1. In people, adult flukes release eggs through the bile ducts into the intestine. Fluke eggs are passed in stool (feces).
2. In the environment, the eggs are ingested by snails. Inside the snail, the eggs go through several stages to develop into an immature form of the fluke that has a tail and can swim (cercariae).
3. The cercariae penetrate the skin of a freshwater fish and form cysts in the tissues of the fish.
4. People are infected when they consume the cysts in raw, undercooked, salted, pickled, or smoked freshwater fish, or sometimes freshwater shrimp.
5. In the intestine, the larvae leave the cysts.
6. The larvae travel back up the intestine into the bile duct and then into the liver or gallbladder. There, they develop into adults and produce eggs.
Image from the Centers for Disease Control and Prevention Image Library.