Clonorchis sinensis
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
Order: Opisthorchiida
Family: Opisthorchiidae
Genus: Clonorchis
Species: sinensis
The Clonorchis sinensis is a human liver fluke in the class Trematoda, Phylum Platyhelminthes. These animals, which are believed to be the third most prevalent worm parasite in the world .This parasite lives in the liver of humans, and is found mainly in the common bile duct and gall bladder, feeding on bile. The worm are lanceolate, flat, transparent, pinkish in the living condition and measure 11-20mm by 3-4.5mm . each end of the adult worm is narrower than the midportion of the body. At the anterior tip, there is oral sucker and at about one-fifth(1\5) length posteriorly. There is a smaller ventral sucker called acetabulum, the tequment has n spine. The typical small yellowish-brown C. sinensis egg measures 30 by 15 µm, its equipped with a distinict operculum opposite a small knob. A thick rim is strategically located around the operculum and is referred to as shoulders.
Life cycle
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 often serves as an first intermediate host for Clonorchis sinensis. Other snail hosts include Bithynia, Tarebia, Alocinma and Bulimus.
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. 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. 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. The adults flukes can live for up to 26 years but on average survive for 10 years.
Pathogenesis
as the worms mature in the distal bile ducts, an inflammatory response is seen in the biliary epithelium. The extent of pathological changes is related to the intensity and duration of infection. Lesions are mainly confined to the biliary system and are the result of mechanical irritation and toxic products by the worm.
Light infections are usually asymptomatic. In Heavier infections , there is thickening and localized dilations of the bile ducts with hyperplasia of the mucinous gland. As a result, the biliary tract may become obstructed, causing bile retention, infiltration of lymphocytes and eosinophils and fibrosis.
The infection have been associated with obstructive jaundice, which may be aggravated by biliary stones and liver abscesses. Many patients infected with C. sinensis have recurrent pyogenic cholangitis. Acute pancreatitis , cholecystitis and cholelithiasis may be the results of worm invasion. Jaundice may occur if a mass of flukes obstructs the biliary tree. There was no direct link between infection and carcinoma, although one of the first steps in malignant transformation may be induce by the biliary tract hyperplasia, caused by the worms.
Treatment
Drugs used to treat infestation include triclabendazole, praziquantel, bithionol, albendazole and mebendazole.