The pathological changes are more or less related to the intensity and the duration of the infection, and are commonly seen in older patients with a large number of flukes. The pathogenesis is due to the mechanical irritation by the flukes and some toxic substances produced by them. Lesions are mainly confined to the biliary system. There is hyperplasia of the epithelial cells lining the bile ducts. In heavy and severe infections there are obstruction of the biliary tract, bile retention, extensive hyperplasia of the biliary system, with glandular proliferation of papillomatous and adenomatous type, cholangitis, periductal infiltration with eosinophils, round cells and fibrosis in the portal areas, necrosis and atrophy of hepatic cells. The bile ducts are dilated and in late cases saccular or cystic formations may develop into large cysts. The gallbladder may enlarge and contain white bile. The liver profile is generally normal. The majority of cases are symptomless. Clinical features vary from mild to severe. The symptoms and signs are vague gastro-intestinal symptoms, flatulence, anorexia, lassitude, weight loss, dull pain at the right hypochondrium, hot cutaneous sensation of the abdomen, and enlargement of the liver with some tenderness. In few cases the manifestations are severe. There is relapsing cholangitis, the patient is seriously ill and may succumb to septic shock. Cholangiocarcinoma, gallstones and obstructive jaundice are not unusual associations.