INFLUENCE OF DELTAMETHRIN IMPREGNATED BED NETS ON THE BITING BEHAVIOROF ANOPHELES-GAMBIAE IN DJOUMONA, CONGO

Several studies recently done in Africa south of the Sahara have clear ly demonstrated that pyrethroid impregnated bednets should actually re duce malaria inoculation rate due to Anopheles gambiae and therefore h igh Plasmodium falciparum parasitaemia and malaria morbidity, even mor tality. Nevertheless some concerns were recently raised on an eventual shift in the usual behavior of this species induced by the presence i nside the house of bednets treated with pyrethroid insecticide known t o have a deterrent or excito-repellent effect, and which could therefo re lead to a biting behavior earlier than usual. The current limited s tudy, done in Djoumouna, a place well known for the very high density of An. gambiae, has shown that the temporary presence inside a house o f a bednet impregnated with deltamethrin (12,5 or 25 ma a.i./m2) has n ot induced any shift in the biting cycle of this species, but it actua lly reduced by some 50% its biting rate noticed on human beings. It is worth underlining that all sporozoite infected specimens were actuall y caught after midnight. This biting behavior of An. gambiae could exp lain why impregnated bednets are so efficient in reducing man-vector c ontact and malaria transmission.