Abstract
BackgroundTicks of the species Ixodes ricinus are the main vectors of Lyme Borreliosis and Tick-borne Encephalitis – two rapidly emerging diseases in Europe. Repellents provide a practical means of protection against tick bites and can therefore minimize the transmission of tick-borne diseases. We developed and tested seven different dodecanoic acid (DDA)-formulations for their efficacy in repelling host-seeking nymphs of I. ricinus by laboratory screening. The ultimately selected formulation was then used for comparative investigations of commercially available tick repellents in humans.MethodsLaboratory screening tests were performed using the Moving-object (MO) bioassay. All test formulations contained 10% of the naturally occurring active substance DDA and differed only in terms of the quantitative and qualitative composition of inactive ingredients and fragrances. The test procedure used in the human bioassays is a modification of an assay described by the U.S. Environmental Protection Agency and recommended for regulatory affairs. Repellency was computed using the equation: R = 100 - NR/N × 100, where NR is the number of non-repelled ticks, and N is the respective number of control ticks. All investigations were conducted in a controlled laboratory environment offering standardized test conditions.ResultsAll test formulations strongly repelled nymphs of I. ricinus (100-81% protection) as shown by the MO-bioassay. The majority of ticks dropped off the treated surface of the heated rotating drum that served as the attractant (1 mg/cm2 repellent applied). The 10% DDA-based formulation, that produced the best results in laboratory screening, was as effective as the coconut oil-based reference product. The mean protection time of both preparations was generally similar and averaged 8 hours.Repellency investigations in humans showed that the most effective 10% DDA-based formulation (~1.67 mg/cm2 applied) strongly avoided the attachment of I. ricinus nymphs and adults for at least 6 hours. The test repellent always provided protection (83-63%) against I. ricinus nymphs equivalent to the natural coconut oil based reference product and a better protection (88-75%) against adult ticks than the synthetic Icaridin-containing reference repellent.ConclusionWe found that the 10% DDA-based formulation (ContraZeck®) is an easily applied and very effective natural repellent against I. ricinus ticks. By reducing the human-vector contact the product minimises the risk of transmission of tick-borne diseases in humans.
Highlights
Ticks of the species Ixodes ricinus are the main vectors of Lyme Borreliosis and Tick-borne Encephalitis – two rapidly emerging diseases in Europe
We found that the 10% dodecanoic acid (DDA)-based formulation (ContraZeck®) is an applied and very effective natural repellent against I. ricinus ticks
The most important and commonly found tick in northern Europe is Ixodes ricinus (L.), which acts as a vector of e.g. several Borrelia species causing Lyme Borreliosis, and of the Tick-borne Encephalitis (TBE) virus [1]
Summary
Ticks of the species Ixodes ricinus are the main vectors of Lyme Borreliosis and Tick-borne Encephalitis – two rapidly emerging diseases in Europe. The most important and commonly found tick in northern Europe is Ixodes ricinus (L.), which acts as a vector of e.g. several Borrelia species causing Lyme Borreliosis, and of the Tick-borne Encephalitis (TBE) virus [1]. Since certain tick-borne pathogens, like the TBE virus, are transmitted to the host during the initial minutes of tick feeding [20], it is important to prevent tick bites completely. Tick-borne encephalitis is an endemic disease that is generally limited to certain geographic foci [2,3]. Thirty per cent of humans bitten by an infected tick develop symptoms of TBE (headache, fever, nausea) [1,2].
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