Evaluation Of Wash Resistance Of Longlastng Insecticidal Nets Currently Available In Ethiopia And Comparison With Conventionally Treated Nets

ITNs are widely promoted as means of preventing man- vector contact in the control of malaria.rnDevelopment of Long Lasting Insecticidal Nets (LLINs) avoids the need for re-treatment which was arnmajor operational problem faced by net owners. There are, however several factors which affect thernefficacy of ITNs. Washing is one among the factors affecting the efficacy of ITNs by reducing thernlethal concentration of insecticides on the net surface.rnThe objective of this study was to evaluate wash resistance of LLIN, currently available in Ethiopia, inrntwo different washing procedures and compare with conventionally treated nets (CTNs) subject tornrepeated washes. Two types of LLINs: (1) Olyset (2) PermaNet and net treated conventionallyrnwith deltamethrin were exposed to two different washing procedures (washed on stone and basin).rnThen all nets were subject to mosquito bio- assay on WHO cone test. Mosquitoes were exposed to eachrnnet for three minutes. Knockdown rate was measured 60 minutes after exposure and mortality rate wasrnmeasured 24 hr after exposure. Effect of sunlight on the efficacy of nets was also assessed.rnLLINs performed well than CTNs in both washing procedures. PermaNet, relatively, was the mostrnwash resistant with 80% mosquito mortality in WHO cone bioassays after as many as 20 washes in netsrnwashed on basin and 65% in nets washed on stone. Olyset was also as wash resistant as PermaNetrnwith >75% mortality after 20 washes in nets washed on basin but when washed on stone, Olysetrnperformed less than PermaNet with mosquito mortality 50% after 20 washes, P= 0.032. CTNs werernthe least wash resistant in both cases with 60% mosquito mortality in nets washed on basin and 33.3%rnin nets washed on stone just after 5 washes. Wash resistance of a net had significant difference whenrnwashed on stone and basin, P=0.031 by ANOVA. Nets dried in direct sunlight or in shade had nornsignificant difference in mosquito mortality or knockdown rate, P= 0.602. In general, washing ITNsrnharshly rubbing on stone reduces effective life span of insecticides on nets so rapidly as compared tornnets washed on basin. So washing nets gently should be recommended to keep LLINs effectivernthroughout their physical life span.rnKey words: LLINs, CTNs, washing procedures, wash resistance, efficacy

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