Fasciola hepatica

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

Geography

·         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

Pathology

·         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

Diagnosis

·         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

Treatment

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

Epidemiology

·         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