Abstract
BackgroundBefore topical repellents can be employed as interventions against arthropod bites, their efficacy must be established. Currently, laboratory or field tests, using human volunteers, are the main methods used for assessing the efficacy of topical repellents. However, laboratory tests are not representative of real life conditions under which repellents are used and field-testing potentially exposes human volunteers to disease. There is, therefore, a need to develop methods to test efficacy of repellents under real life conditions while minimizing volunteer exposure to disease.MethodsA lotion-based, 15% N, N-Diethyl-3-methylbenzamide (DEET) repellent and 15% DEET in ethanol were compared to a placebo lotion in a 200 sq m (10 m × 20 m) semi-field system (SFS) against laboratory-reared Anopheles arabiensis mosquitoes and in full field settings against wild malaria vectors and nuisance-biting mosquitoes. The average percentage protection against biting mosquitoes over four hours in the SFS and field setting was determined. A Poisson regression model was then used to determine relative risk of being bitten when wearing either of these repellents compared to the placebo.ResultsAverage percentage protection of the lotion-based 15% DEET repellent after four hours of mosquito collection was 82.13% (95% CI 75.94-88.82) in the semi-field experiments and 85.10% (95% CI 78.97-91.70) in the field experiments. Average percentage protection of 15% DEET in ethanol after four hours was 71.29% (CI 61.77-82.28) in the semi-field system and 88.24% (84.45-92.20) in the field.ConclusionsSemi-field evaluation results were comparable to full-field evaluations, indicating that such systems could be satisfactorily used in measuring efficacy of topically applied mosquito repellents, thereby avoiding risks of exposure to mosquito-borne pathogens, associated with field testing.
Highlights
Before topical repellents can be employed as interventions against arthropod bites, their efficacy must be established
Poisson regression analysis The relative risk of being bitten by a mosquito over the four hour test when using 15% DEET lotion compared to placebo lotion was reduced by 91.8%
When 15% DEET ethanol was compared to the placebo lotion, the relative risk of being bitten by mosquitoes was reduced by 92.30% (Table 1)
Summary
Before topical repellents can be employed as interventions against arthropod bites, their efficacy must be established. There is, a need to develop methods to test efficacy of repellents under real life conditions while minimizing volunteer exposure to disease. There is a need to develop methods to test efficacy of repellents under representative user conditions while minimizing volunteer exposure to vector-borne diseases. There are several techniques that have been proposed for testing topical repellents while reducing human exposure to mosquito bites These options include: 1) use of synthetic mosquito attractants that mimic human volunteers [7]; 2) use of animals instead of human volunteers [8,9]; 3) use of in vitro blood feeding membrane [10,11,12]; 4) In vitro olfactometry [13]; and, 5) use of a semi-field system (SFS) [14,15]. This study examined whether tests carried out in a SFS would yield comparable results to tests conducted in field setting
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