Geographic information systems as a tool for control program management for schistosomiasis in Egypt

During a 4-year study a geographic information system (GIS) risk model was constructed for predicting the relative risk of schistosomiasis in Kafr El- Sheikh governorate, Egypt. A 1-year 1990-1991 time series on diurnal temper ature difference (dT) prepared from the advanced very high resolution radio meter (AVHRR) sensor on the NOAA-II satellite was used to develop a regiona l risk model for the Nile delta based on thermal-hydrological domains. A Ma y 15, 1990 Landsat TM scene (path 177, Row 38) was used to develop a local 'village-scale' environmental risk model based on higher resolution satelli te sensor data (30 m picture element size at earth surface). Four of ten cl asses derived from a tasseled cap (Tcap) transformation of the Landsat TM s cene were shown to be significantly related to a 5-year Schistosoma mansoni prevalence database from the Ministry of Health. A risk model was develope d based on dT and the proportional area of the four Tcap classes in 5 km(2) buffer zones centered on rural health unit (RHU) reporting units. Availabl e historical data on S. mansoni and its snail host Biomphalaria alexandrina as well as recent field collected data were gathered and incorporated as s eparate themes. Model validation was done using data collected on snail pop ulation bionomics-infection rates, water quality, underground water table a nd cercariometry at 13 hydrologically representative sites. The role of soi l type. water table and water quality was studied at 79 of 154 rural health unit sites. The model permitted retrieval of relevant data by RHU point lo cation. For the first time in Egypt. the Kafr El-Sheikh GIS schistosoma pre diction model can support MOH efforts to make more accurate control program decisions based on environmental predilection sites of endemic Schistosomi asis mansoni. (C) 2001 Elsevier Science B.V. All rights reserved.