Clonorchis

Clonorchis sinensis
An adult Clonorchis sinensis has these main body parts: oral sucker, pharynx, caecum, ventral sucker, vitellaria, uterus, ovary, Mehlis' gland, testes, excretory bladder. (H&E stain)
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 belonging to 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. 85% of cases are found in China. The infection called clonorchiasis generally appears as jaundice, indigestion, biliary inflammation, bile duct obstruction, even liver cirrhosis, cholangiocarcinoma (CCA), and .

It is the most prevalent human trematode in Asia, and is still transmitted in Korea, China, Vietnam and also Russia, with 200 million people at constant risk. Recent studies have proved that it is definite cancer-causing agent in the liver (carcinoma) and bile duct (CCA). For this reason the International Agency for Research on Cancer has classed it as a group 1 biological carcinogen in 2009.

The symptoms of C. sinensis infection (clonorchiasis) have been known from ancient times in China. The earliest record is from corpses buried in 278 BCE at Jiangling County of Hubei Province and the Warring States tomb of the western Han Dynasty. But the parasite was discovered only in 1874 by James McConnell, a professor of pathology and resident physician at the Medical College Hospital in Calcutta. He recovered the fluke from a twenty-year-old Chinese carpenter who died on 8 September 1874. On autopsy, he observed that the corpse had swollen liver (hepatomegaly) and distended bile ducts, which he noted were blocked by "small, dark, vermicular-looking bodies." He recovered the vermicules (worms) and compared them with known flukes Fasciola hepatica and Distoma lanceolatum. He concluded that the new fluke was significantly different. He published his observations in the 21 August 1875 issue of The Lancet. The formal scientific description was published by Thomas Spencer Cobbold in 1875. Cobbold named it Distoma sinense. But in 1876, Rudolf Leuckart named it as Distomum spithulatum. Kenso Ishisaka recorded the first case of clonorchiasis in Japan in 1877. McConnell identified another infection in a Chinese cook from Hong Kong in 1878. Erwin von Baelz reported the presence of similar flukes from an autopsy of a Japanese patient at Tokyo University in 1883. He recorded two different forms, naming the smaller, more pathogenic form as Distoma hepatis endemicum sive perniciosum, and the larger, less pathogenic form as D.h.e.s. innocuum. Isao Ijima correctly redescribed them as the same species, but still wrongly renamed it Distoma endemicum in 1886. When a new genus Opisthorchis was created by Émile Blanchard in 1895, Cobbold's species name D. sinense was moved to the new genus because of close similarities with the other members. But further analyses by Arthur Looss showed significant differences from the general features of Opisthorchis, particularly on the highly branched testes. He created a new genus Clonorchis (from Greek Klon meaning "twig/branch", orkhis meaning "testis") in 1907. But similar to Baelz, he differentiated the larger species as Clonorchis sinensis, which are mostly found in China, and the smaller species as C. endemicum, found mostly in Japan. In 1912, Harujiro Kobayashi corrected the classification that the differences in sizes were due to the nature of the host and intensity of infection, and had nothing to do with the biology. Hence, he supported only C. sinensis. Kobayashi was also the first to discover fish as the second intermediate host in 1911. Masatomo Muto discovered snails as the first intermediate host in 1918.

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