Liver flukes are found predominantly in China, Japan, Korea, and Vietnam. The definitive hosts include grazing herbivores, such as sheep and cattle, as well as dogs, cats, rabbits, and humans. Eggs passed in the feces are deposited in the environment and hatch in freshwater areas within 10 days, longer if temperatures are cool. They are known to survive in cold water for several years. The embryos develop into miracidia, which swim to and penetrate the soft tissue of snails. The miracidia undergo several developmental stages (sporocysts, rediae, cercariae) within the snail and are then released and penetrate freshwater fish (second intermediate host). There they encyst as metacercariae in the muscles or under the scales of the fish. People become infected by ingesting undercooked fish or raw or undercooked vegetables containing metacercariae. After ingestion, the metacercariae excyst in the duodenum and ascend through the ampulla of Vater into the biliary ducts, where they attach and develop into adults, laying eggs after 3 to 4 weeks. Adult flukes reside in the biliary and pancreatic ducts, where they attach to the mucosa.