ABSTRACT
Objective To analyze the spatial characteristic on the distribution of Oncomelania hupensis in mountainous regions.Methods Based on the geographic database of snail distribution in Puge county,Sichuan province,spatial autocorrelation analysis and spatial scan statistics were applied to analyze the spatial characteristic of snail distribution.Results With regard to the rate of frame with snails,the global Moran's I indicator was 0.095(P<0.05),which indicated the spatial autocorrelation of snail distribution in Puge county.Data from the local spalial autocorrelation analysis showed that there were 28 snail habitats with statistically significant differences on local indicators of spatial autocorrelation(LISA)value(P<0.05),among which existed high-high,low-low,low-high and high-low four types of correlation model.The Spatial Scan Statistics had in total identified 24 snail habitat clusters(P<0.05),including 14 high rate clusters and 10 low rate clusters,and the result was similar to that of LISA analysis.Conclusion There were spatial autocorrelation and spatial aggregation of snail distribution in mountainous regions,meanwhile spatial heterogeneity of snail distribution also existed.This law could be explored for beaer control of snails.
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Objective To detect the snail habitats from the marshland of Eastern Dongting Lake Area, using the Remote Sensing (RS) and Geographic Information System (GIS) technology based on the China-Brazil Earth Resources Satellite-02B (CBERS-02B) CCD images. Methods According to the two typical traits of snail habitats in marshland including "water in summer and land in winter" and "no grass, no snails" , the "water in summer and land in winter" region and the vegetation coverage region were calculated by RS image processing respectively. The two regions mentioned above were then overlapped to confirm the snail habitats through comparing with the data from field survey under spatial overlapping of Arcgis as the last step. Results In Eastern Dongting Lake area, the "water in summer and land in winter" region and vegetation coverage region were predicted based on the formula normalized difference water index (NDWI) >0.01 and normalized difference vegetation index (NDVI) >0.36, respectively. The snail habitat was determined by theme overlay of the two regions said above.The agreement rate between the prediction and the geospatial data of field survey was 93.55% , which demonstrated the final results were credible and reliable. Conclusion CBERS-02B image could be used to detect the snail habitats and to monitor the changes of them, so as to find out the characteristics of distribution and the trends of diffusion. The snail index (discriminant 1 and 2) seemed to be suitable for the detection of snail habitats in the marshland of Lake area and used for the programs of snail control.
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Objective To explore the impact and regularity of snail population after changing of water level and to develop effective control and prediction programs. Methods A typical snail habitat closed to Changjiang county in Yueyang city, Hunan province was selected as the survey field.Data on water level and the changing trend of snail population during 2001-2009 including the average water level, maximum and minimum water levels, snail and infected snail densities,proportion of sampling frames with living and infected snails etc. were collected. The distribution of water level and snail indexes were described and a general additive model(GAM)for the relationships between these indexes were also fitted. Results Impacts of the average water level and the watered-out days in current year in the surveyed field on the snail density were statistically significant(P＜0.01), showing a quadratic curve association. The snail density remained at the lowest level when the average water level was at 25.0 m and the surveyed field watered-out days was 120. The average water level in current year and the field watered-out days in the past year showed statistically significant impacts on the infected snail density(P＜0.001), the proportion of sampling frames with infected snails(P＜0.05)and living snails(P value neared 0.05), presented a quadratic curve, a cubic curve or even a more complicated piecewise curve association. Both the infected snail density and the proportion of sampling frames with infected snails remained at the lowest level when the average water level was at 25.0 m and the watered-out days in the past year was 110, while the proportion of sampling frames with living snails kept the lowest level when the average water level was at 25.0 m and the watered-out days in the past year was 160. Conclusion The water level and the field watered-out days affected the development of snail population directly. The changing water level had an impact on snail population change, which mainly presented as nonlinear smooth function relation. Impact of the field watered out days on the infected snail density and the proportion of sampling frames with living snails and infected snails showed a hysteresis effect. The snail density was predicted to be retaining a high level when the water level was 24.0 m and the field watered-out days was 3 months. It had obvious advantages to fit the relationship of the changing water level and the snail indexes with a GAM which could get closer to the reality as well as easier to find and explain the potential associations and regulations.
ABSTRACT
Objective To anderstand the metagenesis of Oncomelania snails in the mountainous regions so as to control the spread of snails and the epidemics of schistosomiasis.Methods Observation spot was established at a typical snail habitat close to Puge county,Sichuan province from February 2008 to July 2009.Random sampling was applied to determine the place of each frame during the observation.All the snails in each frame were collected and numbers counted in the laboratory,with the number of mating pairs in each frame also observed.Snails being collected were measured for the body indices and the dissection was carried out to identify gender composition.survival status and the number of live snails in each frame counted.Line graphs of the body indices.mating pairs in each observed months,bar graphs of the snail density,proportions of gender together with the maturity of the snails in each month were drawn.Results The number of live snail existed the whole year and its density fluctuated.All the three kinds of body indices showed the same time trend and a dynamic circulation.The young snail existed all year around and arose constantly in proportion from May,becoming the dominant snailin October to replace the adult snails.The young and adult snails also showed a dynamic alternative.The gender composition showed no significant difference during each month.The number of the mating pairs was more on April.May and June annually,when were the snail's main multiplying stage.Conclusion In mountain area.the young snails existed through all the year while adult snails appeared to be dominantin each month except for October.Oncomelania snail showed a circular process of metagenesis which started in May and finished in October.The snail population presented a dynamic equilibrium.It was concluded that ecological studies on Oncomelania snail were extremely relevant,either to optimally apply the existing control measures or to develop alternative measures for snail control,ecologically or biologically.
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Objective To detect and analyze the clusters of schistosomiasis on marshland and lake areas based on geographic information system (GIS) in 2008 and to provide suggestions for the development of integrated methodology on the detection of clusters on related diseases. Methods Moran' s I of global spatial autocorrelation, Getis-Ord Gi of local spatial autocorrelation and SaTScan were used to detect the schistosomiasis clusters based on GIS and comparison of the results for different methods were performed. Results Results from the global Moran' s I tests for all the marshland and lake areas related to the schistosomiasis were statistically significant (P＜0.05)and indicated spatial heterogeneity; the z-score outcomes as calculated by Getis-Ord Gi indicated high cluster that 50 clusters were categorized at the 0.05 significance level and the z-score of these 45 clusters were more than 0. Results of SaTScan statistics appeared the same as local spatial autocorrelation and almost showing the existence of 5 cluster areas. Conclusion The geographical distribution of clusters where schistosomiasis was prevalent showed that it was closely corresponded to the middle and lower Yangtse river and in particular, many clusters were located near the boundary of Hubei and Hunan province.
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Objective To explore the relationships between micro-ecological environmental factors and the density of Snails so as to provide information for the elimination of Snails and control of Schistosomiasis disease,under ecological methods.Methods A bottomland close to Junshan Park in Yueyang city,Hunan province was selected as the field for survey during 10,2007-10,2008,and a systematic sampling method was applied to determine the specific sites of Snail investigation.All the Snails in each frames were collected and the soil surface temperature and vegetation coverage in several frames were measured.30 g soil sample in each selected frames were also collected simultaneously.The number of live Snails in each frame was counted by dissection,and soil measured pH value and soil moisture were tested in the laboratory.The distribution of Snails and microecological environmental factors,fitted general additive model for the relationship of these factors and the Snail density were described.Results 104 frames were surveyed,with pH value as between 4.70-7.92,vegetation coverage as in 1% to 96%,soil surface temperature as in 14.5-32.7℃,the soil moisture as in 0.07-2.00.Under General additive model,data showed that there was no significant difference for vegetation coverage.However,other factors were all significantly different(P＜0.001).It was found that a nonlinear relationship was existing between these factors and the Snail density.Conclusion Smoothing function relationship was noticed between the Snail density and micro-ecological environmental factors.It's suggested to fit general additive model to study the relationship between the distribution of Snails and its influencing factors,so as to adopt appropriate measures to change the related ecology to control the diffusion and reproduction of Snails.