Application of GIS to the characterization of filariasis transmission in Narathiwat Province.

The geographical information system (GIS) and available survey data (both from the Filariasis Annual Reports, 1985-1999 and from the published literature) for the microfilarial infection rates are used to develop the first subdistrict-level endemicity maps of lymphatic filariasis in Narathiwat Province. The maps demonstrated the subdistrict-level geographical distribution of filariasis and the subdistricts at varied degrees of infection rate. The maps also indicate that, since 1985, there was a marked decrease in endemicity at the subdistrict level and in some areas, the infection rates were zero. However, transmission remained in the subdistricts surrounding peat swamp forest (Su-ngai Padi, Paluru, Puyo, Pasemat, Bang Khunthong, and Phron subdistricts). The house locations of infected cases, as well as the vector breeding places were geo-registered and placed as symbolic dots on the base maps obtained from Landsat's Thematic Mapper (TM) 5 and the land use map of Narathiwat to display the distribution of filariasis foci. Of 102 houses mapped, there were 40 houses in primary peat swamp forest (39.22%), 26 in rice fields (25.49%), 15 in fruit orchards (14.70%), 10 in coconut fields (9.80%) and others (10.78%). All the houses were close to the larval habitats presented in the survey. A 2-km buffer zone around the conservation boundary of primary peat swamp forest was created to locate risk areas of filariasis transmission. The buffer zone covered an area of 544.11 km2 and included 88.89% of the houses of infected cases found in 2002. It was able to identify 54 villages located in the buffer area, which might help in the determination of resource needs and resource allocation for filariasis control in Narathiwat Province.