Spatial repellency of transfluthrin-treated hessian strips against laboratory-reared Anopheles arabiensis mosquitoes in a semi-field tunnel cage

Sheila B Ogoma, Hassan Ngonyani, Emmanuel T Simfukwe, Anthony Mseka, Jason Moore, Gerry F Killeen, Sheila B Ogoma, Hassan Ngonyani, Emmanuel T Simfukwe, Anthony Mseka, Jason Moore, Gerry F Killeen

Abstract

Background: Vapour phase spatial repellents deter mosquitoes from attacking one or more humans in a protected space. Simulation models indicate that high coverage of spatial repellents can enhance the impact of long - lasting insecticide nets (LLINs) and indoor residual spraying (IRS) where mosquito vectors commonly bite humans outdoors. Here we report a preliminary evaluation of an effective, user-friendly prototype product for delivering spatial repellents to protect against malaria vector mosquitoes.

Findings: Protective efficacy of a 4.0 × 0.3 m strip of hessian sacking treated with 10 ml of transfluthrin was evaluated in a 60 m × 2 m × 2.5 m netting tunnel with malaria-free insectary-reared Anopheles arabiensis Patton mosquitoes. Personal protection, in terms of proportional reduction of exposure to bites, was measured by comparing human landing catches of volunteers with treated and untreated strips. A freshly treated hessian strip reduced mosquito attack rate on human volunteers by > 99% and consistently conferred > 90% protective efficacy for a period of 6 months. Over the entire study period, only 22 out of 1400 released mosquitoes bit volunteers using the treated sacking strip while 894 out of 1400 mosquitoes released into cages containing volunteers using an untreated strip fed upon them.

Conclusion: Locally available natural fibers may be promising absorbent substrates for delivering spatial repellents, such as transfluthrin, to protect against mosquitoes in tropical settings. However, these observations relate to a single prototype specimen of this particular device, therefore, much more detailed, well replicated studies are essential to establish long-term efficacy, effectiveness, practicability and affordability.

Figures

Figure 1
Figure 1
Transfluthrin hessian strip. The hessian strip is made from fine sisal fiber woven together to make sacking fabric. The strip is 4 × 0.3 m long. It is treated with transfluthrin. The strip is suspended on 4 wooden poles making approximately 1 m2 area surrounding the human participant conducting mosquito catches.
Figure 2
Figure 2
The number of mosquitoes recovered by human landing catches with transfluthrin and untreated strips. A graph comparing the number of mosquitoes recovered by human landing catches during rounds of experiments with transfluthrin treated and untreated strips during six months. The graph indicates a reduction in the number of bites occurring on a human participant who had a treated strip compared to one with an untreated strip. Each data point represents a single release of mosquitoes in a single experimental unit with either a treated or untreated strip of hessian sacking.

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