Immature eggs are discharged in the biliary ducts and passed in the stool (1). Eggs become embryonated in freshwater over approximately 2 weeks (2); embryonated eggs release miracidia (3), which invade a suitable snail intermediate host (4). In the snail, the parasites undergo several developmental stages (sporocysts [4a], rediae [4b], and cercariae [4c]). The cercariae are released from the snail (5) and encyst as metacercariae on aquatic vegetation or other substrates. Humans and other mammals become infected by ingesting metacercariae-contaminated vegetation (eg, watercress) (6). After ingestion, the metacercariae excyst in the duodenum (7) and penetrate through the intestinal wall into the peritoneal cavity. The immature flukes then migrate through the liver parenchyma into biliary ducts, where they mature into adult flukes and produce eggs (8). In humans, maturation from metacercariae into adult flukes usually takes about 3 to 4 months; development of F. gigantica may take somewhat longer than F. hepatica.
Reproduced from: Fascioliasis: Parasite biology. Centers for Disease Control and Prevention. DPDx – Laboratory Identification of Parasites of Public Health Concern. https://www.cdc.gov/dpdx/fascioliasis/index.html (Accessed on June 27, 2024).
