Study was conducted by gathering natural ocurring snails, Bithynia spp., in Ha Noi, Hai Duong and Nam Dinh provinces. It was determined that Bithynia snail is the intermediate host of Clonorchis sinensis. Bithynia mainly occurs in calm water with the rate of 58.27 percent
The prevalence of Cercaria infection Clonorchis sinensis varied from 0.32 to 4.78 percent. Laboratory study showed that 100 percent snails float on the water surface in summer, 93.34 percent snails settle to mud
100 percent snail lay eggs in summer and fall with hatching interval between 9 to 12 days. The study on micro-lesions of liver and bile ducts of cat infected by natural Clonorchis sinensis has shown that bile duct wall was thickened and fibrized, some ducts were obstructed with the hyperplasia. Inflamative cells of eosinophil, plasmacyte, lymphocyte and macrophage appeared around. Other symptoms include hepatic congestion, radial capillary expansion with infiltration of erythrocyte
central vein area of small lobe and interlobular vein expanded widely with infiltration of erythrocytes. Hepatocytes were found with fatty degeneration and vacuolar degeneration.