Abstract
BackgroundMosquito behavior assays have been used to evaluate the efficacy of vector control interventions to include spatial repellents (SR). Current analytical methods are not optimized to determine short duration concentrations of SR active ingredients (AI) in air spaces during entomological evaluations. The aim of this study was to expand on our previous research to further validate a novel air sampling method to detect and quantitate airborne concentrations of a SR under laboratory and field conditions.Methodology/Principal FindingsA thermal desorption (TD) gas chromatography-mass spectrometry (GC-MS) method was used to determine the amount of dichlorodiphenyltrichloroethane (DDT) in samples of air. During laboratory experiments, 1 L volumes of air were collected over 10 min intervals from a three-chamber mosquito behavior assay system. Significantly higher levels of airborne DDT were measured in the chamber containing textiles treated with DDT compared to chambers free of AI. In the field, 57 samples of air were collected from experimental huts with and without DDT for onsite analysis. Airborne DDT was detected in samples collected from treated huts. The mean DDT air concentrations in these two huts over a period of four days with variable ambient temperature were 0.74 µg/m3 (n = 17; SD = 0.45) and 1.42 µg/m3 (n = 30; SD = 0.96).Conclusions/SignificanceThe results from laboratory experiments confirmed that significantly different DDT exposure conditions existed in the three-chamber system establishing a chemical gradient to evaluate mosquito deterrency. The TD GC-MS method addresses a need to measure short-term (<1 h) SR concentrations in small volume (<100 L) samples of air and should be considered for standard evaluation of airborne AI levels in mosquito behavior assay systems. Future studies include the use of TD GC-MS to measure other semi-volatile vector control compounds.
Highlights
Mosquitoes are capable of transmitting numerous diseases including malaria, dengue fever, yellow fever, Japanese encephalitis, and West Nile fever among others [1,2]
Inter-day variance was assessed to determine the effect of sample preparation and time (Fig. 3)
Standard environmental sampling methods were not designed to measure airborne active ingredients (AI) in samples collected during 10–60 min intervals used in the mosquito behavior assays evaluated in this report
Summary
Mosquitoes are capable of transmitting numerous diseases including malaria, dengue fever, yellow fever, Japanese encephalitis, and West Nile fever among others [1,2]. Due to the geographic distribution of mosquitoes, as many as three billion people are at risk of infection with at least one mosquito-borne disease [3,4]. Of those at risk, malaria causes the highest burden of disease with an estimated 216 million cases and 655,000 deaths reported in 2012 [3]. Two of the primary strategies to control mosquito-borne diseases as recommended by the World Health Organization (WHO) are the use of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) to reduce exposure to mosquitoes [6,7]. Current analytical methods are not optimized to determine short duration concentrations of SR active ingredients (AI) in air spaces during entomological evaluations. The aim of this study was to expand on our previous research to further validate a novel air sampling method to detect and quantitate airborne concentrations of a SR under laboratory and field conditions
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