Clonorchis sinensis
Encyclopedia
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.
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.
Parafossarulus manchouricus
- synonym: Parafossarulus striatulus, often serves as a first intermediate host
for Clonorchis sinensis in China, Japan, Korea and Russia.
Other snail hosts include:
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.
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.
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.
and sometimes even cholangiocarcinoma
, the incidence of which is raised in fluke-infested areas.
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.
, bithionol
, albendazole
and mebendazole
.
Trematoda
Trematoda is a class within the phylum Platyhelminthes that contains two groups of parasitic flatworms, commonly referred to as "flukes".-Taxonomy and biodiversity:...
, Phylum Platyhelminthes. This parasite lives in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
of humans, and is found mainly in the common bile duct
Bile duct
A bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...
and gall bladder, feeding on bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
. These animals, which are believed to be the third most prevalent worm parasite in the world, are endemic to Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, and Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, currently infecting an estimated 30,000,000 humans.
Life cycle
Liver fluke
Liver flukes are a polyphyletic group of trematodes .Adults of liver flukes are localized in the liver of various mammals, including humans. These flatworms can occur in bile ducts, gallbladder, and liver parenchyma. They feed on blood...
), which contains the miracidium that develops into the adult form, floats in freshwater until it is eaten by a snail.
First intermediate host
Freshwater snailFreshwater snail
A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....
Parafossarulus manchouricus
Parafossarulus manchouricus
Parafossarulus manchouricus is a species of freshwater snail with gills and an operculum, an aquatic prosobranch gastropod mollusk in the family Bithyniidae.It is medically important as host for Clonorchis sinensis in East Asia....
- synonym: Parafossarulus striatulus, often serves as a first intermediate host
Intermediate host
A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...
for Clonorchis sinensis in China, Japan, Korea and Russia.
Other snail hosts include:
- Bithynia longicornis - synonym: Alocinma longicornis - in China
- Bithynia fuchsiana - in China
- Bithynia misella - in China
- Parafossarulus anomalosiralis - in China
- Melanoides tuberculata - in China
- Semisulcospira libertina - in China
- Assiminea lutea - in China
- Tarebia graniferaTarebia graniferaTarebia granifera, common name in the aquarium industry the quilted melania, is a species of freshwater snail with an operculum, an aquatic gastropod mollusk in the family Thiaridae...
- in Taiwan, China
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
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
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 intestineSmall intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
unharmed. Reaching the small intestines, the metacercaria navigate toward the human liver, which becomes its final habitat. Clonorchis feed on human bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
created by the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
. In the human liver, the mature Clonorchis reaches its stage of sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
. The hermaphroditic adults produce eggs every 1–30 seconds, resulting in the rapid multiplication of inhabitants in the liver.
Effects on human health
Dwelling in the bile ducts, Clonorchis induces an inflammatory reaction, epithelial hyperplasiaHyperplasia
Hyperplasia means increase in number of cells/proliferation of cells. It may result in the gross enlargement of an organ and the term is sometimes mixed with benign neoplasia/ benign tumor....
and sometimes even cholangiocarcinoma
Cholangiocarcinoma
Cholangiocarcinoma is a cancer of the bile ducts which drain bile from the liver into the small intestine. Other biliary tract cancers include pancreatic cancer, gallbladder cancer, and cancer of the ampulla of Vater...
, the incidence of which is raised in fluke-infested areas.
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
Bile duct
A bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...
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.
Treatment
Drugs used to treat infestation include triclabendazole, praziquantelPraziquantel
Praziquantel is an anthelmintic effective against flatworms. Praziquantel is not licensed for use in humans in the UK; it is, however, available as a veterinary anthelmintic, and is available for use in humans on a named-patient basis....
, bithionol
Bithionol
Bithionol is an anthelmintic used to treat Fasciola hepatica ....
, albendazole
Albendazole
Albendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
and mebendazole
Mebendazole
Mebendazole or MBZ is a benzimidazole drug developed by Janssen Pharmaceutica and marketed as Vermox, Ovex, Antiox, and Pripsen...
.
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 MedicineNew England Journal of MedicineThe New England Journal of Medicine is an English-language peer-reviewed medical journal published by the Massachusetts Medical Society. It describes itself as the oldest continuously published medical journal in the world.-History:...
, April 17, 2008 http://content.nejm.org/cgi/content/full/358/16/e18