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
- 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.
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