Fasciola hepatica (the sheep liver fluke) and Fasciola gigantica,
parasites of herbivores that can infect humans accidentally.
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 many species of the genus Lymnae. In the snail the
parasites undergo several developmental stages (sporocysts
The cercariae are released from the snail
encyst as metacercariae on aquatic vegetation or other surfaces.
Mammals acquire the infection by eating vegetation containing
metacercariae. Humans can become infected by ingesting metacercariae-containing
freshwater plants, especially watercress
After ingestion, the metacercariae excyst in the duodenum
migrate through the intestinal wall, the peritoneal cavity, and the
liver parenchyma into the biliary ducts, where they develop into adults
In humans, 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 75 mm) reside in the
large biliary ducts of the mammalian host. Fasciola hepatica
infect various animal species, mostly herbivores.
occurs worldwide. Human infections with 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. Infections
with F. gigantica have been reported, more rarely, in Asia,
Africa, and Hawaii.
During the acute
phase (caused by the migration of the immature fluke through the hepatic
parenchyma), manifestations include abdominal pain, hepatomegaly, fever,
vomiting, diarrhea, urticaria and eosinophilia, and can last for
months. In the chronic phase (caused by 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.
identification of eggs is useful in the chronic (adult) stage. Eggs can
be recovered 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 actual
infection but from recent ingestion of infected livers containing eggs.
This situation (with its potential 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 useful especially in
the early invasive stages, when the eggs are not yet apparent in the
stools, or in ectopic fascioliasis.
comparison with other intestinal parasites.
with other flukes, Fasciola hepatica infections may not respond
to praziquantel. The drug of choice is triclabendazole with bithionol
as an alternative.