Acknowledgements

incidence in children <5 years of age decreased also (56% reduction of clinical attacks) compared to a control group having no nets [126]. This was the first clear-cut evidence of ITNs continuing to provide effective personal protection against malaria in an area with a high frequency of kdr in the vector populations. However, absence of a physical barrier in the control group might have overestimated the impact of PY-treated nets against kdr mosquitoes in this study. In southern Benin, a randomised controlled trial was carried out in a mesoendemic area to assess the impact of LLINs scale-up on malaria morbidity in children <5 years of age [127]. In this area, where the kdr frequency is around 50–60% in An. gambiae s.s., transmission increased during the rainy season but was not followed by a seasonal variation in parasite infection and clinical incidence. The evidence is clear that implementation of vector control tools (ITNs and/or IRS) has significantly decreased malaria incidence and parasite infection prevalence in children in endemic countries across Africa, despite moderate-to-high

PY resistance observed in local malaria vectors.

162 Towards Malaria Elimination - A Leap Forward

5. Behavioural resistance to insecticides used in public health

shown that both genetic and environmental factors play a key role [135, 136].

Insecticide resistance is undoubtedly a major challenge to the control of malaria vectors worldwide as it limits the tools available to achieve the goal of controlling and eliminating this

6. Conclusion and perspectives

As we have mentioned previously, the extraordinary success of malaria reduction in Africa is largely due the use of insecticides applied indoors through LLINs and IRS [6]. This malaria control approach takes advantage of the strong human preference, as well as the indoor feeding and resting behaviour of African malaria-transmitting mosquitoes [128]. As we have shown in this chapter, progress has been made in understanding the genetic basis of the ability of mosquitoes to survive insecticide entering the body. However, little is known about the causes of increasingly reported changes in blood-feeding behaviour developed by certain species of malaria-transmitting mosquitoes to avoid exposure to insecticides [7]. This phenomenon is known as behavioural resistance and it is defined as any modification in insect behaviour that helps to circumvent the lethal effects of insecticides. Thus, through intraspecific behavioural shifts in biting time, location and host preference, malaria-transmitting mosquitoes avoid exposure to insecticides, feeding on humans when most people are not protected [129], jeopardising the current control strategy in Africa primarily based on indoor application of insecticides [130–132]. Recent studies conducted in West and East Africa have shown that indoor application of insecticides may induce intraspecific behavioural shifts towards early biting, exophagic biting and exophilic resting behaviour in malaria-transmitting mosquitoes [130, 131, 133]. Similarly, current studies conducted in Central Africa showed a comparable shift towards exophilic resting behaviour [134]. Mathematical modelling and field evidences have proved that these shifts in blood-feeding behaviour could threaten and impact on the current control programmes [132, 135]. The mechanisms driving these shifts have not yet been elucidated, although some studies have

This work was supported by a Wellcome Trust Senior Fellowship in Biomedical Sciences (WT101893MA) to CSW.
