendazole.^{[citation needed]}

See also

• List of parasites (human)

References

1. ^ Clonorchis sinensis. Web Atlas of Medical Pathology, accessed 1 April 2009
2. ^ ^{a b c d e f g h i} World Health Organization (1995). Control of Foodborne Trematode Infection. WHO Technical Report Series. 849. PDF part 1, PDF part 2. page 125-126.
3. ^ Kumar et al.: Robbins & Cotran Pathologic Basis of Disease 7E
4. ^ Report Text

External links

• 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.
• Video of Clonorchis sinensis infestation in the Images in Clinical Medicine section of the New England Journal of Medicine, April 17, 2008 [1]