title: Three Gorges Dam: Impact of Water Level Changes on the Density of Schistosome-Transmitting Snail Oncomelania hupensis in Dongting Lake Area, China.
abstract: BACKGROUND
  Schistosomiasis remains an important public health issue in China and worldwide. Oncomelania hupensis is the unique intermediate host of schistosoma japonicum, and its change influences the distribution of S. japonica. The Three Gorges Dam (TGD) has substantially changed the ecology and environment in the Dongting Lake region. This study investigated the impact of water level and elevation on the survival and habitat of the snails.
  
  
  METHODS
  Data were collected for 16 bottomlands around 4 hydrological stations, which included water, density of living snails (form the Anxiang Station for Schistosomiasis Control) and elevation (from Google Earth). Based on the elevation, sixteen bottomlands were divided into 3 groups. ARIMA models were built to predict the density of living snails in different elevation areas.
  
  
  RESULTS
  Before closure of TGD, 7 out of 9 years had a water level beyond the warning level at least once at Anxiang hydrological station, compared with only 3 out of 10 years after closure of TGD. There were two severe droughts that happened in 2006 and 2011, with much fewer number of flooding per year compared with other study years. Overall, there was a correlation between water level changing and density of living snails variation in all the elevations areas. The density of living snails in all elevations areas was decreasing after the TGD was built. The relationship between number of flooding per year and the density of living snails was more pronounced in the medium and high elevation areas; the density of living snails kept decreasing from 2003 to 2014. In low elevation area however, the density of living snails decreased after 2003 first and turned to increase after 2011. Our ARIMA prediction models indicated that the snails would not disappear in the Dongting Lake region in the next 7 years. In the low elevation area, the density of living snails would increase slightly, and then stabilize after the year 2017. In the medium elevation region, the change of the density of living snails would be more obvious and would increase till the year 2020. In the high elevation area, the density of living snails would remain stable after the year 2015.
  
  
  CONCLUSIONS
  The TGD influenced water levels and reduced the risk of flooding and the density of living snails in the study region. Based on our prediction models, the density of living snails in all elevations tends to be stabilized. Control of S. japonica would continue to be an important task in the study area in the coming decade.
authors.affiliation: Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Fudan University, Shanghai, China; Center for Tropical Disease Research, Fudan University, Shanghai, China.
authors.forename: Jin-Yi
authors.initials: JY
authors.lastname: Wu
authors.affiliation: Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Fudan University, Shanghai, China; Center for Tropical Disease Research, Fudan University, Shanghai, China.
authors.forename: Yi-Biao
authors.initials: YB
authors.lastname: Zhou
authors.affiliation: School of Epidemiology, Public Health and Preventive Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Yue
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Environmental and Global Health, College of Public Health and Health Professions, University of Florida, Gainesville, Florida, United States of America; Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Song
authors.initials: S
authors.lastname: Liang
authors.affiliation: Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Fudan University, Shanghai, China; Center for Tropical Disease Research, Fudan University, Shanghai, China.
authors.forename: Lin-Han
authors.initials: LH
authors.lastname: Li
authors.affiliation: Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Fudan University, Shanghai, China; Center for Tropical Disease Research, Fudan University, Shanghai, China.
authors.forename: Sheng-Bang
authors.initials: SB
authors.lastname: Zheng
authors.affiliation: Anxiang Office of Leading Group for Schistosomiasis Control, Changde, Hunan Province, China.
authors.forename: Shao-ping
authors.initials: SP
authors.lastname: Zhu
authors.affiliation: Hunan Institute for Schistosomiasis Control, Yueyang, Hunan Province, China.
authors.forename: Guang-Hui
authors.initials: GH
authors.lastname: Ren
authors.affiliation: Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Fudan University, Shanghai, China; Center for Tropical Disease Research, Fudan University, Shanghai, China.
authors.forename: Xiu-Xia
authors.initials: XX
authors.lastname: Song
authors.affiliation: Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Fudan University, Shanghai, China; Center for Tropical Disease Research, Fudan University, Shanghai, China.
authors.forename: Qing-Wu
authors.initials: QW
authors.lastname: Jiang
mesh_terms: D000818:Animals; D002681:China / Q000453:epidemiology; D004197:Disease Reservoirs / Q000469:parasitology; D017753:Ecosystem; D055868:Floods; D005618:Fresh Water / Q000469:parasitology; D006801:Humans; D060106:Lakes / Q000469:parasitology; D011157:Population Dynamics; D012549:Schistosoma japonicum / Q000502:physiology*; D012552:Schistosomiasis / Q000453:epidemiology* / Q000635:transmission; D012908:Snails / Q000254:growth & development* / Q000469:parasitology