Fasciola hepatica
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.
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
Fascioliasis 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
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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.
