Can permethrin impregnated clothing protect foresters from ticks?

Introduction
Employees in forestry have a higher risk of contracting infections carried by vectors like ticks. As for some severe infections, no vaccination is available, the prevention of the pathogen transmission plays a major role in primary prevention. The aim of this study was to evaluate if work trousers that are impregnated with the acaricide permethrin have a higher protective effect against ticks than non-impregnated work trousers.

Methods
In a field study, 48 foresters were fitted with permethrin impregnated work trousers (test group) and 36 foresters with conventional non-impregnated work trousers (control group). They documented number and location of ticks via questionnaires after work shifts on at most 16 days in a 4 month period. The protective effect of the impregnated clothing has been examined by an OLS regression, analyzing the association between relative tick frequency (number of ticks / number of sent questionnaires per person) and affiliation to test or control group.

Results
By the time of analysis, 547 respectively 359 questionnaires of foresters in the test group respectively in the control group were received. Altogether 129 ticks were found. The means of individual relative tick frequency were 0.09 respectively 0.27 for the test and the control group considering the whole body and 0.04 respectively 0.13 considering only the legs. For the whole body, a significant decrease of tick affection in the test group was found (B= 0.18; p=0.003).

Discussion
The interim analysis points to a better tick protection in the test group. The permethrin impregnated work trousers reduced the tick affection by a factor of about 3, but could not even in the leg area avert it completely. Permethrin impregnated trousers can be an additional measure in protection against ticks in case the harmlessness for human health is proven.