Larval Trematodes from Fresh-water Snails in Cheongdo county, Kyongbuk, Korea

Abstract

In order to determine the incidence of cercarial larvae of trematodes, the snail intermediate hosts collected in Cheongdo River, an endemic area of Clonorchis sinensis in Kyongbuk Province, Korea, were studied from June, 1997, to October, 1998. Four kinds of larval trematodes, Cyathocotyle orientalis, C. sinensis, Exorchis oviformis, and Loxogenes liberum were found from Parafossarulus snails examined. Of these, L. liberum was found frequently liberated cercaria with 1.75%, followed by C. ori¬entalis with 0.91% and E. oviformis with 0.3%. The least frequently liberated was C. sinensis with 0.12%. The infection rates showed variation with the shell length of Parafossarulus snail. Among the Semisulcospira snails examined, seven species of larval trematodes and 3 kinds of undetermined cercariae were found in 70 snails, which becomes an overall infection rate of 3.8%. Of these, the most frequently emerged cercaria was C. orientalis with 1.14%, followed by Cercaria nipponensis with 0.6%, Cercaria incerta with 0.49%, and cercaria of Metagonimus species with 0.43%. In general, the larval trematodes began to emerge from May, and peak in their emergency were found in July. The present study indicates that cercarial larvae of trematodes in the snail intermediate hosts are less infective than those of several decades ago.