Pyrethroid-impregnated bed nets in the malaria control strategy at community level.

As early as 1910 Ross recommended bed nets as a protection against infective bites of vector anophelines. Bed nets also provide an efficient protection against many other biting insects and are an element of comfort. But despite this protective effect they did not significantly decrease the risk of infection and of morbidity in highly endemic areas (Snow et al., 1988a). Impregnation of bed nets with ‘knock-down acting’ .pyrethroid insecticides (deltamethrin, permethrin) with a long residual effect improved their capacity for protecting sleepers even if the net is in poor condition or not properly maintained, as is often the case in the field. Significant decreases in parasitaemia and in the incidence of malaria cases were indeed observed among children sleeping under impregnated nets in The Gambia (Snow et al., 1987), Papua New-Guinea (Graves et al., 1987) and Burkina Faso (Carnevale et al., 1988). The main advantage of impregnated nets is not only the direct protection of sleepers but also its potential as a tool for a mass campaign when used by most of the community members. Bed nets act as traps baited by sleepers attracting and, when impregnated, killing selectively the anthropophilic mosquitoes. Mosquitoes are killed before biting and not after as is the case in house spraying, which is an important entomological and psychological advantage; in this way the possible irritant and repellent effect of the insecticide is synergistic with its lethal effect in breaking the man/vector contact. Mosquito populations, and above all their mean longevity, have been drastically reduced. As a consequence of this protective and insecticide action, malaria incidence has decreased by more than 95% in a district of China where the entire population slept under deltamethrin-impregnated nets (Li Zuzi et al., unpublished). In a hyperendemic area of Burkina Faso we have observed that the collective use of impregnated nets in a village of 1200 people reduced the transmission by 90% even for those not sleeping under nets (Carnevale et al., 1988). As already emphasized (Mouchet, 1987), pyrethroid-impregnated bed nets could be a major weapon for malaria control when used by most of the community