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Efficacy of ICON® Maxx in the laboratory and against insecticide-resistant Anopheles gambiae in central Côte d'Ivoire.

Winkler MS, Tchicaya E, Koudou BG, Donzé J, Nsanzabana C, Müller P, Adja AM, Utzinger J - Malar. J. (2012)

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, CH-4002 Basel, Switzerland.

ABSTRACT

Background: 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. 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.

Methods: In 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.

Results: In 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.

Conclusion: In 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.

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Development of mean mortality rates (24 h post-exposure) after 3 min bioassay test for An. gambiae Kisumu-susceptible strain over a 12-month experimental hut trial in the M'Bé station, central Côte d'Ivoire, including the effect of the washings on treated an control nets (*data omitted due to insufficient number of mosquitoes).
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Figure 5: Development of mean mortality rates (24 h post-exposure) after 3 min bioassay test for An. gambiae Kisumu-susceptible strain over a 12-month experimental hut trial in the M'Bé station, central Côte d'Ivoire, including the effect of the washings on treated an control nets (*data omitted due to insufficient number of mosquitoes).

Mentions: The dynamics of the mean KD and mortality rates of the cone bioassay efficacy test are shown in Figures 4 and 5. Over the 12-month experimental hut trial period, mean KD of An. gambiae Kisumu exposed to the treated nets remained at relatively high levels with a trend of higher KDs in the second half of the trial following net washing. Mean KDs for untreated net samples that served as controls were very low, with a small peak in January 2009 (unwashed control: 8.0%; washed control: 18.0%).


Efficacy of ICON® Maxx in the laboratory and against insecticide-resistant Anopheles gambiae in central Côte d'Ivoire.

Winkler MS, Tchicaya E, Koudou BG, Donzé J, Nsanzabana C, Müller P, Adja AM, Utzinger J - Malar. J. (2012)

Development of mean mortality rates (24 h post-exposure) after 3 min bioassay test for An. gambiae Kisumu-susceptible strain over a 12-month experimental hut trial in the M'Bé station, central Côte d'Ivoire, including the effect of the washings on treated an control nets (*data omitted due to insufficient number of mosquitoes).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3369213&req=5

Figure 5: Development of mean mortality rates (24 h post-exposure) after 3 min bioassay test for An. gambiae Kisumu-susceptible strain over a 12-month experimental hut trial in the M'Bé station, central Côte d'Ivoire, including the effect of the washings on treated an control nets (*data omitted due to insufficient number of mosquitoes).
Mentions: The dynamics of the mean KD and mortality rates of the cone bioassay efficacy test are shown in Figures 4 and 5. Over the 12-month experimental hut trial period, mean KD of An. gambiae Kisumu exposed to the treated nets remained at relatively high levels with a trend of higher KDs in the second half of the trial following net washing. Mean KDs for untreated net samples that served as controls were very low, with a small peak in January 2009 (unwashed control: 8.0%; washed control: 18.0%).

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, CH-4002 Basel, Switzerland.

ABSTRACT

Background: 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. 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.

Methods: In 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.

Results: In 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.

Conclusion: In 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.

Show MeSH
Related in: MedlinePlus