Fasciola hepatica is a topic covered in the Johns Hopkins ABX Guide.

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MICROBIOLOGY

  • Trematode (fluke) infection contracted in sheep/goat raising areas in temperate climates with human as accidental host.
  • Requires aquatic snail as intermediate host (e.g., Lymnaea truncatula).
    • Cercariae spread to water and encyst as metacercariae on vegetation.
    • Infection occurs by eating uncooked foods such as watercress or food made with contaminated water.
  • F. hepatica and F. gigantica are the major human pathogens.
  • F. gigantica is restricted to Africa and Asia whereas F. hepatica is found in all five continents.
    • Highest rates of F. hepatica infection have been reported from Bolivia, Peru, Egypt, Iran, Portugal, and France.
  • Life cycle: [Fig 1]
    • Herbivore (sheep or goat) sheds eggs in feces
    • Eggs hatch as ciliated miracidia
    • Miracidia infect snails
    • Miracidia hatch to cercaria
    • Cercaria shed by snails and encyst on plants ("metacercaria")
    • Humans/herbivores ingest plants
    • Cysts hatch in small intestine and burrow through intestinal wall
    • Peritoneal metacercaria burrow through liver wall
    • Metacercaria mature in liver over 2-4 months (end of acute phase)
    • Migration to biliary ducts to begin chronic obstructive phase
    • Eggs shed in feces

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Last updated: October 24, 2016