Monitoring Parasitic Disease Transmission through Radar Altimetry and Hydrologic Modeling: Schistosomiasis in Poyang Lake, China

Schistosomiasis is the second-most prevalent tropical disease after malaria affecting two-hundred million people annually world-wide. This chronic disease shortens lifespan on average by ten years in endemic areas and no vaccine exists. The current control methods of human host chemotherapy and application of molluscicides to the environment do not break the disease transmission cycle. Schistosomiasis transmission in southern China involves an amphibious intermediate host snail. Hydrology is a key factor in snail ecology because the adults need moist vegetation while the juveniles are fully aquatic. Thus, hydrology is a key factor in schistosomiasis transmission and understanding its role can shape control measures. Our objective is to integrate hydrologic, ecologic, and other environmental factors to determine the changes in available snail habitat through space and time. We use radar altimetry measurements to determine water level every 35 days when the Envisat (Environmental Satellite) passes over the lake. The radar altimetry readings have been calibrated to levels from in-situ gauging stations and will support remote analysis of disease transmission potential without the need for gauging station data. A geographic information system was used to combine key factors including water level, topography, and air temperature data to identify areas of available snail habitat. In order to accomplish this, we conducted three steps including: delineating the watershed, specifying potential snail habitat areas through topography and air temperature classification, and calculating the intersection between potential snail habitat and non-flooded areas in the watershed. Statistical analyses of total available habitat area are also conducted. These maps and statistics analyses can be used by public health agencies to monitor snail habitat trends over time. This technique for monitoring snail habitat will continue to be important as the hydrology of the lake changes due to the completion of upstream Three Gorges Dam project.