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Synonyms: Opisthorchis sinensis = Clonorchis sinensis or Chinese or oriental liver fluke, Opisthorchis felineus = Opisthorchis tenuicollis or cat liver fluke, Opisthorchis viverrini = Southeast Asian liver fluke
Opisthorchiasis is a trematode (fluke) infection caused by infection with one of the species of the liver fluke Opisthorchis, which is acquired by eating raw or undercooked freshwater fish containing infectious metacercariae. The three species are: O. sinensis (still widely known as Clonorchis sinensis), O. felineus/tenuicollis and O. viverrini.
Opisthorchis spp. have a complex life cycle involving a definitive mammalian host and two intermediate aquatic hosts.
- Humans or other mammals eat the encysted metacercariae in inadequately cooked/raw/pickled fish.
- After digestion of the cyst in the duodenum, the larva enters the biliary duct where it matures into the adult worm, which lives off mucosal secretions.
- The worm lays eggs which pass into the stool and enter freshwater where they form a miracidium either before or after colonising various species of aquatic snail.
- Asexual reproduction leads to the formation of metacercariae. These pass to fish where they become encysted in the muscles/scales and complete their life cycle by being eaten by humans/other mammals.
Approximately 35 million people are infected by liver flukes.
- O. (Clonorchis) sinensis:
- This organism is endemic in Southeast Asia, Japan, Korea, Taiwan and most of China.
- There are an estimated 19 million cases of human infestation.
- It is relatively small (10-25 mm x 3 mm).
- It infects humans, dogs, pigs, cats, rats and a variety of wild animals.
- O. felineus/tenuicollis:
- This is normally an intestinal parasite of cats, dogs, foxes, pigs and cetaceans (whales/porpoises/dolphins) in Eastern Europe, Siberia and other parts of Asia.
- It is morphologically very similar to O. sinensis.
- There are an estimated 1.2 million cases worldwide.
- O. viverrini:
- Found in domesticated and wild dogs and cats in Southeast Asia.
- It is a very common human infection in North East Thailand where it is said to infect up to half of the population. Worldwide it is estimated at 9 million cases.
- It is morphologically very similar to O. sinensis/O. felineus.
- Most infections are asymptomatic.
- Mild infections may cause dyspepsia, abdominal pain, diarrhoea or constipation.
- Longer-term infections may cause more severe symptoms and may lead to hepatomegaly and malnutrition.
- Cholangitis, cholecystitis, and cholangiocarcinoma may develop but only rarely.
- Infections due to O. felineus may also present an acute phase similar to Katayama fever (schistosomiasis), with fever, facial oedema, lymphadenopathy, arthralgias, rash and eosinophilia. Chronic O. felineus infection may also involve the pancreatic ducts.
- Viral hepatitis.
- Inflammatory bowel disease.
- Primary biliary cirrhosis.
- Carcinoma of head of pancreas.
- Microscopic stool examination may reveal the eggs.
- Duodenal aspiration is more sensitive for this purpose than examination of two stool specimens.
- An enzyme-linked immunosorbant assay (ELISA) method for detecting antigen in the stool may be used to diagnose opisthorchiasis. Polymerase chain reaction techniques are being developed to improve diagnosis.[4, 5]
- FBC may reveal anaemia and eosinophilia.
- Praziquantel is the treatment of choice. Albendazole is an alternative.
- Intercurrent bacterial infections are treated with appropriate antibiotics.
- Surgery may be needed to treat biliary tract complications.
- Intercurrent bacterial infection
- Pyogenic cholangitis
- Early, moderate infestations are likely to be cured without complications.
- Chronic or severe infestations tend to lead to complications, and death is not uncommon.
- Proper cooking of fish..
- Freezing fish intended for raw consumption.
- Use of molluscicides is the most frequent public health intervention, as it prevents the transmission of many other trematodes, including Schistosoma spp.
- Treatment of animals to reduce the reservoir and stock losses has been used.
- Prophylactic use of praziquantel.
Further reading and references
Opisthorchis Infection; DPDx, Centers for Disease Control and Prevention
Lim JH; Liver flukes: the malady neglected. Korean J Radiol. 2011 May-Jun12(3):269-79. doi: 10.3348/kjr.2011.12.3.269. Epub 2011 Apr 25.
Melling N, Hohenberger W, Yedibela S; Opisthorchiasis mimicking primary biliary cirrhosis as an indication for liver J Hepatol. 2009 May50(5):1057-9. Epub 2009 Mar 14.
Umesha KR, Kumar S, Parvathi A, et al; Opisthorchis viverrini: detection by polymerase chain reaction (PCR) in human Exp Parasitol. 2008 Dec120(4):353-6. Epub 2008 Sep 9.
Intapan PM, Thanchomnang T, Lulitanond V, et al; Rapid molecular detection of Opisthorchis viverrini in human fecal samples by Am J Trop Med Hyg. 2009 Nov81(5):917-20.
Opisthorchiasis; World Health Organization