Abstract
BackgroundLong-lasting treatment kits, designed to transform untreated nets into long-lasting insecticidal nets (LLINs), may facilitate high coverage with LLINs where non-treated nets are in place. In this study, the efficacy of ICON® Maxx (Syngenta) was evaluated under laboratory conditions and in an experimental hut trial in central Côte d'Ivoire, where Anopheles gambiae s.s. are resistant to pyrethroid insecticides.MethodsIn the laboratory, polyester and polyethylene net samples were treated with ICON® Maxx, washed up to 20 times and their efficacy determined in World Health Organization (WHO) cone assays against a susceptible laboratory An. gambiae s.s. colony. Over a 12-month period, the polyester nets were evaluated in a hut trial to determine mosquito deterrence, induced exophily, blood-feeding inhibition and mortality.ResultsIn the laboratory, ICON® Maxx-treated polyethylene nets showed higher efficacy against pyrethroid-susceptible mosquitoes than polyester nets. After 20 washings, insecticidal efficacy in bioassays was 59.4% knockdown (KD) and 22.3% mortality for polyethylene, and 55.3% KD and 17.9% mortality for polyester nets. In experimental huts, treated nets showed strong deterrence, induced exophily and an over three-fold reduction in blood-fed mosquitoes. More than half (61.8%) of the mosquitoes entering the huts with treated nets were found dead the next morning despite high levels of KD resistance. After washing the treated nets, KD and mortality rates were close to or exceeded predefined WHO thresholds in cone bioassays.ConclusionIn contrast to previous laboratory investigation, ICON® Maxx-treated nets showed only moderate KD and mortality rates. However, under semi-field conditions, in an area where mosquitoes are resistant to pyrethroids, ICON® Maxx showed high deterrence, induced exophily and provided a significant reduction in blood-feeding rates; features that are likely to have a positive impact in reducing malaria transmission. The WHO cone test may not always be a good proxy for predicting product performance under field conditions.
Highlights
Long-lasting treatment kits, designed to transform untreated nets into long-lasting insecticidal nets (LLINs), may facilitate high coverage with LLINs where non-treated nets are in place
After 20 washings, KD rates were considerably below the mean KD defined for LLINs by World Health Organization Pesticide Evaluation Scheme (WHOPES) guideline (i.e. 95% after 20 washings)
An. gambiae s.s. induced exophily recorded in the treated huts was significantly higher than the one recorded in the control huts (RR = 4.31, 95% confidence intervals (CI): 3.56-5.22) (Table 3)
Summary
Long-lasting treatment kits, designed to transform untreated nets into long-lasting insecticidal nets (LLINs), may facilitate high coverage with LLINs where non-treated nets are in place. Under semi-field conditions, in an area where mosquitoes are resistant to pyrethroids, ICON® Maxx showed high deterrence, induced exophily and provided a significant reduction in blood-feeding rates; features that are likely to have a positive impact in reducing malaria transmission. As conventional ITNs need to be re-treated with insecticide at least once a year, or after two or three washes, their effective protection in the long-term may be compromised [4]. To overcome this constraint, manufacturers have developed long-lasting insecticidal nets (LLINs). There is a growing demand for LLINs within the frame of national malaria control programmes, so that the target of at least 85% of the at-risk populations to sleep under an ITN by 2015 can be reached [14,15]
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