Essential oils as tick repellents on clothing

Oliver Soutar,Freya Cohen,Richard Wall

doi:10.1007/s10493-019-00422-z

Abstract

Essential oils show promise as natural alternatives to synthetic tick repellents, but few studies have investigated their repellent efficacy in vivo or under field conditions. Here, blanket-drags and standardised walks were employed to evaluate tick acquisition by 1 m2 cotton blankets or cotton trousers, respectively, in woodland edge habitats of known high tick abundance. Blankets and trousers had been treated with one of 5% oregano, rosemary, spearmint or thyme oils, 20% DEET (N,N-diethyl-3-methylbenzamide) (positive control) or ethanol excipient-only (negative control). The number of ticks present on the blankets or trousers differed significantly between treatments: spearmint oil treatments resulted in significantly fewer ticks than the negative controls for both blankets and trousers and significantly fewer ticks were present on the oregano oil treated blankets. For ticks that did attach to the trousers, the rate of drop off within 3 min was significantly higher for trousers treated with spearmint oil or thyme oil than ethanol, oregano oil and rosemary oil. No reduction in repellence was detected over a 24 h period between treatment and testing. The results suggest that 5% oregano and spearmint oils exhibit potential as natural clothing repellents, with an effective equivalence to 20% DEET.

Highlights

Ticks act as vectors of a greater diversity of disease-causing pathogens of humans than any other arthropod (Ginsberg and Faulde 2008)
1385 ticks were found on blankets immediately following blanket-drags, with a median per drag of 5.5 for DEET (n = 18), 29 (IQR: 24.25) for ethanol (n = 18), 4 (IQR: 7) for oregano oil (n = 17), 11 (IQR: 28) for rosemary oil (n = 17), 2 (IQR: 5) for spearmint oil (n = 18), and 5 (IQR: 7.25) for thyme oil (n = 18) (Fig. 1a)
There was a significant difference between treatments in the number of ticks counted on blankets ( (25) = 26.16, P < 0.001), with post hoc tests showing that significantly more ticks were found on blankets treated with ethanol only than those treated with DEET (P = 0.008), oregano oil (P = 0.010), or spearmint oil (P < 0.001)

Summary

Introduction

Ticks act as vectors of a greater diversity of disease-causing pathogens of humans than any other arthropod (Ginsberg and Faulde 2008). In Europe, it is the vector of Borrelia burgdorferi s.l., the causal agent of Lyme disease, and tick-borne encephalitis, which respectively infect more than 100,000 and 3000 people annually (Pålsson et al 2008). The development of more effective personal protection measures against tick attachment and biting would make an important contribution to reducing the incidence of tick-borne disease. Arthropod repellents are an effective means for humans to protect themselves against tick bites (Piesman and Eisen 2008; Bissinger and Roe 2010; Pages et al 2014). The majority of commercially-available tick repellents are synthetic molecules, of which DEET (N,N-diethyl-3-methylbenzamide) is the most extensively used active ingredient (Bissinger and Roe 2010; Pages et al 2014). Biologically-based repellents, the plant-derived essential oils, may constitute an appealing alternative (Bissinger and Roe 2010; Del Fabbro and Nazzi 2013; Benelli et al 2016, 2018)

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