Entomological evaluation of three brands of manufactured insecticidal nets and of nets conventionally treated with deltamethrin, after repeated washing

Abstract

The present study evaluated the efficacy and wash resistance of three types of commercial, deltamethrin-treated nets (PermaNet, Yorkool and A-Z nets) - that their manufacturers claimed to be long-lasting insecticidal nets (LLIN) - and those of nets conventionally treated with deltamethrin, at either 23-27 mg/m(2) (using one K-O Tab tablet/net) or 46-54 mg/m(2) (using two K-O Tab tablets/net). The nets were tested unwashed or after being washed, by hand or machine, five or 15 times. After each wash, the nets were dried vertically on a line, in the shade, for 8 h. Insecticidal activity was assessed, using two types of bio-assay and wild-caught female Anopheles stephensi, as mean median knock-down times and as mortality 24 h after a 3-min exposure. For each type of nets tested, the insecticidal activity of the unwashed nets was greater than that of the nets washed five washes, and that of the nets washed five times was greater than that of the nets washed 15 times, with the latter decline considerably greater than the former. The pattern of decrease, however, differed with net type. The PermaNet and A-Z nets generally had the highest insecticidal activity, and, overall, the Yorkool nets did not perform significantly better than the conventional nets treated with 23-27 mg deltamethrin/m(2). Although washing with detergents can clearly remove insecticide from the fibres of all types of treated nets, the consequent loss of activity varies with net type. After 15 washes, the PermaNet nets showed higher insecticidal activity than any other net type but there is still scope for the manufacturer of the PermaNet nets to improve wash resistance.

Entomological evaluation of PermaNet 2.0®and K-O Tab 1-2-3®treated nets in comparison to nets conventionally treated with deltamethrin, after repeated washing

“…In previous studies, the wash resistance of PermaNet2 was found to be similar to the results of wash resistance of PN2 (new generation of PermaNet2) up to 15 washes. 2,17,18,20,21 In the present study, the results showed better wash resistance of PN2 in comparison to PermaNet2 up to 21 washes. 21 22,23,26 In two studies that were carried out by Yates et al and Oxborough et al on wash resistance of KO 123, although their studies were laboratory based and they used WHO laboratory washing methods, they reported similar results to our study and confirmed that KO 123 is LLITNs.…”

“…Previous studies published by the first author of this study reported almost identical results (40% and 64.8% mortality in comparison to 62% mortality in the present study). 3,17 Other researchers have reported different results.…”

“…There is inconsistency for this result between different laboratories and field studies around the world. 17 This could be because of different hand washing methods, varieties of detergents or soaps and chemical or physical factors of water used for washing. Previous studies published by the first author of this study reported almost identical results (40% and 64.8% mortality in comparison to 62% mortality in the present study).…”

Laboratory and field evaluation of the impact of washings on the effectiveness of LifeNet®, Olyset® and PermaNet® 2.0 in two areas, where there is a high level of resistance of Anopheles gambiae to pyrethroids, Benin, West Africa

“…[3], Hodjati and Curtis [10] and Chandre et al [11]. It is obvious that repeated washing of LLINs can result in a reduction in efficacy due to loss of insecticide [12,13]. The excito-repellent effect of the deltamethrin (LifeNet®, Permanet®) and of permethrin (Olyset®), which explains the increase of the exophily, appeared differently in the three LLINs., by considering data from the experimental huts and the tunnel tests, it can be concluded that repeated washings does not completely affect the repellent effect.…”

“…Among the three LLINs evaluated, Olyset® and Permanet® 2.0 have been on the market the longest and are the most studied. Most of the studies carried out comparing the bio-efficacy of the two market-dominant LLINs [12] have consistently shown that Olyset® is more wash durable and less bio-effective compared to Permanet®. This may be because of the treatment technology used and netting material (Duchon S: Regeneration, wash resistance and efficacy of long-lasting insecticidal mosquito nets (LifeNet) from Bayer CropScience against susceptible mosquitoes of Anopheles gambiae , umpublished report).…”