ABSTRACT
Objective With Landsat TM remote sensing images,snail habitats in Poyang Lake region were identified,using two indices:the modified normalized difference water index (MNDWI) and the normalized difference vegetation index (NDVI).Methods Two Remote sensing images of both wet and drought seasons in Poyang Lake region were obtained.MNDWI and NDVI were extracted from the images respectively,to present the regions of “water in summer and land in winter” and the coverage of vegetation.By overlaying those two regions,the areas of potential snail habitats were drawn.Finally,sensitivities and specificities of the recommended methods were assessed and compared to that of the traditional methods for the sake of extracting the areas of snail habitats.Results The threshold values of MNDWI for the wet and drought seasons were 0.34 and 0.58,respectively and the threshold value for NDVI of the drought season was 0.02.Sensitivity and specificity of our method were 95％ and 100％,respectively,higher than the conventional approach (se.=75％,sp.=100％ ).Conclusion Joint application of MNDWI and NDVI seemed a better method to detect the snail habitats and could be used for the quantitative and automatic surveillance program on snails.
ABSTRACT
Objective To evaluate the effect of an integrated control strategy and to quantify the spatial-temporal variation of infected snails in the bottomland areas after the strategy was implemented.Methods Based on the geographic database of infected snail distribution at the village level during 2004-2010 in Anxiang county,Hunan province,spatial autocorrelation analysis and spatial scan statistics were applied to analyze the spatial-temporal characteristics on the distribution of infected snails.Results The number of embankments with infected snails in Anxiang county decreased from 23 in 2004 to 10 in 2010,while the rate of frame with infected snail in embankments decreased from 4.32‰ in 2004 to 0.12‰ in 2010.The spatial distribution of infected snails was nonrandom,only in 2004 and 2005 with Moran's I=0.21 (P＜0.10) and Moran's I=0.13 (P＜0.10) respectively.Data from the local spatial auto-correlation analysis showed that the number of villages with H-H types of auto-correlation model had been gradually decreasing.The results of SaTScan statistics appeared the same as from the local spatial auto-correlation analysis,showing that the number of areas with increased risk was decreasing.Conclusion The comprehensive measures with emphasis on infectious source control seemed effective for schistosomiasis control program.The current distribution characteristics provided us with evidence that the resource assignment could be more reasonably implemented so as to control schistosomiasis in a more effective way.