Outdoor mosquito control using odour-baited devices: development and evaluation of a potential new strategy to complement indoor malaria prevention methods

Existing malaria vector control measures, such as long lasting insecticide treated nets (LLINs) and house spraying with residual insecticides (IRS), have significantly contributed to the decreasing burden of malaria in sub-Saharan Africa [1]. It is estimated that intervention scale-up from the year 2000 to 2010 averted between 563.000 and 1.36 million child deaths in 43 malaria-endemic countries in Africa [2]. Despite these gains, evidence suggests that even in communities where most people already use the current prevention measures, there remains a significant amount of residual transmission, not readily amenable to control [3-5]. For example, while LLINs and IRS are especially effective against indoor-feeding and indoor-biting species such as Anopheles gambiae and An. funestus, these interventions are far less effective against An. arabiensis [5,6], which now dominates many epidemiological niches left by An. gambiae after long-term vector control in endemic countries [4,5,7-10]. Others include An. rivulorum and An. ziemanni, which also play a secondary but vital transmission role in areas with high IRS and LLIN use [11 -13]. This situation constitutes a major long-term challenge to the goal of malaria elimination and eventual eradication [14,15], especially where vector species have divergent ecological needs [16], or reduced behavioural susceptibility to indoor insecticidal interventions [17,18]. Even if universal population coverage with LLINs and IRS was to be achieved, as prescribed by the Global Malaria Action Plan (GMAP) [19], Anopheles mosquitoes would still have numerous resources upon which they could survive and potentially transmit disease, albeit at low levels [16, 20]. Moreover, while most malaria transmission in Africa still occurs indoors [21,22], outdoor biting is increasing in both urban and rural settings [7,23,24]. It is therefore reasonable to infer that despite the remarkable successes of the ongoing malaria prevention operations, efforts towards elimination will likely fall short unless complementary strategies are initiated to target disease-transmitting mosquitoes outdoors [15,16,25]. The Outdoor Mosquito Control (OMC) project, at the Ifakara Health Institute (IHI) in Tanzania, is one example of a handful of ongoing studies around the world that address these challenges. The aim of the OMC project at IHI is to develop and test an integrated outdoor mosquito control strategy that can be sustainably used to complement LLINs and IRS and therefore accelerate malaria elimination efforts in sub-Sahara Africa. This article outlines the idea behind this project, and provides an overview of major research activities conducted by the team. It also reviews some important early findings of the project and discusses the overall potential of this strategy in the context of the malaria control and elimination agenda.