Abstract

One of the most medically important snail species of Korea is Semisulcospira spp., a member of the freshwater prosobranch family pleuroceridae. The parasites that these snails transmit to humans are mainly Paragonimus westermani and Metagonimus yokogawoi. On the other hand, Semisulcospira snails are edible as a foodstuff in Korea. The present study was first aimed to detect out residual pesticides in the snails collected at the endemic and non-endemic areas of paragonimiasis in Korea and to make relationship to the detectability of larval trematodes shed from the snails. In addition, water specimens from the habitats where the snails were collected were sampled and analysed to elucidate environmental conditions of the habitats. This malaco-ecological survey was done at 7 endemic and 3 non-endemic areas of paragonimiasis for about more than 2 years, May, 1984 through October, 1986. All the water smaples both from the endemic and non-endemic areas of paragonimiasis showed normal ranges of the criteria of upper freshwater streams, with lower B.O.D. (0.4~2.0 ppm) and higher D.O. values (9.5~11.0 ppm) than those in the large river systems Infection rate of digenetic trematodes in total snails collected was 6.7%, but no Paragonimus cercaria was detected out at all even in the endemic areas of paragonimiasis. The ecological factors affecting Paragonimus larvae in the snails were also discussed. A total of 9 chlorinated hydrocarbon pesticieds was targeted to detect out from the tissues of snails. Out of 9 pesticides, aldrin, beta-BHC, p, p-DDT, dieldrin, DDE, lindane, heptachlor and heptachlor epoxide were eluted from the snails. The highest levels of the pesticides were mostly detected out in the snails collected from the Donghae-Chun area of Haman and the Kangwha area of Kyongki-Do, where the lowest infection rates of trematode cercariae (0~0.5%) were revealed. The possibilities that the residual pesticides in the freshwater animals including Semisulcospira snails might be transferable to humans were also discussed.