Planorbid snails as potential molluscan intermediate host of a human intestinal fluke, Neodiplostomum seoulensis (Trematoda : Diplostomatidae) in Korea.

Three species of the pulmonate snails of the family Planorbidae have been reported from Korea; Gyraulus convexiusculus, Hippeutis (Helicorbis) cantori and Segmentina (Polypylis) hemisphaerula. Of these 3 species, only H. cantori is reported as the molluscan intermediate host of Neodiplostomum seoulensis, one of the important snail-borne human intestinal trematodes in Korea. However, S. hemisphaerula was also found to be an intermediate host for N. seoulensis. In field-collected snails, H. cantori and S. hemisphaerula were found shedding bifurcated cercariae of N. seoulensis, whereas no G. convexiusculus was found shedding cercariae. In experiments with laboratory-bred snails, only S. hemisphaerula was susceptible to miracidia of N. seoulensis. Tadpoles of Rana nigromaculata and R. rugosa were exposed to cercariae shed from field-collected and laboratory-bred S. hemisphaerula. All tadpoles of R. nigromaculata were found to be massively infected, but none of the tadpoles of R. rugosa were infected with larvae of N. seoulensis. Metacercariae from tadpoles of R. nigromaculata and the snake Rhabdophis tigrinus tigrinus were fed to rats, and eggs of N. seoulensis were detected in the rat feces one-week later. These rats were killed and adult N. seoulensis recovered from the small intestines. This is the first report of S. hemisphaerula as a molluscan intermediate host for N. seoulensis in Korea.