Abstract
BackgroundLong-lasting insecticidal nets (LLINs) are advocated by WHO for protection against malaria. Of the three brands of LLINs currently approved by WHO, Olyset® is the only one currently granted full recommendation. With this type of LLIN, the insecticide (permethrin) is incorporated into the polyethylene fibre during manufacture and diffuses from the core to the surface, thereby maintaining surface concentrations. It has not been determined for how long Olyset nets remain protective against mosquitoes in household use.MethodsExamples of Olyset nets, which had been in use in Tanzanian villages for seven years, were tested in experimental huts against naturally entering Anopheles gambiae and Anopheles funestus mosquitoes. Performance was compared with new Olyset nets, conventionally treated ITNs (either newly treated with alphacypermethrin or taken from local villages after 1.5 years of use) and untreated nets. All nets were artificially holed except for the seven-year Olyset nets, which had developed holes during prolonged domestic use.ResultsAnopheles funestus and An. gambiae in NE Tanzania are susceptible to pyrethroids. The new Olyset nets caused high mortality against An. funestus (73.9%) and An. gambiae (62.7%) in experimental huts. The seven-year Olyset nets caused 58.9% mortality against An. funestus and 40.0% mortality against An. gambiae. The freshly treated alphacypermethrin nets also caused high mortality against An. funestus (70.6%) and An. gambiae (72.0%); this decreased to 58.4% and 69.6% respectively after 1.5 years of use. The new Olyset nets inhibited blood-feeding by 40–50%. The 7 year Olyset nets showed no feeding inhibition over that shown by the untreated nets. The alphacypermethrin treated nets failed to inhibit blood-feeding after 1.5 years of use. However iHhhdn laboratory tunnel tests samples of all types of treated net including the 7 year Olyset inhibited blood-feeding by more than 95%.ConclusionAfter seven years of use Olyset nets were still strongly insecticidal. Mosquito mortality decreased by only 20–35% over this period. However, Olyset would not provide personal protection after seven years unless it was in good condition and all holes fully repaired.
Highlights
Long-lasting insecticidal nets (LLINs) are advocated by WHO for protection against malaria
Long-lasting insecticidal nets (LLINs) in which the insecticide treatment is intended to last for the lifetime of the net are advocated by the World Health Organization for protection against malaria [1]
Of the 3 brands of LLIN currently approved by the WHO Pesticide Evaluation Scheme, Olyset® (Sumitomo Chemical Co., Ltd, Japan) is the longest established and is the only LLIN to be granted full, as opposed to interim, recommendation [3,4]
Summary
Long-lasting insecticidal nets (LLINs) are advocated by WHO for protection against malaria. With this type of LLIN, the insecticide (permethrin) is incorporated into the polyethylene fibre during manufacture and diffuses from the core to the surface, thereby maintaining surface concentrations It has not been determined for how long Olyset nets remain protective against mosquitoes in household use. Of the 3 brands of LLIN currently approved by the WHO Pesticide Evaluation Scheme, Olyset® (Sumitomo Chemical Co., Ltd, Japan) is the longest established and is the only LLIN to be granted full, as opposed to interim, recommendation [3,4] With this brand of LLIN, the pyrethroid insecticide (permethrin) is incorporated into the polyethylene fibre during manufacture and diffuses gradually from the core to the surface. Olyset has been in use in some Tanzanian villages for several years and according to cone bioassay tests retains insecticidal activity for at least seven years [7]
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