Satellite climatology and the environmental risk of Schistosoma mansoni inEthiopia and east Africa

Annual and seasonal composite maps prepared From the normalized difference vegetation index (NDVI) and earth surface maximum temperature (T,,,,) satel lite data from the archives of the Global land I-km program of the United S tates Geological Survey (USGS) were studied For. their potential value, usi ng geographic information system (GIS) methods, as surrogates of climate da ta in the development of environmental risk models for schistosomiasis in E thiopia. Annual. wet season and dry season models were developed and iterat ively analyzed for relationships with Schistosoma mansoni distribution and infection prevalence rates. Model-predicted endemic area overlays that best fit the distribution of sites with over 5% prevalence corresponded to valu es of NDVI 125-145 and T-max 20-33 degreesC in the annual composite map, ND VI 125-145 and T-max 18-29 degreesC for the wet season map, and NDVI 125-14 0 and T-max 22-37 degreesC for the dry season map. The model-predicted ende mic area was similar to that of a prior model developed using an independen t agroecologic zone data set from the United Nations Food and Agriculture O rganization (FAO). Results were consistent with field and laboratory data o n the preferences and limits of tolerance of the S. mansoni-Biomphalaria pf eifferi system. Results suggest that Global 1-km NDVI acid T-max when used together, can be used as surrogate climate data for development of GIS risk assessment models for schistosomiasis, The model developed for Ethiopia ba sed on global 1-km satellite data was rxtrapolated to a broader area of Eas t Africa. When used with FAO agroecologic zone climate data limits of < 27 degreesC for average annual mean temperature and annual moisture deficits ( annual rain-annual potential evapotranspiration) of < - 1300 mm, the model accurately represented the regional distribution of the S.,mansoni-B. pfeif feri system in the East Africa extrapolation area. (C) 2001 Elsevier Scienc e B.V. All rights reserved.