Indoor residual spraying for preventing malaria

Abstract

Spraying houses with insecticides (indoor residual spraying; IRS) to kill mosquitoes is one of the main methods that have been used to control malaria on a large scale. IRS has helped to eliminate malaria from great parts of Asia, Russia, Europe, and Latin America, and successful IRS programmes have also been run in parts of Africa. Another successful method of mosquito control relies on the use of physical barriers such as bednets or curtains that can also be sprayed with insecticides (insecticide treated nets; ITN). This review aims to look at the health benefits of IRS and to compare this method with ITNs. This review does not assess the potentially adverse effects of insecticides used for IRS, and it includes not only randomized controlled trials (RCTs), but also controlled before-and-after studies (CBA) and interrupted time series (ITS), as these methods were considered suitably rigorous. Six studies were identified for inclusion (four cluster RCTs, one CBA and one ITS). Four of these studies were conducted in sub-Saharan Africa, one in India and one in Pakistan. IRS reduced malaria transmission in young children by half compared to no IRS in Tanzania (an area where people are regularly exposed to malaria), and protected all age groups in India and Pakistan (where malaria transmission is more unstable and where more than one type of malaria is found). When compared with ITNs, IRS appeared more protective (according to the outcome chosen) in one trial conducted in an area of stable malaria transmission, but ITN seemed to be more protective than IRS in unstable areas. Unfortunately, the level of evidence is very limited and no firm conclusions should be drawn on the basis of this review. In conclusion, although IRS programmes have shown impressive success in malaria reduction throughout the world, there are too few well-run trials to be able to quantify the effects of IRS in areas with different malaria transmission, or to properly compare IRS and ITN. High-quality and long-duration trials on a large scale, done in areas where there has been little or no mosquito control are still urgently required. New trials should include an IRS arm and an ITN arm, and should also assess the combined effect of ITN and IRS, a very important question in view of malaria elimination