EFFECTS OF COMMUNITY-WIDE USE OF LAMBDACYHALOTHRIN-IMPREGNATED BEDNETS ON MALARIA VECTORS IN RURAL SIERRA-LEONE

The effect of community-wide use of bednets treated with lambdacyhalot hrin 10 mg/m(2) on the malaria vector Anopheles gambiae (forest form) was evaluated in Sierra Leone. Sixteen similar villages near the town of Bo were randomly allocated either to remain without nets or to rece ive treated bednets for all inhabitants, with effect from June 1992. M osquitoes were sampled using human biting catches on verandas, light-t rap catch (beside an occupied untreated bednet), window exit-trap catc h and pyrethrum spray collections. During the first year of interventi on (June 1992 to July 1993) the treated bednets provided personal prot ection for people sleeping under them, but had very little impact on d ensities of An.gambiae collected on human bait. The human blood index (HBI) of An.gambiae was not affected (HBI = 99% in villages with and w ithout nets). An.gambiae parous rates were significantly reduced in al l intervention villages, but malaria sporozoite rates fell in only som e of the villages. These results are intermediate between those obtain ed from other projects in Tanzania and Burkina Faso, where treated bed nets reduced man-biting, parity and sporozoite rates, versus The Gambi a where treated bednets had no significant impact on any of these fact ors. Possible reasons for these contrasted findings are discussed.