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Over the several decades, China has been incessantly optimizing control strategies in response to the varying epidemic situations of schistosomiasis. We evaluated continuously the changing prevalence under different control strategies of two villages, Sanlian and Guifan, in China through five phases lasting 37 years. We tested residents, calculated prevalence and discussed change causes. We found the prevalence in Sanlian did not differ significant from that of Guifan (p = 0.18) in 1981, but decreased to 2.66%, much lower than Guifan&rsquo, s 11.25%, in 1984 (p = 0). Besides, prevalence in Guifan increased to 21.25% in 1987, while in Sanlian it rose to 20.78% until 1989. Those data confirmed that praziquantel combined with snail control could better reduce the prevalence. From 1992 to 1994, the prevalence in the two villages displayed downtrends, which showed the World Bank Loan Project worked. From 1995 to 2004, repeated oscillations with no obvious change trend was seen. Since 2005, the prevalence in both villages has shown a significant downtrend (p &lt, 0.05), which suggests the integrated strategy is effective. We considered the control strategies were implemented suitably in the study area under changing social circumstances. Adjusting the strategy in consideration of social transformations is necessary and vital. The experience may be useful for policy making of other epidemic areas with an analogous situation.

Background Schistosomiasis remains an important public health issue in China and worldwide. Oncomelania hupensis is the unique intermediate host of schistosoma japonicum, and its change influences the distribution of S. japonica. The Three Gorges Dam (TGD) has substantially changed the ecology and environment in the Dongting Lake region. This study investigated the impact of water level and elevation on the survival and habitat of the snails. Methods Data were collected for 16 bottomlands around 4 hydrological stations, which included water, density of living snails (form the Anxiang Station for Schistosomiasis Control) and elevation (from Google Earth). Based on the elevation, sixteen bottomlands were divided into 3 groups. ARIMA models were built to predict the density of living snails in different elevation areas. Results Before closure of TGD, 7 out of 9 years had a water level beyond the warning level at least once at Anxiang hydrological station, compared with only 3 out of 10 years after closure of TGD. There were two severe droughts that happened in 2006 and 2011, with much fewer number of flooding per year compared with other study years. Overall, there was a correlation between water level changing and density of living snails variation in all the elevations areas. The density of living snails in all elevations areas was decreasing after the TGD was built. The relationship between number of flooding per year and the density of living snails was more pronounced in the medium and high elevation areas; the density of living snails kept decreasing from 2003 to 2014. In low elevation area however, the density of living snails decreased after 2003 first and turned to increase after 2011. Our ARIMA prediction models indicated that the snails would not disappear in the Dongting Lake region in the next 7 years. In the low elevation area, the density of living snails would increase slightly, and then stabilize after the year 2017. In the medium elevation region, the change of the density of living snails would be more obvious and would increase till the year 2020. In the high elevation area, the density of living snails would remain stable after the year 2015. Conclusion The TGD influenced water levels and reduced the risk of flooding and the density of living snails in the study region. Based on our prediction models, the density of living snails in all elevations tends to be stabilized. Control of S. japonica would continue to be an important task in the study area in the coming decade., Author Summary Oncomelania hupensis, an amphibious animal, is the unique intermediate host of schistosoma japonicum. Three Gorges Dam (TGD) is a tremendous hydrological project, and it influences the survival of animals downstream. It is studied for several reasons. First, schistosomiasis is still a world-wide parasitic disease which needs to be prevented and controlled. Second, TGD causes the change of water level, and it will impact the existence of snails, but how TGD causes the change of snails and even the epidemics of schistosomiasis is not revealed. In this study, the authors explore the association between TGD and snails. The time-series data contains over 10-year water level downstream TGD and 10-year density of living snails downstream TGD in Dongting Lake Region. These can help to find out the relationship between the change of water level and the change of density of living snails. After this exploration, we attempt to predict the density of living snails 7years later using ARIMA model.

To study the reasons of natural death of Oncomelania hupensis snails in marshland by comparing the differences of environmental factors between snail marshland and non-snail marshland in East Dongting Lake schistosomiasis endemic areas.Two adjoining marshlands were selected, one was a snail marshland and another was a non-snail marshland. The measuring points were set by grid of "20 m x 20 m". The soil moisture, elevation, soil pH and temperature of the points were measured, and the snails of the points were surveyed.The elevation, soil pH and temperature of the snail natural death marshland were all lower than those of the snail marshland (P0.01). The soil moisture, elevation, soil pH and temperature of different snail densities in the snail marshland were different (P0.05). The soil moisture of the non-snail group was higher than that of other four groups (P0.01) and the soil moisture of the group with 0-11 snails per frame was lower than that of other four groups (P0.01). The elevation of the group with 0-11 snails per frame was lower than that of the group with 24-39 snails per frame and the group with more than 39 snails per frame (P0.05). The soil pH of the group without snails was higher than that of other four groups (P0.01) and the soil temperature of the group with 0-11 snails per frame was lower than that of the group with 24-39 snails per frame. The differences of soil moisture and elevation of different death snail densities were not significant, while the differences of soil pH and temperature were significant. The soil pH of the non-snail died group was higher than that of the 2-died, 3-died and more than 3-died groups (P0.05). The soil temperature of the non-snail died group was higher than that of other four groups (P0.05).The elevation, soil pH and soil temperature within the range of the research may be the factors affecting the snail natural death and the soil moisture, elevation, soil pH and soil temperature may be the factors affecting the distribution of snails.

To understand the change trend of Oncomelania hupensis snails in the bottomland areas of Qian Liang Lake district in Eastern Dongting Lake area so as to provide the evidence for formulating a schistosomiasis control strategy.The monitoring data of snails of Qianliang Lake district from 1988 to 2011 were collected retrospectively and analyzed by using the method of the trend Chi-square test. The correlations among the snail density indicators were analyzed.1988 to 2011, the area of snails surveyed did not change and was 433.2 hm(2). The monitoring data showed that the change trend of the density of living snails and the schistosome infection rates of snails were not obvious (P0.05), but the mortality of snails showed a falling trend (P0.05); There were positive correlations between the average density of infected snails and the mortality of snails (r = 0.640, P0.05) , the infection rate of snails (r = 0.639, P0.05) , and the average density of living snails (r = 0.646, P0.05) , respectively. There was no correlation among other snail indicators. In 1999, only 7 snails were found, of them, only one snail was alive. The alive snails were not found after 2000.In the bottomland areas of Qianliang Lake district, the change trend of the density of alive snails were not obvious from 1988 to 1998, but the number of snails underwent a sharp drop in 1999 and snails have been not found till now.

To evaluate the effects of comprehensive measures with emphasis on schistosomiasis infectious source control at the embankment level.The comprehensive measures with emphasis on schistosomiasis infectious source control were carried out, and the data of human and Oncomelania snail infection rates were collected and analyzed statistically at embankment levels.In Anbao Embankment, except the other comprehensive measures were performed, 2606 buffaloes were removed. The infection rates of residents reduced from 8.04% before the intervention to 0.7% after the intervention, and the infection rates of snails reduced from 0.56% to 0.05%. In Anli Embankment, 535 buffaloes were removed. In the third year after the intervention, the infection rates of residents reduced from 5.87% to 1.09%, and the infection rates of snails reduced from 0.17% to 0.07%. In Anzao Embankment, 62 buffaloes were removed. In the second year after the intervention, the infection rates of residents reduced from 2.67% to 0.39%, and the infection rates of snails reduced from 1.12% to 0.00%. In Anchang Embankment, the buffaloes were not removed. The human infection rates reduced from 1.76% before the intervention to 1.23% after the intervention.The comprehensive measures with emphasis on schistosomiasis infectious source control, especially the buffalo's removal, are effective in the control of schistosome infection rates of residents and snails.