The Mode of Action of Spatial Repellents and Their Impact on Vectorial Capacity of Anopheles gambiae sensu stricto

Abstract

Malaria vector control relies on toxicity of insecticides used in long lasting insecticide treated nets and indoor residual spraying. This is despite evidence that sub–lethal insecticides reduce human–vector contact and malaria transmission. The impact of sub–lethal insecticides on host seeking and blood feeding of mosquitoes was measured. Taxis boxes distinguished between repellency and attraction inhibition of mosquitoes by measuring response of mosquitoes towards or away from Transfluthrin coils and humans. Protective effective distance of coils and long-term effects on blood feeding were measured in the semi–field tunnel and in a Peet Grady chamber. Laboratory reared pyrethroid susceptible Anopheles gambiae sensu stricto mosquitoes were used. In the taxis boxes, a higher proportion of mosquitoes (67%–82%) were activated and flew towards the human in the presence of Transfluthrin coils. Coils did not hinder attraction of mosquitoes to the human. In the semi–field Tunnel, coils placed 0.3 m from the human reduced feeding by 86% (95% CI [0.66; 0.95]) when used as a “bubble” compared to 65% (95% CI [0.51; 0.76]) when used as a “point source”. Mosquitoes exposed to coils inside a Peet Grady chamber were delayed from feeding normally for 12 hours but there was no effect on free flying and caged mosquitoes exposed in the semi–field tunnel. These findings indicate that airborne pyrethroids minimize human–vector contact through reduced and delayed blood feeding. This information is useful for the development of target product profiles of spatial repellent products that can be used to complement mainstream malaria vector control tools.

A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria

“…These observations are consistent with recent studies showing that, transfluthrin incapacitates mosquitoes by inhibiting blood feeding [35], rather than repelling them in the strict sense [33,36]. Furthermore, transfluthrin can also kill mosquitoes that closely approach protected humans [6], which would also preclude diversion to unprotected individuals nearby.…”

“…Furthermore, transfluthrin can also kill mosquitoes that closely approach protected humans [6], which would also preclude diversion to unprotected individuals nearby. Transfluthrin-treated hessian emanators may therefore be far safer for nearby non-users than conventional topical repellents like N,N-Diethyl-meta-toluamide (DEET) [11,34] and might even provide area-wide protection of users and non-users alike, similarly to LLINs and IRS [12,35]. Given the limited number of tools available for protecting against outdoor-biting mosquitoes, and the limited durability of existing repellent products, the observed reduction of biting exposure by more than three quarters over a period of almost a full year, without retreating the strips, is both unprecedented and encouraging.…”

Using evolution to generate sustainable malaria control with spatial repellents

“…However, it is increasingly being acknowledged that a switch away from indoor biting, by reducing vector fitness and/or by creating a less favourable context for transmission, may offer public health benefits as an end in itself, consistent with the idea that the efficacy of DDT may be partly derived from its repellent rather than solely its toxic effects (Roberts et al, 2000; Roberts, 1993; Grieco et al, 2000). The use of spatial repellents as a tool to maintain vector-free homes is therefore now being actively investigated as a means of reducing transmission of malaria and dengue (Achee et al, 2012; N'Guessan et al, 2006; Ogoma et al, 2014; University of Notre Dame, 2016). This can be viewed as an alternative means to achieve the same benefits as the application of physical barriers to prevent vector access to homes (Roll Back Malaria, 2015; Patrick, 1900; Menger et al, 2016).…”

Spatial repellency and other effects of transfluthrin and linalool on Aedes aegypti and Aedes albopictus

“…albopictus the transfluthrin concentration of 10% obtained the best attraction percentage of 52.5 ± 3.85%, with a SAI of ‐0.24 ± 0.08. These results can be compared with the results presented by Ogoma et al () on the response of Anopheles gambiae (ss) exposed to coils of transfluthrin (0.03, 0.015, and 0.0045%), where the proportion of actívated mosquitoes depended on the concentration. At the highest concentration, 82% of the mosquitoes left the central treatment chamber when the coil was placed near the human bait.…”