Abstract
This study was implemented at the fringe of the malaria epidemic zone, in villages on western slopes of the central highlands, outside the area covered for the past five years by routine DDT housespraying (OPID). Four types of treatment were compared in different areas: 1) DDT 2 g ai/m 2 and 2) lambda-cyhalothrin 30 mg ai/m 2 in previously unsprayed villages, 3) no intervention (control); 4) yearly DDT spraying (OPID fifth cycle). To investigate the malariological impact of spraying, cross-sectional surveys of the village populations were performed in each study area at intervals of two months, before and after spraying. In the newly sprayed areas, from December to June, malaria indices decreased by 62 % in the ICON ® area and 44 % in the DDT area, whereas in the unsprayed village malaria increased by 32 % during the same season. There was a similar decrease in the number of gametocyte carriers in the newly sprayed areas. Active malaria case detection among febrile individuals was performed fortnightly in each village outside the OPID area. Results showed decreased malaria incidence from February (two months post-spraying) in the sprayed villages, despite the rainy season, whereas in the unsprayed area the décline occurred only after the main transmission season. This study demonstrated that, parasitologically as well as entomologically, house-spraying with residual insecticide (DDT or ICON®| was an effective method for controlling malaria on the western fringes of the Madagascar highlands epidemic zone. Both products were effective, but ICON ® had slightly better impact than DDT, i.e. more reduction of malaria indices and of vector longevity, less irritancy of mosquitoes. For best results in this area of transition between stable and unstable malaria, we recommend earlier annual spraying (as soon as November) and extension of the OPID barrier towards western and northern slopes of the Plateau.