Impact of Changing Water Levels and Weather on Oncomelania hupensis hupensis Populations, the Snail Host of Schistosoma japonicum, Downstream of the Three Gorges Dam

Abstract

Increasing evidence indicates that dams impact riverine ecosystems and human diseases. Poyang Lake, one of the largest schistosomiasis endemic environments in China, will change due to the construction of the Yangtze River Three Gorges Dam. We assess changes in Oncomelania hupensis hupensis, the snail host for Schistosoma japonicum, in response to changing water levels and weather from 1998 to 2002. In the 5 years following the major flooding of Poyang Lake in 1998, seasonal water levels have gradually decreased, concomitant with decreases in mean and variance of fall snail densities. Nonlinear relationships suggest that the highest spring density is associated with current, 2-, and 3-month prior temperatures of 18 degrees, 9.1 degrees, and 5.8 degrees C, while the highest fall density is associated with 2- and 3-month prior water levels of 17 and 18 m, respectively. This suggests that lower, more stable water levels downstream of the dam may result in a reduction in mean fall densities and their variance. However, additional data are needed to determine whether snail populations that are typically destroyed by seasonal floods may live longer in more stable environments created by the dam.

Impact of the Three Gorges Dam on the Hydrology and Ecology of the Yangtze River

“…In addition to adversely affecting the environment and its biodiversity, dams can also impact human health by altering the ecology of waterborne and parasitic diseases, such as schistosomiasis [43], and the Three Gorges Dam is no exception. Zhu et al [44] suggested that the Three Gorges Dam can lead to schistosomiasis epidemics by altering the environment both within the Three Gorges region and in downstream areas.…”

“…In particular, the decline in magnitude and frequency of floods can be linked to aggravation of this situation, since floods are commonly used as a method to control snail populations [45]. In this context, the report by Seto et al [43] indicates that the increased stability of water levels downstream from the dam can be linked to decreases in the mean and variance of snail densities, which may help to restrain the transmission of schistosomiasis. However, although overall snail densities may decrease with lower and more stable water levels, the density of infected snails and corresponding human infection can increase due to the co-location of buffalo grazing areas, snail habitat, and human activity that may occur due to the increased stability of water levels.…”

Energy and Human Health

“…They found that living near a dam reservoir in endemic areas is associated with more than a doubling of risk (relative risk 2.4 for Schistosoma haematobium, and 2.6 for S. mansoni ). The Three Gorges Dam is expected to increase the risk of schistosomiasis in some areas, although the risk may decrease in other areas and control programs may mitigate some of the risk (125,188,237).…”

Schistosomiasis in the People's Republic of China: the Era of the Three Gorges Dam

“…Spatial epidemiology, geographical information systems (GIS), remote sensing (RS), and the use of advanced Bayesian based spatial statistics have become important tools in China's national schistosomiasis control program over the past 10 to 15 years (82,159,173,235). A comprehensive review of these techniques with applications to the epidemiology and control of schistosomiasis in China is available (221).…”