Fascioliasis is a parasitic infection typically caused by Fasciola hepatica, which is also known as "the common liver fluke" or "the sheep liver fluke." A related parasite, Fasciola gigantica, also can infect people. Fascioliasis is found in all 5 continents, in over 50 countries, especially where sheep or cattle are reared. People usually become infected by eating raw watercress or other water plants contaminated with immature parasite larvae. The immature larval flukes migrate through the intestinal wall, the abdominal cavity, and the liver tissue, into the bile ducts, where they develop into mature adult flukes, which produce eggs. The pathology typically is most pronounced in the bile ducts and liver. Fasciola infection is both treatable and preventable.
Left: Fasciola hepatica egg in an unstained wet mount (400x magnification). F. hepatica eggs are broadly ellipsoidal, operculated, and measure 130-150 μm by 60-90 µm. Center: Adult Fasciola hepatica fluke stained with carmine (30 mm by 13 mm). Right: Fossaria bulamoides, a snail host for F. hepatica in the western United States. Credit: DPDx, Conchology, Inc, Mactan Island, Philippines.