Indoor and outdoor biting behaviour of malaria vectors and the potential risk factors that enhance malaria in southern Malawi

Current methods of malaria vector control implemented by national control programmes rely mainly on the use of insecticides. These include the use of long-lasting insecticide treated nets (LLINs) and indoor residual spraying (IRS). The success of LLINs and IRS is underpinned by the protection from infectious mosquito bites provided to individuals and the reduction in mosquito population size caused by sufficient contact of mosquitoes with the insecticide in the nets or on the walls of the houses. The high degree of endophily (resting indoors) and endophagy (feeding indoors) exhibited by the dominant African malaria vectors has been, therefore, a key component of that success. However, in recent years in some regions, the biting behaviour of the African malaria vectors, both indoors and outdoors and during a wider range of times than previously recognized, has been reported. This has an implication on malaria control because individuals are at risk of receiving infectious bites from vectors that are biting either outdoors or indoors at times when people are not protected by the primary control tools. Additionally, resistance of mosquitoes to these insecticides exacerbates the risk for malaria transmission. Therefore, understanding the degree of endophagy/exophagy of the vectors, when or where humans are exposed to mosquito bites, entry points for malaria vectors into houses and biological factors enhancing malaria transmission in a region is important. The collective information from studying these natural behavioural aspects of mosquitoes will help in designing interventions that protect individuals from infective mosquito bites, thereby reducing malaria transmission and disease burden. The research described in this thesis focused on the biting behaviour of malaria vectors in and around houses in southern Malawi. Chapter 2 provides an overview of the biting times of malaria vectors in Africa, both historically and currently. Our literature search showed that the bi