Fasciola hepatica life cycle.
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1. Unembryonated eggs are discharged into the biliary ducts and excreted in feces.
2. Eggs become embryonated in water.
3. Eggs release miracidia, which invade a snail (intermediate host).
4. In the snail, the parasites progress through several developmental stages (sporocysts, rediae, and cercariae).
5. The cercariae are released from the snail and encyst as metacercariae on aquatic vegetation or other surfaces.
6. The infection is acquired by eating plants, especially watercress, containing metacercariae.
7. After ingestion, the metacercariae excyst in the duodenum.
8. They migrate through the intestinal wall, peritoneal cavity, and liver parenchyma into the biliary ducts, where they develop into adults.
Image from the Centers for Disease Control and Prevention Image Library.