Long-term field performance of a polyester-based long-lasting insecticidal mosquito net in rural Uganda

Albert Kilian,Francis Atieli,Olivier Pigeon,Chi Phan,Wilson Byamukama,Stephan Duchon

doi:10.1186/1475-2875-7-49

Abstract

BackgroundIn order to evaluate whether criteria for LLIN field performance (phase III) set by the WHO Pesticide Evaluation Scheme are met, first and second generations of one of these products, PermaNet®, a polyester net using the coating technology were tested.MethodsA randomized, double blinded study design was used comparing LLIN to conventionally treated nets and following LLIN for three years under regular household use in rural conditions. Primary outcome measures were deltamethrin residue and bioassay performance (60 minute knock-down and 24 hour mortality after a three minute exposure) using a strain of Anopheles gambiae s.s. sensitive to pyrethroid insecticides.ResultsBaseline concentration of deltamethrin was within targets for all net types but was rapidly lost in conventionally treated nets and first generation PermaNet® with median of 0.7 and 2.5 mg/m2 after six months respectively. In contrast, second generation PermaNet® retained insecticide well and had 41.5% of baseline dose after 36 months (28.7 mg/m2). Similarly, vector mortality and knockdown dropped to 18% and 70% respectively for first generation LLIN after six months but remained high (88.5% and 97.8% respectively) for second generation PermaNet® after 36 months of follow up at which time 90.0% of nets had either a knockdown rate ≥ 95% or mortality rate ≥ 80%.ConclusionSecond generation PermaNet® showed excellent results after three years of field use and fulfilled the WHOPES criteria for LLIN. Loss of insecticide on LLIN using coating technology under field conditions was far more influenced by factors associated with handling rather than washing.

Highlights

In order to evaluate whether criteria for long-lasting insecticidal net (LLIN) field performance set by the WHO Pesticide Evaluation Scheme are met, first and second generations of one of these products, PermaNet®, a polyester net using the coating technology were tested
This study reports on the long-term field performance of the initial as well as the improved, second generation product of PermaNet® as part of the phase III WHO Pesticide Evaluation Scheme (WHOPES) evaluation process
The drop in functional mortality over time (Table 3a) was more rapid and more pronounced than the 60 minute knockdown rates but both variables showed a pattern very similar to what was described for the chemical analysis: first generation LLINs showed a sharp decline after only 6 months with both functional mortality (18.1%) and knockdown rate (69.9%) significantly below the values of 80% and 95% respectively requested by WHOPES but maintained that level until 39 months of follow up

Summary

Introduction

In order to evaluate whether criteria for LLIN field performance (phase III) set by the WHO Pesticide Evaluation Scheme are met, first and second generations of one of these products, PermaNet®, a polyester net using the coating technology were tested. Up to date retreatment rates range from 2% to 20% in most instances and rarely reach more than 40% unless re-treatment is done by the public health services without cost to the consumer [2,3]. The solution to this problem and a true breakthrough in the ITN application is the concept of a long-lasting insecticidal net (LLIN), i.e. a net on which the insecticide effect lasts at least as long as the average useful live of that net even when it is used and washed regularly [4]. Attempts of increasing wash resistance of permethrin by adding polystyrene to the emulsifiable concentrate [5] showed a significantly prolonged effect but it was not long enough to last for the life of a net

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Conclusion