About Fasciola

Fascioliasis is an infectious disease caused by Fasciola parasites, which are flat worms referred to as liver flukes. The adult (mature) flukes are found in the bile ducts (the duct system of the liver) of infected people and animals, such as sheep and cattle. In general, fascioliasis is more common in livestock and other animals than in people.

Two Fasciola species (types) infect people. The main species is Fasciola hepatica, which is also known as “the common liver fluke” and “the sheep liver fluke.” A related species, Fasciola gigantica, also can infect people.

Fascioliasis is found in more than 70 countries, especially where sheep or cattle are reared. Fasciola hepatica is found in all continents except Antarctica. Fasciola gigantica has been found in some tropical areas. Except for parts of Western Europe, human fascioliasis has mainly been documented in developing countries.

People get infected by accidentally ingesting (swallowing) the parasite. The main way this happens is by eating raw watercress or other contaminated freshwater plants. Another way people might get infected is by ingesting contaminated water, such as by drinking it or by eating vegetables that were washed or irrigated with contaminated water.

No. Fasciola cannot be passed directly from one person to another. The eggs passed in the stool of infected people (and animals) need to develop (mature) in certain types of freshwater snails, under favorable environmental conditions, to be able to infect someone else.

Under unusual circumstances, people might get infected by eating raw or undercooked sheep or goat liver that contains immature forms of the parasite.

Yes. It is possible, but few cases have been reported in published articles. Some cases have been documented in Hawaii, California, and Florida.

However, most reported cases in the United States have been in people, such as immigrants, who were infected in countries where fascioliasis is well known to occur.

Some infected people don’t ever feel sick.

Some people feel sick early on in the infection, while immature flukes are passing (migrating) from the intestines through the abdominal cavity and liver. Symptoms from the acute (migratory) phase can start as soon as a few days after the exposure (typically, <1–2 weeks) and can last several weeks or months.

Some people feel sick during the chronic phase of the infection, when adult flukes are in the bile ducts (the duct system of the liver). The symptoms, if any, associated with this phase can start months to years after the exposure. For example, symptoms can result from inflammation and blockage of bile ducts.

During both phases of the infection, clinical features can include fever, malaise, abdominal pain, eosinophilia, hepatomegaly (an enlarged liver), and abnormal liver tests.

See their health care provider.

The infection typically is diagnosed by examining stool (fecal) specimens under a microscope. The diagnosis is confirmed if Fasciola eggs are seen. More than one specimen may need to be examined to find the parasite. Certain types of blood tests also may be helpful for diagnosing Fasciola infection.

Yes. Fascioliasis is a treatable disease. Triclabendazole is the drug of choice. It is given by mouth, usually in two doses. Most people respond well to the treatment.

People can protect themselves by not eating raw watercress and other water plants, especially from Fasciolaendemic grazing areas. As always, travelers to areas with poor sanitation should avoid food and water that might be contaminated. No vaccine is available to protect people against Fasciola.

This information is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the parasites described above or think that you may have a parasitic infection, consult a health care provider.

Page last reviewed: March 27, 2019