Spatial repellents: from discovery and development to evidence-based validation

Abstract

International public health workers are challenged by a burden of arthropod-borne disease that remains elevated despite best efforts in control programmes. With this challenge comes the opportunity to develop novel vector control paradigms to guide product development and programme implementation. The role of vector behaviour modification in disease control was first highlighted several decades ago but has received limited attention within the public health community. This paper presents current evidence highlighting the value of sub-lethal agents, specifically spatial repellents, and their use in global health, and identifies the primary challenges towards establishing a clearly defined and recommended role for spatial repellent products in disease control.

Absence of Close-Range Excitorepellent Effects in Malaria Mosquitoes Exposed to Deltamethrin-Treated Bed Nets

“…50 The wind tunnel assay is more sensitive to reveal behavioral effects than the current WHO assays and could be considered as an additional method useful for investigating spatial repellent effects of current and new insecticidal compounds. 51 In the wind tunnel setup, in the presence of human host cues, it was found that both susceptible and resistant An. gambiae s.s. mosquitoes never spent as much as 3 minutes (cumulatively) on the test netting material in the absence of a bloodmeal.…”

Impact of a Spatial Repellent on Malaria Incidence in Two Villages in Sumba, Indonesia

“…These actions are dose-dependent and include vapor phase repellency (at concentrations below toxic thresholds) and vapor phase toxicity (at higher doses). Although the current protocol could not differentiate the contribution of these two actions to the success of reduced HLC, we are confident that the concentration encountered in the house was well below the toxic level for metofluthrin based on air sampling conducted inside and outdoors of experimental huts using same dose metofluthrin coils 4 . Nevertheless, this remains a critical missing piece of the equation and will require a more detailed, integrated investigative approach involving other tools such as laboratory-based excito-repellency assays (e.g., HITSS) and field-based experimental huts (e.g., entry and exit traps).…”

“…Such evidence of human health impact is a fundamental and essential component in the critical path of development of any vector control tool, [38][39][40][41] especially new paradigms such as SR. 4 If the crude estimate of protective efficacy shown here, about 52%, is verified in statistically robust cluster-randomized trials, this instrument of control would likely approximate that benefit associated with LLINs. 42 It is important to note this study was not intended to assess a practical method of delivery of a spatial repellent product in malaria control.…”

“…Of importance, there is a reduced probability of creating a survival advantage with either behavioral or physiological resistance to the agent inducing this effect. 4 Spatial repellency as a means of prevention was considered more than 60 years ago but never seriously pursued. Development algorithms for chemicals aimed against mosquitoes have focused upon mortality effects for setting thresholds of efficacy, and, indeed, SR properties were considered disadvantageous (compromising contact and mortality).…”

“…parasite. Modifying vector behavior through the chemical action of spatial repellency (SR) 4 is one such approach. Here, we define SR as the ability of airborne chemicals to reduce human vector contact by eliciting one or more insect behaviors.…”