Evaluation of standard field and laboratory methods to compare protection times of the topical repellents PMD and DEET

Barbara Colucci,Pie Müller

doi:10.1038/s41598-018-30998-2

Barbara Colucci, Pie Müller

Open Access

https://doi.org/10.1038/s41598-018-30998-2

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Abstract

Mosquitoes are important vectors of pathogens, and travellers to disease endemic countries are advised to avoid bites by applying topical repellents. Topical repellents are typically tested either in the arm-in-cage (AIC) test under laboratory conditions or in the field, but not often under both conditions. We, therefore, investigated how two topical repellents, 15% para-menthane-3,8-diol (PMD) and 15% N,N-diethyl-3-methylbenzamide (DEET) compare against each other both in the AIC test against three species recommended by the World Health Organization (i.e. Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus) and at two field sites in Switzerland, while using the same study participants in all experiments. In the field, the median complete protection time (CPT) was at least 6 hours for both PMD and DEET, while in the AIC test DEET slightly outperformed PMD. CPTs for DEET in the AIC test were 0.5, 2 and 2 hours against Ae. aegypti, An. stephensi and Cx. quinquefasciatus, respectively, and the corresponding median CPTs for PMD were 0.5, 1 and 0.5 hours. In conclusion, DEET slightly outperformed PMD in the AIC test, while the observed landing rates suggest the AIC test to underestimate efficacy of topical repellents in areas with lower landing pressure.

Highlights

Biting mosquitoes (Diptera, Culicidae) are important vectors of several diseases such as malaria, filariasis and arboviral infections, including dengue, West-Nile, chikungunya and Zika, mainly in the tropical and subtropical regions and increasingly in Europe as recent autochthonous cases of dengue and chikungunya have shown[1,2,3,4]
For the field experiments in the Thurauen Nature Reserve, one measurement is missing for 15% PMD and one for the negative control due to two study participants being on sick leave
227 landings were recorded in the field experiments using human landing catch (HLC) with an approximately equal number of mosquitoes counted in the Langholz forest (n = 115) and the Thurauen Nature Reserve (n = 112)

Summary

Introduction

Biting mosquitoes (Diptera, Culicidae) are important vectors of several diseases such as malaria, filariasis and arboviral infections, including dengue, West-Nile, chikungunya and Zika, mainly in the tropical and subtropical regions and increasingly in Europe as recent autochthonous cases of dengue and chikungunya have shown[1,2,3,4]. The most widely used active ingredient in commercially available mosquito repellents is the synthetic compound N,N-diethyl-3-methylbenzamide (DEET) which is generally regarded as the “gold standard” due to its high efficacy against a broad range of insects[10,11]. Several studies have compared the efficacy of PMD against DEET, yet the existing data are somewhat difficult to read because the formulations tested were either commercially available products, containing additional compounds that potentially influence the efficacy of the repellent[15], or the concentrations of PMD and DEET of the formulations applied within the same study differed[16,17], or both[14,15,18,19]. In the AIC test, according to the guidelines, a forearm of a study participant is treated with a defined amount of the repellent formulation (e.g. 1 ml per 600 cm[2]). Similar endpoints may be determined on the basis of mosquitoes landing or biting on an exposed skin area, usually the lower leg, while the mosquitoes are collected by aspiration allowing for the identification of the mosquito species in a laboratory

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Conclusion