Reduced effectiveness of permethrin-treated military uniforms after prolonged wear measured by contact irritancy and toxicity bioassays with Ixodes scapularis (Acari: Ixodidae) nymphs.

Factory-treated permethrin uniforms are the primary method used by the US Army to prevent arthropod bites and transmission of arthropod-borne diseases. In this study previously worn uniforms were collected from cadets at the United States Military Academy in West Point, NY to determine the amount of permethrin remaining after prolonged wear and subsequent effects on ticks. Six trousers were collected from cadets in the sophomore, junior, and senior classes. A new, unwashed uniform served as a positive control and an untreated maternity uniform served as a negative control. Fabric samples were removed from each trouser and used in bioassays with laboratory-reared Ixodes scapularis Say nymphs. Contact irritancy bioassays measured the nymphs' ability to remain in contact with fabric for a period of 5 min. Toxicity bioassays measured tick survival at 1 and 24 h after contacting uniform samples. liquid chromatography-mass spectrometry was used to quantify the permethrin content (mg/cm2) in each uniform after the bioassays were complete. The results showed significant amounts of permethrin were lost after extended wear and it was related to the cadet year group. The contact irritancy assays found uniforms with less permethrin did not irritate ticks and cause them to dislodge. Mortality was also affected by permethrin levels, with less ticks dying at 24 h on older uniforms. The results from this study show older uniforms lose most of their permethrin and no longer provide the same levels of protection.