LIFE CYCLE
Centers for Disease Control and Prevention Website

A cycle of human infection begins when the embryonated eggs of the parasites O. viverrini and O. felineus are passed through the feces of an infected mammal and enter the water habitat of the first intermediate host, a freshwater snail of the genus Bithynia.
Inside their snail host, the eggs hatch in the alimentary canal of the snail and are now call miracidia. The miracidia penetrate the intestine and develop into sporocysts. The sporocysts develop into radiae and mature into cercariae in the digestive gland of the snail.
The cercariae leave the snail and penetrate the second intermediate host, a freshwater fish. They encyst as metacercariae in the muscles or under the scales of the fish. The definitive host of the parasite is the mammal that ingests an undercooked fish containing the metacercariae.
Once ingested, the metacercariae excyst in the duodenum and travel to the biliary ducts where they attach and develop into adults that lay eggs after 3-4 weeks. This adult "liver fluke" will live in the biliary and pancreatic ducts of the host and attach to the mucosa.

Life cycle of both O. viverrini and O. felineus in Opithorchiasis infection
Image from the Centers for Disease Control and Prevention website

RESERVOIR/VECTOR
Mehlorn (2001)

Dogs, cats, and other fish eating mammals are the reservoir for the parasites that cause human infections of Opisthorchiasis. There is not a vector of this parasite.

TRANSMISSION
Centers for Disease Control and Prevention Website, Mehlorn (2001)

Humans become infected through ingestion of raw, pickled, or poorly cooked fish that contain the metacercariae of the parasite. Infected humans and other mammals excrete the eggs of the parasite through their feces. The first intermediate host, a freshwater snail, which is often Bithynia leachi, ingests these eggs. The eggs hatch into free-swimming cercariae and implant themselves into their second intermediate host, a freshwater fish. The cycle of infection continues once these fish are eaten without proper preparation to kill the parasite