Map of Karuzi province showing the intervention (treated hills) and control hills. The Karuzi province is composed of "colline" (hills), represented by small polygons and regrouped in 7 communes (Buhiga, Bugenyuzi, Gitaramuka, Gihogazi, Nyabikere, Mutumba and Shombo). The dark grey polygons corresponded to the targeted hills for the vector control and light grey are the hills selected to be the control areas for the survey. The two zones (Zone 1: survey done in March-April 2001 two months after the intervention. Zone 2: survey done from October to December 2001, five months after the intervention) are separated by a thick black line.