Opisthorchis viverrini, a food borne which affects nearly forty million people worldwide. There are three species of liver flukes Opisthorchis viverrini, O. felineus and Clonorchis sinensis. Out of the three types, O. viverrini is categorized as a type 1 carcinogen because it plays a role as the initiator of chronic inflammation and in the development of cholangiocinoma, a fatal disease. There is a great correlation between geographical area, and prevalence of the liver fluke. In a special study using multilocus enzyme electrophoresis, it was found that the liver fluke O. viverrini in people residing in Thailand was different than that of people living in the Democratic Republic of Laos. The conclusion of this study was that there is at least more two different species of O. viverrini. This experiment also showed the separation of the different populations of snails which are usually the first intermediate hosts of the liver fluke parasites. Furthermore, these snails played crucial roles in creating these two-distinct species. Later, five more different species of O. viverrini were found in a different river and wetland ecosystem. To combat these different species, different variations of medications might be needed.
Life cycle of the Opisthorchis viverrini
Opisthorchis viverrini is most prevalent in Thailand, Laos PDR, Cambodia, and Vietnam. There are about nine million people infected in Thailand (Sithithaworn and Haswell-Elkins, 2003). The parasite has a three-host life cycle, with its intermediate host being the snails of abiut three subspecies, Bithynia siamensis siamensis, B. siamensis goniomphalos and B. funiculate (see Kaewkes, 2003). About eighteen species of cyprinid fish which can act with the second intermediate host, along with carnivores like cats and dogs, but the usually humans. We can become infected if we consume a second intermediate host. Humans would most likely contract the parasite by consuming raw or partially cooked cyprinid fish that contained metacercariae. Usually the parasite causes hepatobiliary disease, most of the time cholangiocarcinoma develops ( IARC, 1994; Sithithaworn et al., 1994 ; Honjo et al., 2005).