Evaluating ATSBs for Malaria Reduction in Kenya

Overview

The effectiveness of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) in western Kenya are threatened by insecticide resistance and vector behaviour changes toward early evening and outdoor biting malaria vectors. New tools to control malaria are needed to reduce and even interrupt malaria transmission. Attractive Targeted Sugar Bait (ATSB) is a promising new intervention designed to attract and kill mosquitoes, including those that IRS and LLINs do not effectively target. The ATSB 'bait stations' are A4-sized panels containing thickened fruit syrup laced with a neonicotinoid insecticide, dinotefuran, to attract and kill the foraging vectors. Entomological field trials in western Mali showed that ATSBs successfully reduce mosquito densities and longevity and thus have the potential to reduce malaria transmission. In Kenya, the investigators will conduct an open-label cluster-randomized controlled trial in 80 village clusters (40 per arm) to evaluate the effect of ATSBs on the burden of malaria. During two years, households in half of these village clusters will receive two or three ATSB bait stations per household structure on exterior walls approximately 1.8 meters above the ground. ATSBs will be replaced every six months. The primary outcome will be the incidence of clinical malaria in children aged 1-\<15 years enrolled in a prospective cohort followed monthly for about six months each during a 2-year period. Secondary outcomes include malaria infection prevalence assessed by rapid diagnostic tests through household surveys and the case burden of clinical malaria assessed by passive facility-based and community-based surveillance. The study includes entomological monitoring and nested acceptability, feasibility, and health economics studies. The stand-alone trial in western Kenya is a part of a multi-country ATSB consortium conducting similar trials in Zambia and Mali.

The current malaria vector control tools, long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are critically important and have saved many lives. However, their effectiveness in western Kenya is threatened by insecticide resistance and vector behaviour changes toward more early evening and outdoor biting malaria vectors. LLINs and IRS specifically target indoor-biting and indoor-resting mosquitoes. Malaria vectors exhibit different behavioural characteristics that mitigate the effectiveness of vector control strategies. For example, traditionally, An. gambiae s.s. has been regarded as human-biting with late-night indoor-feeding and indoor-resting behaviours, while An. Arabiensis is found more often in drier environments and is more zoophagic with outdoor biting and resting behaviours. Following LLINs and IRS's widespread scale-up, the dominant African vectors' distributions and behaviours changed with An. gambiae s.s. and An. Funestus (also an indoor human biter) diminishing in abundance relative to An. arabiensis. Subsequently, shifts towards earlier evening biting by An. Gambiae s.s. (before people enter houses to sleep under LLINs) and later biting by An. Funestus (biting in the morning after sunrise) are examples of behavioural plasticity enabling these species to avoid contact with the LLIN and IRS insecticides. There is a need for interventions that supplement and complement LLINs and IRS by killing mosquitoes outside houses using other biologic mechanisms (e.g., targeting sugar feeding behaviour). Furthermore, insecticides are required with novel modes of action that may restore sensitivity to pyrethroids by killing both pyrethroid-resistant and sensitive mosquitoes. Attractive Targeted Sugar Bait (ATSB) (the name was recently changed from Attractive Toxic Sugar Bait to highlight that it targets malaria vectors) is a promising new intervention that potentially fills the need for outdoor interventions with novel killing effects. ATSB 'bait stations' are A4-sized panels containing thickened fruit syrup laced with a neonicotinoid insecticide (dinotefuran) to attract and kill the foraging vectors. Entomological field trials in Mali showed that ATSBs successfully reduce mosquito densities and longevity and thus have the potential to reduce malaria transmission. Large scale efficacy studies are now needed to establish the efficacy of ATSB for controlling malaria transmission.