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Causal Agents:The trematodes Fasciola hepatica (the sheep liver fluke) and Fasciola gigantica, parasites of 

herbivores that can infect humans accidentally.

Life Cycle:

Immature eggs are discharged in the biliary ducts and in the stool . Eggs become

embryonated in water , eggs release miracidia , which invade a suitable snail

intermediate host , including the genera Galba, Fossaria and Pseudosuccinea. In the snail

the parasites undergo several developmental stages (sporocysts , rediae , and cercariae

). The cercariae are released from the snail and encyst as metacercariae on aquatic

vegetation or other surfaces. Mammals acquire the infection by eating vegetationcontaining metacercariae. Humans can become infected by ingesting metacercariae-

containing freshwater plants, especially watercress . After ingestion, the metacercariae

excyst in the duodenum and migrate through the intestinal wall, the peritoneal cavity,

and the liver parenchyma into the biliary ducts, where they develop into adults . Inhumans, maturation from metacercariae into adult flukes takes approximately 3 to 4

months. The adult flukes (Fasciola hepatica: up to 30 mm by 13 mm; F. gigantica: up to 75mm) reside in the large biliary ducts of the mammalian host. Fasciola hepatica infect

various animal species, mostly herbivores.

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Geographic Distribution:Fascioliasis occurs worldwide. Human infections with F. hepatica are found in areas wheresheep 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, inAsia, Africa, and Hawaii.

Clinical Features:During the acute phase (caused by the migration of the immature fluke through the hepaticparenchyma), manifestations include abdominal pain, hepatomegaly, fever, vomiting,

diarrhea, urticaria and eosinophilia, and can last for months. In the chronic phase (causedby the adult fluke within the bile ducts), the symptoms are more discrete 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. Eggs can berecovered in the stools or in material obtained by duodenal or biliary drainage. They are

morphologically indistinguishable from those of Fasciolopsis buski . False fascioliasis

(pseudofascioliasis) refers to the presence of eggs in the stool resulting not from an actualinfection but from recent ingestion of infected livers containing eggs. This situation (with itspotential 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 usefulespecially in the early invasive stages, when the eggs are not yet apparent in the stools, or

in ectopic fascioliasis.

Diagnostic findings

Microscopy

Antibody detection

Morphologic comparison with other intestinal parasites.

Treatment:Unlike infections with other flukes, Fasciola hepatica infections may not respond topraziquantel. The drug of choice is triclabendazole with bithionol as an alternative. For

additional information, see the recommendations in The Medical Letter (Drugs forParasitic Infections).

Antibody DetectionThe acute manifestations of human fascioliasis may precede the appearance of eggs in the stool by several weeks;immunodiagnostic tests may be useful for early indication of Fasciola infection as well as for confirmation of chronicfascioliasis when egg production is low or sporadic and for ruling out "pseudofascioliasis" associated with ingestionof parasite eggs in sheep or calves' liver. The current tests of choice for immunodiagnosis of human Fasciola

hepatica infection are enzyme immunoassays (EIA) with excretory-secretory (ES) antigens combined withconfirmation of positives by immunoblot. Specific antibodies to Fasciola may be detectable within 2 to 4 weeksafter infection, which is 5 to 7 weeks before eggs appear in stool. Sensitivity for the FAST-ELISA format of EIA wasreported to be 95%, while sensitivity for the immunoblot using 12-, 17-, and 63-kDa antigens appeared to be100%. However, some cross-reactivity occurs in the FAST-ELISA with serum specimens of patients withschistosomiasis. Antibody levels decrease to normal 6 to 12 months after chemotherapeutic cure and can be usedto predict the success of therapy.

Reference:

Hillyer GV. Serological diagnosis of Fasciola hepatica. Parasitol al Dia 1993;17:130-6.

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Microscopy

EggsEggs of Fasciola hepatica are broadly ellipsoidal, operculated and measure 130-150 µm longby 60-90 µm wide. The eggs are unembryonated when passed in feces. The eggs of F.

hepatica can be difficult to distinguish from Fasciolopsis spp., although the abopercular endof the former often has a roughened or irregular area.

A B

A, B: Eggs of F. hepatica in an unstained wet mount, taken at 400x magnification.

AdultsAdults of Fasciola hepatica are large and broadly-flattened, measuring up to 30 mm longand 15 mm wide. The anterior end is cone-shaped, unlike the rounded anterior end of 

Fasciolopsis buski . Adults reside in the bile ducts of the liver in the definitive host.

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C D

C: Unstained adult of F. hepatica fixed in formalin.D: Adult of F. hepatica stained with carmine.

E F

E, F: Adults of F. hepatica observed with endoscopic retrograde cholangiopancreatography

(ERCP) imaging in the common bile duct of a human patient. Images courtesy of Dr.Subhash Agal, Kokilaben Dhirubhai Ambani Hospital, Mumbai, India.