Segmentina hemisphaerula: A new molluscan intermediate host for Echinostoma cinetorchis in Korea

Three species of Planorbidae have been reported from Korea, Gyraulus convex iusculus, Hippeutis (Helicorbis) cantori, and Segmentina (Polypylis) hemisp haerula. Of these, only H. cantori was reported as the first and second int ermediate host for Echinostoma cinetorchis, an important human intestinal p arasite in Korea. Segmentina hemisphaerula has also been found to be an int ermediate host. In field-collected planorbids, only S. hemisphaerula was fo und shedding echinostome cercariae and infected with metacercariae of E. ci netorchis, whereas no G. convexiusculus and H. cantori were found to be inf ected. In experiments with laboratory-bred snails, G. convexiusculus and S. hemisphaerula were susceptible to infection by miracidia of E. cinetorchis , but H. cantori could not be infected. Tadpoles of Rana nigromaculata and laboratory-bred snails of the 3 planorbid species were exposed to E. cineto rchis cercariae shed from field-collected S. hemisphaerula. All tadpoles, S . hemisphaerula, and G. convexiusculus became infected, but no H. cantori w ere infected. Metacercariae from tadpoles, S. hemisphaerula, and G. convexi usculus were fed to rats per os, and eggs of E. cinetorchis were detected i n the rat feces I wk later. The rats were killed, and adult E. cinetorchis were recovered from the small intestines. This is the first report of G. co nvexiusculus as a potential first and second intermediate host and of S. he misphaerula as a new first and second intermediate host for E. cinetorchis in Korea.