Chapter 11 - Mekong Schistosomiasis: Where Did It Come from and Where Is It Going?

Abstract

The schistosomiasis in humans, in Cambodia and Laos, is caused by infection with Schistosoma mekongi. The disease develops after free-swimming parasite larvae, released from a snail intermediate host, penetrate the skin during bathing. Only snails of the correct species can act as intermediate hosts for a particular Schistosoma species. The almost complete absence of S. mekongi from Laos north of the Khong Island, and its restriction in the Mekong River has traditionally been attributed to the absence of Neotricula aperta and/or unsuitable ecological conditions for transmission in this area. The place of origin of S. mekongi is probably on a part of the Sunda shelf, east of Vietnam, which is now under the sea and the Khong Island population represents a more recent colonization of Laos. At the time of the dispersal of proto-S. malayensis/mekongi from China, a vast plain of wetlands and rivers existed to the east of present day Vietnam; these alkaline wetlands would be ideal habitats for triculine snails. Rising sea levels would have reduced the habitat area down to only the rivers southwest of the Annam range in Cambodia and to those of West Malaysia.