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

Objective To evaluate the residual insecticidal activity of the PermaNet^® 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^® 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® curtains remains high after 12 months use under field conditions.