Fascioliasis is caused by the trematodes Fasciola hepatica (the sheep liver fluke) and Fasciola gigantica, parasites of herbivores that can infect humans accidentally. In agriculture, Fasciola infections cause billions of dollars of losses due to poor meat quality and loss of milk production and condemnation of livers.
Geographic Distribution
Fascioliasis occurs worldwide. Human infections with F. hepatica are found in areas where sheep and cattle are raised, and where humans consume raw watercress, including Europe, the Middle East, and Asia. Infections with F. gigantica have been reported, more rarely, in Asia, Africa, and Hawaii.
Clinical Features
During the acute phase (caused by the migration of the immature fluke through the hepatic parenchyma), symptoms include abdominal pain, hepatomegaly (enlarged liver), fever, vomiting, diarrhea, urticaria and eosinophilia, and can last for months. In the chronic phase (caused by the adult fluke within the bile ducts), the symptoms are more distinct and reflect intermittent biliary obstruction and inflammation. Occasionally, ectopic locations of infection (such as intestinal wall, lungs, subcutaneous tissue, and pharyngeal mucosa ) can occur.
Laboratory Diagnosis
Microscopic identification of eggs is useful in the chronic (adult) stage for diagnosis. Eggs can be recovered in the stools or in material obtained by duodenal (small intestine) or biliary drainage. They are morphologically indistinguishable from those of the fluke F. buski. False fascioliasis (pseudofascioliasis) refers to the presence of eggs in the stool resulting not from an actual infection but from recent ingestion of infected livers containing eggs. This situation (with its potential for misdiagnosis) can be avoided by having the patient follow a liver-free diet several days before a repeat stool examination. Antibody detection tests are useful especially in the early invasive stages, when the eggs are not yet apparent in the stools, or in ectopic fascioliasis.
Treatment
Unlike infections with other flukes, F. hepatica infections may not respond to Praziquantel. The drug of choice is triclabendazole with bithionol as an alternative.
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