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Liver flukes: Fascioliasis

Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
Peter F Weller, MD, MACP
Section Editor
Edward T Ryan, MD, DTMH
Deputy Editor
Elinor L Baron, MD, DTMH


Fascioliasis is a trematode flatworm infection caused by Fasciola hepatica or Fasciola gigantica [1]. F. hepatica has a worldwide distribution; F. gigantica occurs predominantly in the tropics. Both parasites are hermaphroditic, have similar life cycles, and cause similar clinical manifestations in humans. The organism causes "liver rot" among sheep and cattle, which are the definitive hosts; humans are incidental hosts.


Epidemiology — F. hepatica occurs globally, mainly in sheep-rearing areas of temperate climates. Infection is endemic in Central and South America (especially Bolivia and Peru), Europe (especially Portugal, France, Spain, and Turkey), Asia (especially China, Vietnam, Taiwan, Korea, and Thailand), Africa, and the Middle East [2]. Sporadic cases have also been reported in the United States [3], Australia [4], and elsewhere [1]. An estimated 2.4 to 17 million people are infected in more than 51 countries [5]; 91 million are at risk worldwide [6].

Sheep and cattle are the most important definitive hosts of F. hepatica; goats, buffalo, horses, camels, hogs, deer, and rabbits can also be infected. Snails are intermediate hosts. Humans are incidental hosts and most often acquire infection by eating watercress grown in sheep-raising areas. Infection may also be transmitted by other freshwater plants, including water lettuce, mint, alfalfa, and parsley. Humans can also acquire infection by drinking contaminated water containing viable metacercariae [7]; outbreaks have been described [8]. The incidence of animal and human infection rises during wet years because of an increased number of snails and longer survival of encysted cercariae [9].

In some areas, endemicity is almost 100 percent. In endemic regions, very young children and women are most likely to be infected. There is a high incidence of coinfection with other parasites, especially echinococcosis.

Life cycle — The life cycle of fascioliasis begins with release of un-embryonated eggs into the biliary ducts, which are then passed in the stool of herbivores (definitive hosts) or humans (incidental hosts) (figure 1). Eggs become embryonated in water and release miracidia, which invade a snail (intermediate host), where the parasites undergo several developmental stages (sporocysts, rediae, and cercariae). The cercariae are released and encyst as metacercariae on aquatic vegetation.

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Literature review current through: Nov 2017. | This topic last updated: Feb 15, 2017.
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