Permethrin-treated clothing as protection against the dengue vector, Aedes aegypti: extent and duration of protection

Background: 3900 million people globally are at risk of dengue fever infection, with its distribution increasing rapidly over the past 50 years. Since the primary vector, Aedes aegypti, is exophilic and most active during the day, personal protection technologies, such as insecticide treated clothing, could provide significant protection from mosquito bites. Methods: World Health Organisation Pesticide Evaluation Scheme (WHOPES) cone and arm-in-cage assays were used to assess protection, knockdown and mortality against factory, home-dipped and microencapsulated permethrin-treated fabrics using Ae. aegypti mosquitoes. Factory-treated clothing was then analysed further to investigate the effects of insecticide resistance, clothing coverage, washing, Ultra-violet light and ironing. Results: Factory-treated clothing showed the greatest protective effect (1 h KD 96.5% and 24 h mortality 97.1%), landing protection (59% (95% CI = 49.2–66.9) and bite protection (100%). Landing and biting protection reduced significantly from 58.9% to 18.5% and 28.6% to 11.1% after 10 washes for simulated hand washing. Resistance to permethrin had no effect on the efficacy of the clothing, with coverage playing an important role. Full coverage provided the highest protection (79.4% landing protection, 100% biting protection). Free flight room assays showed no difference in landing protection between the two coverage types but bite protection was significantly greater (>90%) with full coverage. HPLC confirmed ironing reduced permethrin content after 1 week simulated use, with a 96.7% decrease after 3 months. UV exposure was shown to have no effect. Conclusion: Insecticide treated clothing can provide significant biting and landing protection, even in a resistant strain. However, our findings also suggest that clothing may provide only short-term protection due to the effect of washing and ironing, highlighting the need for improved clothing treatment techniques. Disclosure: Nothing to disclose.