Fasciola hepatica - James Madison University



Fasciola hepatica

A. Classification

Phylum Platyhelminthes (flatworms)

Class: Trematoda (flukes)

Fasciola hepatica (“sheep liver fluke”)

This parasite is found most commonly in the liver of animals such as cows and sheep, however it can reside in other hosts such as horses or humans.

B. Morphology

Adult Fasciola hepatica has a flat body with a characteristic leaf shape; the anterior end being broader than the posterior end. It measures 20 to 30 mm long by 8 to 15 mm wide.

The eggs are approximately 140 µm in length 80 µm wide. They look almost identical to Fasciolopsis buski eggs.

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C. Lifecycle and Epidemiology

1. Adults parasites reside in the bile duct, where they produce eggs that are passed in the host’s feces. These eggs are unembryonated and development takes about two weeks.

2. A mobile miracidium then hatches from the egg and penetrates its first intermediate host, a snail.

3. In the snail, a sporocyst is formed, which then develops into a redia, followed by the cercarial stage. After five to seven weeks of development, the cercariae leave the snail with a body and tail.

4. The cercariae then encyst on vegetation forming a metacercaria. The metacercarial cyst is only moderately resistant, but in the right conditions (high humidity and cool temperatures) it can survive up to a year.

5. The metacercaria excysts in the host’s small intestine after being ingested and migrates through the abdominal cavity over a period of seven, finally residing in the liver. 6. After about six weeks the parasite enters the bile duct, where it fully matures to an adult parasite about 3 months after initial infection.

7. The release of eggs completes the life cycle. F. Hepatica can survive many years in the liver, laying between 20,000 and 50,000 eggs per day.

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D. Geographic Distribution

Fasciola hepatica is found all over the world; in parts of the United States, as well as in Great Britian, Ireland, Europe, the Middle East, the Far East, Africa, and Australia. It is found in both temperate and tropical regions. Human infections of 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. An estimated 2.4 million cases exist worldwide, and incidence apparently has increased since 1980.

E. Pathology and symptoms

Many people may be asymptomatic and not show any sign of infection for several years.

In Humans:

• Abdominal pain

• Vomiting

• Diarrhea

• Malaise

• Fever

• Mild jaundice

• Anemia

• Eosinophilia

•

Fatalities are rare and only in extreme cases.

In other animals:

• Low productivity (low weight gain, low milk production, etc)

• Death

•

Because F. Hepatica is not adapted to using humans as a host, the flukes may give rise to ectopic infections, being found encysted in the lungs or under the skin. The ingestion of an infected raw liver can cause Halzoun, which means that the worm has settled in the pharynx causing bleeding and an interference with respiration.

F. Diagnosis

The eggs are microscopically identified in a stool sample. They are indistinguishable from the eggs of Fasciolopsis buski. Antibody detection can be used in the early stages of infection when the eggs are not yet apparent in the feces. “Ultrasound can be used to visualize the adult flukes in the bile ducts and a CT scan may reveal the burrow tracts made by the worm and dilation of the bile ducts.” These methods are very expensive.

G. Treatment of individual

Fasciola hepatica infections may not respond to praziquantel, unlike other flukes. Bithionol is available in most countries and is the only treatment, requiring a 5-10 day course of 30mg/kg body weight. But because of the high dose and high cost of the treatment it is difficult for large-scale use. Recently, triclabendazole has been proven to be nearly 100% successful at much lower doses than bithionol; only 1-2 oral doses of 10mg/kg body weight in a 24 hour period is very effective, but it is still unavailable in many countries.

H. Public Health issues & Eradication

Control of fluke levels in the environment is very important and can be somewhat accomplished by:

• Snail control (molluscicides)

• Pasture drainage

• Chemical treatment on sheep and beef properties

• Dosing animals to kill the flukes

• Public education

o Keeping domestic animal herds away from sites of aquatic growth

o Washing of vegetables and plants

Fun Fact: Fasciola hepatica was the earliest trematode to be reported with the first references in 1379.

Works Cited

20 January 2005. “Symptoms of Fascioliasis.” Wrong Diagnosis.

. 26 January 2005.

Brenn-White, Maris of Stanford University, 2001, “Fascioliasis.” ParaSites Homepage

26 January 2005

Center for Disease Control, 26 January 2005, “Fascioliasis”, Parasites and Health,

26 January 2005

“Graphic Images of Parasites.” Parasites and Parasitological Resources, , 26 January 2005

Medicine Net. March 14, 2004.”Fasciola hepatica.” Medical Dictionary, definitions of popular medical terms . January 26, 2005

, “Liver Fluke-Fasciola hepatica”, A World of Petcare,

, 26 January 2005

Sellami, Elloumi, Cheikhrouhou, Makni, Baklouti, and Ayadi. “Fasciola hepatica infestation with joint symptoms.” Joint Bone Spine. Elsevier B.V. Feb. 1 2003. V 70. Issue 1. p. 71-72.

University of Cambridge, Department of Pathology, Schistosomiasis Research Group, 5th October 1998, “Fasciola hepatica, The Liver Fluke”, Helminthology and General Parasitology Pages, , 26 January 2005

Carrie Graham

Erin Hoffman

Kevin Louder

January 28, 2005

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