Protective efficacy of permethrin-treated trousers against tick infestation in forestry workers

Introduction and objective. Prevention of tick borne diseases in forestry workers is essentially based on the use of appropriate clothing. The objective of this pragmatic, randomized, controlled trial was to assess the potential benefit of permethrin-treated working trousers for the prevention of tick infestation during forestry work. Materials and methods. N=164 male forestry workers were equipped for a period of 16 weeks with permethrin-treated (intervention group - I) or untreated work trousers (control group II). Subgroups, according to the use of trousers with (I-1, II-1) or without cut protection lining (I-2,II-2) were constituted. Tick infestation (quantity of ticks on the body surface) was assessed by questionnaire after 16 workdays. Control and intervention groups were compared by calculating the infestation rate (percentage of subjects with ticks) and the average number of ticks per workday. Results. The infestation rate in the intervention group was significantly lower than in the control group (36.6 vs. 63.4%, p=0.001; Fisher-test). Further analysis revealed a significant reduction of tick infestation by permethrin treatment only for subjects wearing trousers without the cut protection lining (I-2: 34.2 vs. II-2: 80.0%, p<0.001), while users of cut protection trousers did not benefit from such treated trousers (I-1: 38.6 vs. II-1:47.6%, n.s.). Similar results were found for comparisons based on the average number of ticks per workday. Conclusions. The use of permethrin-treated trousers does not completely prevent tick infestations. Improvement of tick protection has been shown only for some applications, but not in general. Additional prevention measures are therefore still indispensable.