Influence of deltamethrin treatment of bed nets on malaria transmission in the Kou valley, Burkina Faso.

A 3-year entomological study was carried out on the transmission of malaria in a village of 900 inhabitants in a rice-growing area of Burkina Faso. In the study area inhabitants use bed nets to protect themselves from mosquito bites. In the first year of the study, baseline data were collected; in the second year, the village was divided in two parts and all the bed nets in the southern part were sprayed with deltamethrin (25 mg/m2); and in the third year, all the bed nets in both parts of the village were sprayed. The inoculation rate was estimated by hand collection of mosquitos on human volunteers who were not protected by bed nets. The overall inoculation rate in the first year was 55 infected bites per person and was higher in the southern than in the northern part of the village. During the second year the rate increased to 70 bites per person on average (but was slightly lower than this in the southern part of the village). During the third year, the inoculation rate fell to three infected bites per year, i.e., a reduction of 94% compared with the first year. This reduction arose primarily because of a marked decrease in the sporozoitic index and a lower density of vectors. Thus, use of pyrethroid-impregnated bed nets by all members of the community appears to be a major tool in preventing transmission of malaria.