Do holes in long-lasting insecticidal nets compromise their efficacy against pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus? Results from a release–recapture study in experimental huts
Open Access
- 28 August 2015
- journal article
- research article
- Published by Springer Science and Business Media LLC in Malaria Journal
- Vol. 14 (1), 1-22
- https://doi.org/10.1186/s12936-015-0836-7
Abstract
Resistance of malaria vectors to pyrethroids threatens the effectiveness of long-lasting insecticidal nets (LLINs) as a tool for malaria control. Recent experimental hut and observational studies in Benin show that pyrethroid resistance reduces the insecticidal effect and personal protection of LLINs especially when they become torn. The World Health Organization has proposed a threshold for when nets are “too torn” at 1,000 cm2 for rectangular holes and 790 cm2 for round holes. This study examines whether there is a threshold above which LLINs no longer reduce malaria transmission. Intact and artificially-holed LLINs under three months old and untreated nets were tested by releasing mosquitoes from a susceptible Anopheles gambiae colony, a pyrethroid-resistant An. gambiae population and a resistant Culex quinquefasciatus population in closed experimental huts in Southern Benin, West Africa. The efficacy of LLINs and untreated nets was evaluated in terms of protection against blood feeding, insecticidal effect and potential effect on malaria transmission. Personal protection by both LLINs and untreated nets decreased exponentially with increasing holed surface area, without evidence for a specific threshold beyond which LLINs could be considered as ineffective. The insecticidal effect of LLINs was lower in resistant mosquitoes than in susceptible mosquitoes, but holed surface area had little or no impact on the insecticidal effect of LLINs. LLINs with 22,500 cm2 holed surface area and target insecticide content provided a personal protection of 0.60 (95 % CI 0.44–0.73) and a low insecticidal effect of 0.20 (95 % CI 0.12–0.30) against resistant An. gambiae. Nevertheless, mathematical models suggested that if 80 % of the population uses such nets, they could still prevent 94 % (95 % CI 89–97 %) of transmission by pyrethroid-resistant An. gambiae. Even though personal protection by LLINs against feeding mosquitoes is strongly reduced by holes, the insecticidal effect of LLINs is independent of the holed surface area, but strongly dependent on insecticide resistance. Badly torn nets that still contain insecticide have potential to reduce malaria transmission. The relationship between LLIN integrity and efficacy needs to be understood in order to guide LLIN distribution policy.Keywords
Funding Information
- International Master of Entomology (MIE), Cotonou, Benin
- West African Anopheles Biology and Control network (ABC)
- Institut de Recherche pour le Developpement (IRD-MIVEGEC)
- Institut Pasteur de Madagascar (IPM)
This publication has 49 references indexed in Scilit:
- User-determined end of net life in Senegal: a qualitative assessment of decision-making related to the retirement of expired netsMalaria Journal, 2013
- Clustering of host-seeking activity of Anopheles gambiae mosquitoes at the top surface of a human-baited bed netMalaria Journal, 2013
- Effects of pyrethroid resistance on the cost effectiveness of a mass distribution of long-lasting insecticidal nets: a modelling studyMalaria Journal, 2013
- Physical condition and maintenance of mosquito bed nets in Kwale County, coastal KenyaMalaria Journal, 2013
- Combining indoor residual spraying with chlorfenapyr and long-lasting insecticidal bed nets for improved control of pyrethroid-resistant Anopheles gambiae: an experimental hut trial in BeninMalaria Journal, 2011
- Evidence for a useful life of more than three years for a polyester-based long-lasting insecticidal mosquito net in Western UgandaMalaria Journal, 2011
- Efficacy of long-lasting insecticidal nets in use in Macha, Zambia, against the local Anopheles arabiensis populationMalaria Journal, 2011
- Efficacy of PermaNet® 2.0 and PermaNet® 3.0 against insecticide-resistant Anopheles gambiae in experimental huts in Côte d'IvoireMalaria Journal, 2011
- Field efficacy of a new mosaic long-lasting mosquito net (PermaNet® 3.0) against pyrethroid-resistant malaria vectors: a multi centre study in Western and Central AfricaMalaria Journal, 2010
- Expression of the cytochrome P450s, CYP6P3 and CYP6M2 are significantly elevated in multiple pyrethroid resistant populations of Anopheles gambiae s.s. from Southern Benin and NigeriaBMC Genomics, 2008