A man on return from a country complains of pain in abdomen, jaundice, with increased alkaline phosphatase and conjugated hyperbilirubinemia. USG shows blockage in the biliary tree. What could be the cause -

CLONORCHIS SINENSIS Commonly known as the Chinese liver fluke, Embryonated eggs are discharged in the biliary ducts and in the stool . Eggs are ingested by a suitable snail intermediate host . Each egg releases a miracidia , which go through several developmental stages (sporocysts , rediae , and cercariae ). The cercariae are released from the snail and after a sho period of free-swimming time in water, they come in contact and penetrate the flesh of freshwater fish, where they encyst as metacercariae . Infection of humans occurs by ingestion of undercooked, salted, pickled, or smoked freshwater fish . After ingestion, the metacercariae excyst in the duodenum and ascend the biliary tract through the ampulla of Vater . Maturation takes approximately 1 month. The adult flukes (measuring 10 to 25 mm by 3 to 5 mm) reside in small and medium sized biliary ducts. In addition to humans, carnivorous animals can serve as reservoir hosts. The migration of the larva up the bile duct induces desquamation, followed by hyperplasia and sometimes adenomatous changes. The smaller bile ducts undergo cystic dilatation. The adult worm may cause obstruction and blockage of the common bile duct leading to cholangitis. Chronic infection may result in calculus formation. A few cases go on to biliary cirrhosis and poal hypeension. Some patients with chronic clonorchiasis tend to become biliary carriers of typhoid bacilli. Chronic infection has also been linked with cholangiocarcinoma. Patients in the early stage have fever, epigastric pain, diarrhoea and tender hepatomegaly. This is followed by biliary colic, jaundice and progressive liver enlargement. Many infections are asymptomatic REF:TEXTBOOK OF MEDICAL PARASITOLOGY;CKJ PANIKER;6TH EDITION;PAGE NO 128