Construction of the Three Gorges Dam across the Yangtze River will substantially change the ecology of the Dongting Lake in southern China. In addition, the Chinese Central and Hunan Provinces' governmental authorities have instigated a Return Land to Lake Program that will extend the Dongting Lake surface area from the current 2,681 [km.sup.2] to 4,350 [km.sup.2].The previous construction of embankments and the large silt deposits made by the Yangtze River and other connecting ...
<1 year of age (24). The use of domesticated buffaloes as working animals by farmers will continue to provide reservoirs for S. japonicum. Schistosome infections due to occupational exposure may therefore reemerge in areas where schistosomiasis was previously reduced or eliminated, while compliance for diagnostic testing and treatment in Dongting Lake communities can be low (25,26). A recent longitudinal study that looked at schistosomiasis prevalences over 9 years (1997-2006) among mobile populations in Jicheng and Qingshanhu villages in the Dongting Lake region confirms these concerns (Figure 6). Jicheng and Qingshanhu are located in areas where the Return Land to Lake Program has been implemented; these 2 locations were occupied over time by migrants who pursued their economic activities, including fishing and animal farming. As a result, the prevalence of schistosomiasis increased steadily among the migrants and their animals. In Jicheng, persons remained engaged in fishing and animal fanning during the whole study period, whereas in Qingshanhu, persons switched to industrial fish cultivation after 2001. Fish cultivation is a protective factor; thus, schistosomiasis prevalence decreased among these migrants, whereas in Jicheng, the prevalence of the disease continued to increase. Another study (Y.-K. He, unpub. data) on Dongting Lake showed that after persons were relocated from disease-endemic areas to 27 disease-endemic or -nonendemic villages, disease prevalence substantially increased in the former (Figure 7). Schistosomiasis prevalence decreased as the distance between the villages and Dongting Lake increased. Furthermore, schistosomiasis was again endemic in villages where it had previously been successfully eliminated. Another study showed that people who had been relocated from the Dongting Lake to hilly areas were at a decreased risk for infection with S. japonicum (28). On the other hand, migrants from disease-nonendemic areas, or areas where schistosomiasis was controlled, who are relocated to endemic areas will be at a high risk for infection because of limited natural immunity (i.e., persons never exposed to schistosomiasis) or diminished immunity (i.e., persons formerly exposed). Official statistics indicate that 5 new rural communities have been built around Dongting Lake for>