The deceptive simplicity of using insecticide-treated nets for malaria control

Jacob Koella

University of Neufchâtel, Switzerland

Jacob.koella@unine.ch

Our simplistic view of insecticides is that they kill insects, and thus reduce the damage they cause, until their extensive use leads to the evolution of resistance. I will argue that, when insecticides are used to control malaria, when the goal is to reduce transmission of the parasite rather than the number of mosquitoes, the story is far less simple, and far more interesting.  One reason is that insecticides not only kill but also repel mosquitoes. Therefore, using an insecticide-treated bednet (one of our most effective and most widely used ways of controlling malaria) protects the individual users from being infected by repelling some of the mosquitoes and on the other hand, and it protects their community by killing others. But mosquitoes that are repelled are not killed, so there is conflict between personal and community protection. A second reason is that malaria parasites affect how mosquitoes respond to insecticides: infectious mosquitoes, for example, are far less likely to be repelled than uninfected ones. The parasite thus changes the balance between personal and community protection. A third reason is that the environment has a large impact on the effect of an insecticide and on the infection by malaria. During larval growth, for example, food conditions affect the sensitivity of mosquitoes to insecticides, and sub-lethal doses of insecticides affect the immune response of the mosquitoes and thus whether they are infected by malaria. I will review my group’s work on such interactions between mosquitoes, insecticides and malaria, discussing examples of the mosquito’s behavior, its physiological basis and some mathematical modeling.