page_title: Opisthorchis viverrini
section_title: Lifecycle
hierarchical_section_title: Opisthorchis viverrini / Lifecycle
caption_attribution_description: Opisthorchiasis [Opisthorchis felineus] [Opisthorchis viverrini] Causal Agent: Trematodes (flukes) Opisthorchis viverrini (Southeast Asian liver fluke) and O. felineus (cat liver fluke). Life cycle of Opistorchis spp. The adult flukes deposit fully developed eggs that are passed in the feces . After ingestion by a suitable snail (first intermediate host) , the eggs release miracidia , which undergo in the snail several developmental stages (sporocysts , rediae , cercariae ). Cercariae are released from the snail and penetrate freshwater fish (second intermediate host), encysting as metacercariae in the muscles or under the scales . The mammalian definitive host (cats, dogs, and various fish-eating mammals including humans) become infected by ingesting undercooked fish containing metacercariae. After ingestion, the metacercariae excyst in the duodenum and ascend through the ampulla of Vater into the biliary ducts, where they attach and develop into adults, which lay eggs after 3 to 4 weeks . The adult flukes (O. viverrini: 5 mm to 10 mm by 1 mm to 2 mm; O. felineus: 7 mm to 12 mm by 2 mm to 3 mm) reside in the biliary and pancreatic ducts of the mammalian host, where they attach to the mucosa. Geographic Distribution: O. viverrini is found mainly in northeast Thailand, Laos, and Kampuchea. O. felineus is found mainly in Europe and Asia, including the former Soviet Union.
context_page_description: 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 by M.J. Poirier in 1886. The first human case was discovered by Robert Thomson Leiper in 1915.
  O. viverrini 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.
context_section_description: O. viverrini is a hermaphroditic liver fluke. Similar to C. sinensis and O. felineus, it requires three different hosts to complete its lifecycle. Freshwater snails are the first intermediate hosts in which asexual reproduction takes place, and freshwater fishes belonging to the family Cyprinidae) are second intermediate hosts in which larval development occurs. Fish–eating (piscivorous) mammals, including humans, dogs, and cats, act as definitive hosts, in which sexual reproduction occurs.  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.
caption: Lifecycle of Opisthorchis