Parasitology 101 is an educational blog that that can be used as a study guide for microbiology, infectious disease and medical technology students. The “bullet-point” format keeps the information concise and to the point.

Fasciola hepatica egg  Photo/CDC
Fasciola hepatica egg Photo/CDC

General Information

  • Fasciola hepatica is a trematode or fluke also known as the “sheep liver fluke”
  • All trematodes are parasitic
  • All trematodes have a phase of their life cycle in snail or other molluscan host
  • All trematodes are associated with water
  • Facioliasis is a zoonotic disease


  • Human infection has been reported from over 60 countries, mainly in sheep-raising areas
  • Important public health problem in Latin America (Peru, Bolivia, Cuba), Russia, parts of Europe and Iran
  • Reported sporadically in the US

Morphology (adults)

  • Leaf-shaped with cephalic cone
  • 3.0 x 1.3 cm

Morphology (eggs)

  • Large, ovoid, thin-shelled, operculated, yellowish-brown in color
  • 130-150 x 90 um in size

Life Cycle

  • Adult fluke in biliary passages
  • Immature eggs are discharged in feces
  • Eggs embryonate in the water
  • Eggs hatch and release miracidia
  • Miracidia invade suitable snail host (intermediate host)
  • Development in snail (sporocyst>rediae>cercariae)
  • Cercariae leaves snail and encyst on aquatic vegetation as metacercariae
  • Metacercariae on uncooked water plant is ingested by human, sheep or cattle (F. gigantica)
  • Metacercariae excyst in the duodenum
  • Migrates through intestinal tract, peritoneal cavity and liver parenchyma into bile ducts
  • Matures into adults
  • Maturation from metacercariae to adult fluke takes up to 4 months
  • In humans, adult flukes can produce eggs for 9 years


  • Migrating flukes can cause abdominal pain, liver enlargement and fever
  • Blockage of bile ducts, portal cirrhosis, eosinophilia, jaundice, diarrhea and anemia
  • Halzoun: In humans that eat raw sheep liver. Adult flukes leave liver and attach to throat causing blockage


  • In endemic areas, symptoms suggest infection
  • History of eating uncooked watercress and water lettuce
  • Finding eggs in feces or biiary drainage. Eggs of F. hepatica and Fasciolopsis buski too similar to differentiate. Check travel history.
  • Antibody detection: enzyme immunoassays (EIA) with excretory-secretory (ES) antigens combined with confirmation of positives by immunoblot


  • The drug of choice is triclabendazole with bithionol as an alternative


  • Sheep-raising countries (and cattle) where there is a suitable snail host (Lymnea sp).
  • Where humans eat uncooked watercress and other aquatic plants in salads or on sandwiches

Prevention and Control

  • Educate public in endemic areas not to eat wild (uncooked) watercress and other water plants
  • Avoid using livestock feces to fertilize water plants
  • Treat animal infections
  • Using molluskicides

Other Information

  • False fascioliasis (pseudofascioliasis): this is the presence of eggs in the stool resulting not from an actual infection but from recent ingestion of infected livers containing eggs.
  • Have the patient follow a liver-free diet several days and repeat stool examination.
Adult Fasciola hepatica  Photo/Adam Cuerden via Wikimedia Commons
Adult Fasciola hepatica Photo/Adam Cuerden via Wikimedia Commons