Research On Spatio-temporal Variation Of Schistosomiasis And Oncomelania Hupensis At Village Level And Surveillance Of Dynamic Changes Of Water Body Of Rivers And Oncomelania Hupensis Habitats

Schistosomiasis due to Schistosoma japonicum is one of the most serious parasitic causing serious damage to people’s health in China. We have got the great achievements in the national schistosomiasis control over the past60years. With the social and economic development, China’s schistosomiasis control strategies have changed accordingly. In recent years, schistosomiasis control experts proposed a new integrated strategy for transmission control of schistosomiasis which emphasized removing cattle from snail-infested grasslands, providing farmers with mechanized farm equipment, improving sanitation by supplying tap water and so on. With the implementation of the new strategy, the spatial distribution of schistosomiasis and snails has changed. In this study, the data of infection rate survey in human from2006to2010and of snail survey outside the embankment from2004to2010in Anxiang County were collected. Two variables of the infection rate in human and the rate of frame with infected snail were computed according to the data. The spatial autocorrelation analysis and spatial scan statistics were applied to analyze the spatial-temporal distribution characteristics of the two variables. The results were visualized through the software of ArcGIS. Dongting Lake exhibited a large seasonal water level fluctuation. A significant part of these marshlands constituted a major schistosome-endemic site in China. Now identifying snail habitats required considerable manpower and some areas were difficult to access. The development of geographic information system (GIS) and remote sensing (RS) provided useful tools for detecting the potential snail habitats. Successful applications of RS and GIS techniques have been reported. But previous researches have not given the standard of choosing remote sensing images. In this study. multi-temporal China-Brazil Earth Recourses satellite-02images taken in Anxiang County were collected for monitoring the water body of rivers and Oncomelania snail habitats. All of these aim to provide information for snail controlling policy decision, for the better surveillance and prediction of snail habitats and for population health promotion. The whole study included three parts:Part Ⅰ Spatial-temporal variation of schistosomiasis at village levelObjective To quantify the spatial-temporal variation of schistosomiasis in bottomland areas so as to evaluate the effect of a new integrated control strategy. Methods The infection rate surveys in human were carried out in Anxiang County. Hunan province. and the data of infection rate surveys in Anxiang County from2006to2010were collected. The spatial analysis database at the village level during2006-2010was constituted by matching the survey data with the spatial database of polygon. The spatial autocorrelation analysis and spatial scan statistics were applied to analyze the spatial-temporal characteristics of distribution of infection rate. Results The infection rate in human in Anxiang County deceased from2.06%in2006to1.15%in2010(Z=560.07, P<0.0001). The spatial clustering of global autocorrelation analysis was statistically significant from2006to2009(Moran’s I>0, P<0.05). The local spatial autocorrelation analysis showed that there were over10villages of High-High type of correlation model with statistically significant LISA value in2006,2008and2009(P<0.05), but the number of villages of High-High type of correlation model at pilot areas decreased. When the maximum spatial cluster sizes based on population thresholds was set at10%, the clusters identified contained the largest average proportion of villages with high rates. There were all more than10clusters identified by SaTScan software from2006to2010, but the position of clusters had changed. The number of clusters at pilot areas decreased and the number of villages within the clusters also decreased. Conclusion The clustering of the infection rate in Anxiang County as a whole at village level didn’t change significantly. But the numbers of villages of High-High type of correlation model and of clusters at pilot areas decreased. The comprehensive measures with emphasis on infectious source control were effective for schistosomiasis control.Part II Spatial-temporal variation of infected snail in bottomland areas at village levelObjective To quantify the spatial-temporal variation of infected snail in bottomland areas after an integrated control strategy. Methods The snail surveys outside the embankment were carried out in Anxiang County and the data of snail surveys in Anxiang County from2004to2010were collected. Then the geographic database of snail distribution was established. The spatial autocorrelation analysis and spatial scan statistics were applied to analyze the spatial-temporal characteristics of distribution of the rate of frame with infected snails. Results The number of embankments with infected snails in Anxiang County decreased from23in2004to10in2010and the rate of frame with infected snail in embankments decreased from4.32%o in2004to0.12‰in2010(Z=21.45,P<0.0001). As a whole the spatial distribution of infected snail was nonrandom only in2004and2005with Moran’s I=0.21and Moran’s I=0.13respectively. The local spatial autocorrelation analysis showed the number of villages with H-H type of correlation model decreased gradually. And the results of SaTScan statistics showed that the number of clusters of increased risk decreased at pilot areas. Conclusion The integrated control strategy with emphasis on infectious source control was effective for schistosomiasis control. According to the current distribution characteristics of infected snails, we could assign limited resource more reasonably and control schistosomiasis more effectively.Part III Application of multi-temporal China-Brazil Earth Recourses Satellite-02data on surveillance of dynamic changes of water body of rivers and Oncomelania snail habitatsObjective To study the dynamic changes of the water body of rivers and Oncomelania snail habitats by using multi-temporal China-Brazil Earth Recourses Satellite-02images taken in Anxiang County so as to establish the correct procedure for selecting images. Methods CBERS-02images were collected on20th December2003,10th February2004,10th April2004,19th June2004,10th August2004and27th October2004. Then the water body information from the study areas based on NDWI was extracted and the areas of water body were calculated to determine the images. Results The dynamic changes of the water body conformed to the rules of "water in summer and land in winter". Because of the rise of water, the water area in July was the biggest and the water area began to decline from August. The water area in April was the smallest. Then the wet season and the dry season should be June and April respectively. Conclusion The multi-temporal CBERS-02images could be used to surveillance the dynamic changes of the water area and helpful in choosing the right images of the wet season and dry season.