Abstract
The Three Gorges Dam, located in the largest endemic area of schistosomiasis in China, is one of the world’s largest hydroelectric projects to date. Some large-scale hydro projects have resulted in schistosomiasis emergence or re-emergence. Therefore, the dam’s potential impact on the transmission of Schistosoma japonicum has raised concerns from medical researchers worldwide. A systematic literature review, coupled with an analysis of data on the water level and snail density in the Yangtze River was conducted to assess the impact of the dam on schistosomiasis transmission after more than 10 years of operation. The dam has significantly altered the water levels in the Yangtze River according to different seasons. These changes directly impact the ecology of the schistosome snail host. Due to the dam, there has been a reduction in the density of Oncomelania snails and/or changes in the distribution of snails. The prevalence of infection with S. japonicum has decreased in the downstream areas of the dam, including in the Dongting and Poyang Lakes. The prevalence of infection with S. japonicum in humans has decreased from 6.80 % in 2002 (before the dam began operating) to 0.50 % in 2012, and the number of people infected with S. japonicum have decreased from 94 208 in 2002 to 59 200 in 2011 in the Poyang Lake region. The presence of the dam does not seem to affect snail breeding or the prevalence of schistosomiasis in the Three Gorges Reservoir. Overall, the Three Gorges Dam has significantly contributed to changes in hydrology after more than 10 years of the dam operating. The changes caused by the dam, together with integrated control of schistosomiasis, might be accelerating the progress towards eliminating the transmission of S. japonicum in the middle and lower reaches of the Yangtze River. Despite the positive effect the dam is having in controlling S. japonicum transmission, continued surveillance is required to monitor the future ecological impacts of the dam over the long term.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-016-0156-3) contains supplementary material, which is available to authorized users.
Highlights
The Three Gorges Dam, the world’s largest dam, is located in the upper reaches of the Yangtze River, the longest river in Asia and the third longest in the world.The middle and lower reaches of the Yangtze River are the largest endemic area of schistosomiasis in China [1]
For the regions below the dam, most of the studies consistently reported that the Three Gorges Dam would decrease the probability of flooding and cause changes in the water level in these areas of the Yangtze River; that is, upon completion of the dam, the water level would rise during the first part of the year and decrease during the last two or three months of the year
Most of the studies consistently predicted that the decreased the probability of flooding due to the Three Gorges Dam would limit the dispersal of the snails and reduce the chance of human and livestock making contact with water that is infested with the cercariae of S. japonicum
Summary
The Three Gorges Dam, the world’s largest dam, is located in the upper reaches of the Yangtze River, the longest river in Asia and the third longest in the world. The middle and lower reaches of the Yangtze River are the largest endemic area of schistosomiasis in China (see Fig. 1) [1]. The two largest lakes in China (Poyang Lake in Jiangxi Province and Dongting Lake in Hunan Province), which are located along the middle and lower reaches of the Yangtze River, constitute a shallow lake group unique in the world that extensively exchanges water with the river. The two lakes are endemic areas of schistosomiasis. Oncomelania hupensis hupensis snails, the intermediate snail hosts, are distributed strictly in the Yangtze River basin due to its so-called ‘winter-land, summer-
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