Residual insecticidal activity of long-lasting deltamethrin-treated curtains after 1 year of household use for dengue control

To evaluate the residual insecticidal activity of the PermaNet (R) curtains on Aedes aegypti after 1 year of use in Thai households and to assess the influence of sun and dust exposure, washing practices and detergent use.Methods: We sampled UV-protected PermaNet (R) curtains made of a long-lasting deltamethrin-[55 mg/m2] treated polyester netting, before (10 curtains) and after 8 (10 curtains) and 12 months (66 curtains) of household use in a field site in Chon Buri, Thailand. We assessed the residual insecticidal activity of the curtains by standard WHO bioassay, using a deltamethrin-susceptible insectarium Aedes aegypti strain.Results: Mosquito mortality was 100% before distribution, 100% at 8 months and 98.2% (95% CI 97.9-98.5) at 12 months of use. Sunlight, hand-washing and detergent use had no effect on the residual insecticidal activity after 12 months. However, the mosquito survival rate increased by a factor of 6.4 (95% CI 3.5-11.8) on machine-washed curtains and by a factor of 2.0 (95% CI 1.4-2.9) on curtains not covered by dust.Conclusion: The residual insecticidal activity of PermaNet (R) curtains remains high after 12 months use under field conditions.