Wash resistance of insecticide-treated materials

Abstract

The effectiveness of insecticide-treated materials (ITMs) for malaria control is reduced by washing them. This research in Colombia and Bolivia investigated the resistance of different insecticide formulations and, in particular, a commercially available impregnated bednet (PermaNet) which provides chemical protection for the insecticide. The fabrics studied were all polyester; the pyrethroids used for impregnation were deltamethrin (tablet and suspension concentrate both at 25 mg/m2 target dose), lambdacyhalothrin (capsule suspension at 15 mg/m2; laboratory study only), alphacypermethrin (suspension concentrate at 40 mg/m2) and, in the case of PermaNet, deltamethrin (55 mg/m2). The indicator of wash resistance was Anopheles spp. mortality (using the bioassay cone method) before and after different numbers and intensities of washing. When the fabrics were washed under controlled conditions, gently with water and a bar of soap, the wash resistance of all formulations was good (100% Anopheles mortality after 3 washes). However, when the impregnated nets were soaked for 30-60 min and washed with soap powder and tap water by local women in the usual way, the mortality after 4 washes declined considerably (43.5% and 41.3% for deltamethrin tablets and liquid respectively when washing every second day). Alphacypermethrin showed slightly better results after 3 washes every 7th day compared to deltamethrin tablets (63.8% and 43.3% mortality, respectively). The wash resistance offered by PermaNet was much better and longer lasting: Anopheles mortality after 4 washes was 92.6%, after 10 washes 83.7% and after 20 washes 87.1%. The limitations of commercially available wash-resistant nets are, however, their limited accessibility and the difficulty of replacing all existing bednets with a new product.

Insecticide treated mosquito nets for malaria control in India-experience from a tribal area on operational feasibility and uptake

“…Re-treatment -Besides distribution coverage, retreatment of nets every 6 or 12 months is one of the major constraints in large-scale implementation of ITNs (Gonzalez et al 2002). In the present study, bioassay results confirmed the efficacy of Cyfluthrin treatment of nets up to ten months on nets that were reportedly washed twice.…”

The efficacy of permethrin-treated military uniforms as a personal protection against Culex pipiens (Diptera: Culicidae) and its environmental consequences

“…New formulations of pyrethroid and other chemicals have been recently prepared that increases the lasting of insecticide on the fibers. For example, in Olyset Net, a strong bond is made between permethrin molecule and polyethylene fibers by a polymer that isn't broken even by frequent washing and sun light and heat (Gonzalez, et al, 2002). Also in Prema Net, deltamethrin insecticidal has been mixed by resin and made a bond around polyester fibers (WHO, 2000).…”

Fresh, dried or smoked? repellent properties of volatiles emitted from ethnomedicinal plant leaves against malaria and yellow fever vectors in Ethiopia

“…Even so, ITNs have their limitations; primarily, that they do not protect against exophagic vectors, or those vectors that bite at times when people are not sleeping under their bed nets. [4]. …”