Life Cycle

Clonorchis sinensis is a small fluke (10 to 25 mm) that lives in the biliary tree of its host-- not actually in the liver-- for a period of as much as fifty years. The fluke feeds on mucosal secretions in the biliary tree and passes operculated eggs into the faeces. Once the eggs reach fresh water they are ingested by an intermediate snail host.

The flukes develop and multiply within the snail and the cercariae are released and penetrate freshwater fish. Infection of humans occurs after eating pickled, salted, raw or dried fish infected with the metacercariae. The larvae are released in the duodenum and they proceed to enter the bile duct. They then migrate to second-order bile ducts where the flukes mature into the adult forms in about one month.


Life cycle.

To give more detail, the embryonated eggs are discharged in the biliary ducts and in the stool of an infected host. Then, once they reach fresh water, the eggs are ingested by a suitable operculate snail intermediate host; more than 100 species of snails can serve as intermediate hosts, making eradication or control of the reservoir nearly impossible. In this first intermediate host), the eggs hatch to produce a miracidium. Inside the snail, the miracidia multiply asexually through a single generation of sporocysts and two generations of rediae to form a fork-tailed cercariae.

The cercariae are released from the snail and after a short period of free-swimming time in water, they come in contact with and penetrate the flesh of freshwater cyprinid fish (such as grass carp or pond smelt, both popular food fish in Asia), where they lose their tails and encyst in the scale or muscle of the fish as metacercariae. Infection of humans occurs by ingestion of undercooked, salted, pickled, or smoked freshwater fish "vector".

After ingestion, the metacercariae excyst in the host's duodenum and ascend the biliary tract by way of the ampulla of Vater. The maturation of the larvae, as mentioned previously, takes approximately 1 month. The adult flukes (measuring 10 to 25 mm by 3 to 5 mm) reside in the small and medium sized biliary ducts. In addition to humans, carnivorous animals including both wildlife and domestic animals can serve as reservoir hosts, making transmission particularly easy and control difficult.