AFM Bulletin #6: Recognizing the way insecticides work in malaria control - the critical importance of WHO's position on DDT

31 Jan 2011
Africa Fighting Malaria
The only proven and consistent method of insect-borne disease prevention (where a vaccine does not exist) is vector control - suppressing contact between disease-spreading vectors (mosquitoes, fleas, lice, and other insects) and humans in order to interrupt disease transmission.

Vector control is the most important method of prevention for insect-borne diseases like malaria. Yellow fever is the only major insect-borne disease for which an effective vaccine is currently in use. But even when a vaccine is available and effective, insufficient vaccination rates can lead to disease outbreaks that require vector control for containment. Insecticides remain the most important element in vector control for malaria and other important insect-borne diseases. Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are proven vector control interventions that rely heavily on safe, effective, and long-lasting insecticides.

The World Health Organization (WHO) currently recommends 12 insecticides for IRS. DDT is the oldest of these insecticides and the only one not initially developed for use in agriculture. DDT is also unique because it is the only insecticide that has three distinct modes of action, namely spatial repellency, contact irritancy and toxicity.

Although toxic resistance to DDT has been noted, even after decades of public health use, it is still one of the best and most widely used chemicals for preventing malaria transmission inside houses. The powerful spatial repellent action prevents or slows the selection of resistance in mosquitoes when used for malaria control. In fact, DDT is the only chemical recommended for malaria control that stops mosquitoes from even entering houses and thus transmitting disease. But for decades people have thought that the only good mosquito is a dead mosquito, and that DDT functions only by killing mosquitoes; both of which are seriously flawed concepts.

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