Possible effects of the Three Gorges dam on the transmission of Schistosoma japonicum on the Jiang Han plain, China

The Three Gorges dam, under construction on the Yangtze River in China, mig ht affect the transmission of Schistosoma japonicum on the Jiang Han plain, which is downstream of the dam. To study this possibility, the prevalence of schistosomiasis was investigated in relation to a range of malacological , hydrological and meteorological factors. The general water level in the Y angzte over a year had a marked effect on the distribution of the intermedi ate host (Oncomelania hupensis) and the prevalence of human schistosomiasis in that year. Disease prevalence showed significant correlations with the density of the snail hosts, the level of the water table, annual rainfall, yearly evaporation, and altitude. Once the dam is complete, the flow of wat er downstream will probably be maintained at a level between those currentl y occurring in flood and dry weather, and this may have implications for sc histosome transmission. Systematic monitoring is necessary to investigate t he impact of the environmental changes brought about by the dam on transmis sion.