Opisthorchis viverrini, common name Southeast Asian liver fluke, is a food-borne trematode parasite from the family Opisthorchiidae that infects the bile duct.

O. viverrini (together with Clonorchis sinensis and Opisthorchis felineus) is one of the three most medically important species in the family Opisthorchiidae.

[9][10] O. viverrini was first described by a French parasitologist Jules Poirier in 1886, who discovered the parasite in an Indian fishing cat (Prionailurus viverrus), originally from Southeast Asia, that died in the Zoological Gardens attached to the National Museum of Natural History in Paris.

[11][12] American parasitologists Charles Wardell Stiles and Albert Hassall redescribed it and assigned it to the existing genus Opisthorchis (created by a French zoologist Raphaël Blanchard) in 1891.

The first human specimen was described by a British parasitologist Robert Thomson Leiper in 1915, but without knowing the exact parasite.

Leiper received the specimens from an Irish medical doctor, Arthur Francis George Kerr, who had collected them from the post mortem examination of two prisoners at a jail in Chiang Mai, northern Thailand.

[13] C. Prommas also reported O. felineus in 1927 from an autopsy of a 17-year-old Thai male residing in Roi Et, northeast Thailand.

[14] It was in 1955 when Elvio H. Sadun from the U. S. Public Health Service analysed the cases of opisthorchiasis in Thailand and concluded that all the infections were due to O.

The body of an adult O. viverrini is flat (dorsoventrally flattened) like a leaf, shaped like a lancet, and can be seen through (transparent).

Fish–eating (piscivorous) mammals, including humans, dogs, and cats, act as definitive hosts, in which sexual reproduction occurs.

[8] As a result of poor sanitation practices and inadequate sewerage infrastructure, O. viverrini-infected people pass the trematode's eggs in their feces into bodies of fresh water from where snails become infected.

The known hosts include Puntius brevis, P. gonionotus, P. orphoides, P. proctozysron, P. viehoeveri, Hampala dispar, H. macrolepidota, Cyclocheilichthys armatus, C. repasson, Labiobarbus lineatus, Esomus metallicus, Mystacoleucus marginatus, Puntioplites falcifer, Onychostoma elongatum, Osteochilus hasseltii, Hypsibarbus lagleri, and Barbodes gonionotus.

[18] The metacercarial stage is infective to humans and other fish-eating mammals, including dogs, cats,[8] rats, and pigs.

[1] The young adult worm escapes from the metacercarial cyst in the upper small intestine and then migrates through the ampulla of Vater into the biliary tree, where it develops to sexual maturity over 4–6 weeks, thus completing the lifecycle.

[5] O. viverrini remains a major public health problem in the Mekong Basin in Southeast Asia.

[28] It is not highly prevalent in Vietnam, but accurate survey is difficult because it is often co-infected with other flukes such as Haplorchis pumilio, H. taichui, and C. sinensis.

Heavy infection can produce problems in the liver, gall bladder, and bile ducts.

[33] The collective effects in addition to specific parasite secretion and the host's immune reactions account for the development of cholangiocarcinoma.

The infection is not immediately life-threatening; cancer develops after 30–40 years, but death occurs very fast, within 3–6 months of diagnosis.

[4] Infections with O. viverrini and of other liver flukes in Asia affect the poor and poorest people.

[34] There is no approved drug for the infection; however, Swiss researchers have tested tribendimidine and achieved a 70% cure rate.

[37] In addition to praziquantel other commonly used anthelmintics such as albendazole, artesunate, and miltefosine are found to be effective on the cercariae but not on the metacercariae.