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Impact of Water Level and Climatic Factors on the Distribution of Schistosoma Japonicum Intermediate Host Oncomelania Hupensis and the Identification of Snail Habitats in Eastern Dongting Lake Areas

Author: LiYuanPei
Tutor: JiangQingWu
School: Fudan University
Course: Epidemiology and Biostatistics,
Keywords: Water level Climatic factors Lake regions Snails Schistosomiasis Schistosome Generalized additive model Factor Analysis CBERS - 02B satellite Snail habitats Vegetation index Water Index
CLC: R184
Type: Master's thesis
Year: 2011
Downloads: 92
Quote: 3
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Abstract


One of the parasitic disease schistosomiasis is a serious threat to our health and living conditions of residents of southern, mainly in the main lakes endemic areas in Anhui, Hubei, Hunan, Jiangxi and Jiangsu provinces and mainly endemic areas of the mountainous area of popular in Yunnan and Sichuan provinces. In recent years, due to the impact of factors such as climate change, the Three Gorges dam and returning farmland to lake and natural disasters, such as floods and droughts, the middle and lower reaches of the Yangtze River water level, climate and environmental factors have undergone a corresponding change directly affects the lake regions snails breeding and distribution. This article Dongting typical snail habitats scene, explore the impact of changes in water level and climatic factors on schistosome snail intermediate host population distribution, with the help of satellite remote sensing images, combined with meteorological, hydrological and on-site survey to establish a GIS database, and then detect potential snail habitats in East Dongting Lake area, the development and implementation of measures for the control of snails, schistosomiasis transmission blocking and population health promotion provides a theoretical basis. Throughout the study is divided into three parts: the first part of the East Dongting Lake water level changes in the impact of the rise and fall of snails purpose to explore the impact of growth and decline in East Dongting Lake water level fluctuation on snails and its laws, to provide guidance based on effective control and prediction of the snails. Methods Gyaincain embankment, mayor of Yueyang, Hunan Province, a typical snail habitats for on-site water level data and snail status data collected between 2001-2009, including the average water level, the highest and lowest water level and density of living snails, positive snail density , screw frame rate and positive screw box appears rate. Describe the water level indicators and snail status indicators, time changes in the distribution, respectively, with simple models and generalized additive model (GAM) on the relationship between the water level indicators of snail indicators univariate fitting. Average water level and field flooded a number of days of live snail density were statistically significant (p lt; 0.01), expressed as a quadratic curve, the density of living snails in the average water level of 25.0m, flooding the number of days to 120 day minimum. Average water level of the year and the previous year's on-site flooding the number of days on the positive snail density and positive spiral frame rate were statistically significant (p lt; 0.001), expressed as a quadratic curve or three times and more complex sub-samples curve relationship; the screw box appears rate effects were statistically significant (p ≈ 0.05), expressed as a quadratic curve. Positive snail density and positive spiral box appears the rate of the average water level of 25.0m last year flooded the number of days to 110 days minimum, and solenoid box appears rate in the average water level of 25.0m last year flooded the number of days to 160 days minimum . Conclusion water level and flooding the length of the number of days a direct impact on the growth and decline of the snails. Of water level on the growth and decline of snails mainly as a nonlinear smooth function relationship. The days of flooding is likely to appear on the snail box rate of infected snail density and positive spiral frame rate lag effect. It can be speculated that the average water level at 24.0m, the flooded marshland days for 3 months, live snail density to maintain a high level. Relative to the simple regression model, the impact of the growth and decline of snails may be closer to the actual ease of interpretation, but also easier to detect the potential relationship between the two and laws of GAM fitting water level changes. The second part of the East Dongting Lake area of ??climatic factors on the the snail distribution of Objective explore the East Dongting Lake water level and climatic factors snail distribution, to provide theoretical support for the control of snails and human health protection. Select a typical snail habitats in East Dongting Lake area, collect the appropriate water level conditions and climate variables: temperature, humidity, rainfall and sunshine hours and snail status indicator data, combined with the factor analysis and generalized additive model (GAM) to be together to study the combined effects of climatic factors (current effect or lag effect) snail distribution. Results of temperature, precipitation, humidity, sunshine hours, the water level variables are varying degrees of contact between the water level and flooding the number of days with snail density have shown a strong correlation between the significant lag effect. The snail density obvious seasonal effect, showing a double peak in late spring and early autumn stage showed high density in a low-density level in the winter. Using factor analysis two common factors: environmental suitability index and ambient humidity index is extracted from the water level and climatic factors. GAM smoothing spline fitting effect figure shows that environmental suitability index positive linear effect and cubic curve-like non-parametric effects, when the absolute value of the index value is higher (gt; 1) or low (0 value near the snail density ) level, reduce the density of snails, snail density increased when the absolute value of the index value at a moderate level (0-1); ambient humidity index snail density showed only conic kind of non-parametric effects, when the absolute value of the index value is between 0-1, snail density increased, when the absolute value of the index value is greater than 1, the snail density. However, the humidity index relative to the appropriate index, has a more pronounced effect. Conclusion water level and the combined effect of climatic factors can be broken down as general environmental suitability index and the ambient humidity index, the former decided to large environment is suitable for the breeding of snails, the latter decided to snails breeding and survival of the state. In the overall environment for the East Dongting Lake area of ??snail habitats, environmental suitability index snail density only showed weak seasonal effect caused by the the snail density gentle change, the variation is mainly determined by the humidity and rainfall and humidity index impact. The results of this study may Lakes snail control and schistosomiasis transmission-blocking measures to develop support, but still need to follow-up study confirmed from the theoretical and practical. The third part of the East Dongting Lake area of ??marshland potential snails breeding ground for detection purposes CBERS-02B (China-Brazil Earth Resources Satellite-02B satellite CBERS-02B) CCD image, combined with remote sensing (RS) and geographic information systems (GIS ) technology to quickly identify the East Dongting Lake area of ??marshland potential snail habitats. The method combines Lakes snails suitable breeding ground for two typical characteristics: \calculate the \Last Lo bottomland geographic information point data space superimposed contrast verification to determine the accuracy of the prediction method and reliability. Results in the East Dongting Lake area, NDWI. Gt; and 0.01 determine \The region with a screw-point spatial data superimposed contrast verification in line with the rate as high as 93.55%, prompted predicted results. Conclusion CBERS-02B satellite images for the detection of the East Dongting Lake area of ??marshland snail habitats with good usability, can be found in the distribution and trends of the screw area. Snail index (discriminant 1 and 2) suitable for use in the detection of all lake regions bottomland snail habitats, to provide guidance for snail control work.

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CLC: > Medicine, health > Preventive Medicine,Health > Epidemiology and Prevention of Disease > Prevention measures and management
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