Opisthorchis viverrini

Opisthorchis viverrini, common name Southeast Asian liver fluke, is a food-borne trematode parasite from the family Opisthorchiidae that infects the bile duct. People are infected after eating raw or undercooked fish. Infection with the parasite is called opisthorchiasis. O. viverrini infection also increases the risk of cholangiocarcinoma, a cancer of the bile ducts.

A small, leaf-like fluke, O. viverrini completes its lifecycle in three different animals. Snails of the species Bithynia are the first intermediate hosts, fish belonging to the family Cyprinidae are the second intermediate host, and the definitive hosts are humans and other mammals such as dogs, cats, rats, and pigs. It was first discovered in the Indian fishing cat (Prionailurus viverrus) by M.J. Poirier in 1886. The first human case was discovered by Robert Thomson Leiper in 1915.

O. viverrini (together with Clonorchis sinensis and Opisthorchis felineus) is one of the three most medically important species in the family Opisthorchiidae. In fact O. viverrini and C. sinensis are capable of causing cancer in humans, and are classified by the International Agency for Research on Cancer as a group 1 biological carcinogen in 2009. O. viverrini is found in Thailand, the Laos, Vietnam, and Cambodia. It is most widely distributed in northern Thailand, with high prevalence in humans, while central Thailand has a low rate of prevalence.