Clonorchis sinensis, the Chinese or oriental liver fluke, is an important human parasite and is widely distributed in southern Korea, China (including Taiwan), Japan, northern Vietnam and the far eastern part of Russia. Clonorchiasis occurs in all parts of the world where there are Asian immigrants from endemic areas. The human and animal reservoir hosts (dogs, pigs, cats and rats) acquire the infection from the ingestion of raw fish containing infectious metacercariae. The first intermediate snail hosts are mainly species of Parafossarulus and Bithynia. Numerous species of freshwater fish serve as the second intermediate hosts of C. sinensis. Extensive studies of clonorchiasis during several decades in Japan, Korea, China and other countries have shown much progress in proving its morphological features including ultrastructure, biology, pathogenesis, epidemiology, clinical manifestations and chemotherapy. The present review deals with mainly current results obtained on the epidemiological, pathological and clinical aspects, as well as control measures in endemic areas. As for the complications of clonorchiasis, formation of calculi in the intrahepatic biliary passages is one of the most characteristic pathological features. It is sometimes accompanied by suppurative cholangitis, cholecystitis, cholangiohepatitis and ultimately can cause cholangiocarcinoma. Experimental results on the relationship to the occurrence of cholangiocarcinoma are presented. Clinical diagnosis by radiological findings including cholangiography, sonography and computerized tomography as well as magnetic resonance imaging for biliary or pancreatic ducts are outlined. Current studies on immunology and molecular biology of C. sinensis were introduced. Praziquantel is the drug of choice for clonorchiasis. The most effective regimen is 25 mg kg(-1) three times daily (total dose, 75 mg kg(-1)) administered orally at 5- to 6-h intervals over a single day. Prevention and control measures are also discussed.

Among taeniid tapeworms infecting humans through pork or beef, Taenia solium Linnaeus 1758 and Taenia saginata Goeze 1782 have already been known. Based on the morphologic characteristics of adult and metacestodes of Asian Taenia saginata, the third kind of human taeniid tapeworm known to distribute in Asian countries, a new species name of Taenia asiatica is proposed. In addition to the known biology in their intermediate hosts, T. asiatica was different morphologically from Taenia saginata Goeze 1782 in having the unarmed rostellum on the scolex of adult, the large number of 'uterine twigs' and the existence of 'posterior protuberance'. These structures in the gravid proglottids were used as taxonomic keys in taeniid tapeworms for the first time. T. asiatica metacestode (Cysticercus viscerotropica) was different morphologically from T. saginata metacestode (Cysticercus bovis) in having wartlike formations on the external surface of the bladder wall.

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Chronic Clonorchis sinensis (CS) infection is etiologically related to cholangiocarcinoma (CHCA) in human and animals. This study was carried out to clarify the role of CS infection on dimethylnitrosamine (DMN)-induced cholangiocarcinogenesis. Fifteen hamsters were administered with 15 ppm DMN for 4 weeks and one week later, the hamsters were infected with 15 metacercariae of CS (DMN-->CS group). The other 15 hamsters were infected with CS and after 5 weeks they were treated with the drug, praziquantel. Again one week later, the hamsters were administered with DMN (CS-->DMN group). The other 15 hamsters were administered with DMN and CS simultaneously (CS+DMN group). Histopathological examination of the livers showed CHCA with papillary or adenomatous hyperplasia of bile ductules in 3 of 15 hamsters of DMN-->CS group and in 11 of 15 hamsters of DMN+CS group. These results suggest that CS infection to hamsters may have a promoting effect on the development of CHCA.

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