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

Flukes of the genera Fasciola(hepatica, gigantica), Opisthorchis, and Clonorchis all may infect the human biliary tract and at times produce manifestations of ductal obstruction. C sinensis is the Chinese liver fluke. Infection with any of these three species is established by ingestion of raw or inadequately cooked freshwater fish harboring metacercariae. These organisms encyst in the duodenum, releasing larvae that travel through the ampulla of Vater and mature into adult worms in bile canaliculi. Mature flukes are flat and elongated, measuring 1-2 cm in length. The hermaphroditic worms reproduce by releasing small operculated eggs, which pass with bile into the intestines and are voided with stools. The life cycle is completed in the environment in specific freshwater snails (the first intermediate host) and encystment of metacercariae in freshwater fish. Moderate to heavy infection may be associated with vague right-upper-quadrant pain. In contrast, chronic or repeated infection is associated with manifestations such as cholangitis, cholangiohepatitis, and biliary obstruction. Ref: Mahmoud A.A. (2012). Chapter 219. Schistosomiasis and Other Trematode Infections. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.