title: The influence of natural factors on the spatio-temporal distribution of Oncomelania hupensis.
abstract: BACKGROUND
  We analyzed the influence of natural factors, such as temperature, rainfall, vegetation and hydrology, on the spatio-temporal distribution of Oncomelania hupensis and explored the leading factors influencing these parameters. The results will provide reference methods and theoretical a basis for the schistosomiasis control.
  
  
  METHODS
  GIS (Geographic Information System) spatial display and analysis were used to describe the spatio-temporal distribution of Oncomelania hupensis in the study area (Dongting Lake in Hunan Province) from 2004 to 2011. Correlation analysis was used to detect the natural factors associated with the spatio-temporal distribution of O. hupensis. Spatial regression analysis was used to quantitatively analyze the effects of related natural factors on the spatio-temporal distribution of snails and explore the dominant factors influencing this parameter.
  
  
  RESULTS
  (1) Overall, the spatio-temporal distribution of O. hupensis was governed by the comprehensive effects of natural factors. In the study area, the average density of living snails showed a downward trend, with the exception of a slight rebound in 2009. The density of living snails showed significant spatial clustering, and the degree of aggregation was initially weak but enhanced later. Regions with high snail density and towns with an HH distribution pattern were mostly distributed in the plain areas in the northwestern and inlet and outlet of the lake. (2) There were space-time differences in the influence of natural factors on the spatio-temporal distribution of O. hupensis. Temporally, the comprehensive influence of natural factors on snail distribution increased first and then decreased. Natural factors played an important role in snail distribution in 2005, 2006, 2010 and 2011. Spatially, it decreased from the northeast to the southwest. Snail distributions in more than 20 towns located along the Yuanshui River and on the west side of the Lishui River were less affected by natural factors, whereas relatively larger in areas around the outlet of the lake (Chenglingji) were more affected. (3) The effects of natural factors on the spatio-temporal distribution of O. hupensis were spatio-temporally heterogeneous. Rainfall, land surface temperature, NDVI, and distance from water sources all played an important role in the spatio-temporal distribution of O. hupensis. In addition, due to the effects of the local geographical environment, the direction of the influences the average annual rainfall, land surface temperature, and NDVI had on the spatio-temporal distribution of O. hupensis were all spatio-temporally heterogeneous, and both the distance from water sources and the history of snail distribution always had positive effects on the distribution O. hupensis, but the direction of the influence was spatio-temporally heterogeneous. (4) Of all the natural factors, the leading factors influencing the spatio-temporal distribution of O. hupensis were rainfall and vegetation (NDVI), and the primary factor alternated between these two. The leading role of rainfall decreased year by year, while that of vegetation (NDVI) increased from 2004 to 2011.
  
  
  CONCLUSIONS
  The spatio-temporal distribution of O. hupensis was significantly influenced by natural factors, and the influences were heterogeneous across space and time. Additionally, the variation in the spatial-temporal distribution of O. hupensis was mainly affected by rainfall and vegetation.
authors.affiliation: School of Geosciences and Info-Physics, Central South University, Changsha, China.
authors.forename: Gong
authors.initials: G
authors.lastname: Cheng
authors.affiliation: School of Geosciences and Info-Physics, Central South University, Changsha, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Li
authors.affiliation: State Key Laboratory of Resources and Environmental Information Systems, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China.
authors.forename: Dafang
authors.initials: D
authors.lastname: Zhuang
authors.affiliation: State Key Laboratory of Resources and Environmental Information Systems, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China. Electronic address: wangy@igsnrr.ac.cn.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000818:Animals; D002681:China / Q000453:epidemiology; D004197:Disease Reservoirs / Q000469:parasitology*; D017753:Ecosystem; D005618:Fresh Water / Q000469:parasitology; D040362:Geographic Information Systems; D055593:Geological Phenomena; D060106:Lakes / Q000469:parasitology; D063245:Plant Development; D011891:Rain; D012044:Regression Analysis; D012552:Schistosomiasis / Q000469:parasitology / Q000517:prevention & control / Q000635:transmission*; D012554:Schistosomiasis japonica / Q000469:parasitology / Q000635:transmission; D012908:Snails / Q000254:growth & development / Q000469:parasitology; D062211:Spatio-Temporal Analysis
keywords: Natural factors; Oncomelania hupensis; Schistosomiasis japonica; Snail control; Spatial regression analysis