Fasciola hepatica (sheep liver fluke) occurs worldwide in regions with intense sheep farming, particularly in South America, Africa, China and Australia and also in some areas of Europe.
Humans are incidental hosts; the number of individuals affected is about 2.4 million.
Fasciola gigantica, which resembles Fasciola hepatica, causes infections in Africa and Southeast Asia.
In other countries, isolated infections may be encountered in individuals originating from endemic regions.
Humans become infected by ingesting contaminated water plants which harbour pathogen eggs.
In the acute phase, as the larvae migrate through the liver tissue into the bile ducts, the patient may develop fever, painful hepatomegaly, abdominal pain, skin reactions and eosinophilia. The symptoms usually disappear as the infection becomes chronic.
Mature flukes may occasionally cause symptomatic biliary duct obstruction which may lead to hepatic damage.
Imaging studies may reveal typical changes.
Diagnosis is based on detection of flukes in the biliary ducts or demonstration of eggs in the faeces, bile or biopsy specimen. Antibody assays can also be used.
The drug of choice is triclabendazole (special license may be required).
Clonorchis sinensis and Opistorchis sp.
Clonorchis sinensis (Chinese liver fluke) is a trematode (fluke), which mainly occurs in China, Korea and Southeast Asia.
About 28 million individuals are estimated to be infected.
Opistorchis parasites are rarer liver flukes, and they are encountered in Southeast Asia and Russia.
In other countries, isolated infections may be encountered in individuals originating from endemic regions.
Humans are infected by eating raw or partially cooked small fresh water fish.
Time from infection to oviposition is about one month. One fluke may live up to 20 years and continue to produce eggs.
Clonorchis infection is usually asymptomatic.
A heavy worm burden in the biliary ducts may lead to cholangitis, periductal fibrosis, biliary tract obstruction and associated hepatic damage. Chronic infection is associated with an increased risk of cholangiocarcinoma.
Diagnosis is made after demonstration of eggs in the faeces or bile. In rare cases, flukes themselves may be detected in a surgically obtained sample of the bile ducts.
Praziquantel(may require special license) is the drug of choice, with albendazole (may require special license) as the secondary alternative.
References
Ashrafi K, Bargues MD, O'Neill S et al. Fascioliasis: a worldwide parasitic disease of importance in travel medicine. Travel Med Infect Dis 2014;12(6 Pt A):636-49. [PubMed]
Keiser J, Utzinger J. Emerging foodborne trematodiasis. Emerg Infect Dis 2005;11(10):1507-14. [PubMed]