title: 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.
abstract: BACKGROUND
  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 cm(2) for rectangular holes and 790 cm(2) for round holes. This study examines whether there is a threshold above which LLINs no longer reduce malaria transmission.
  
  
  METHODS
  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.
  
  
  RESULTS
  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 cm(2) 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.
  
  
  CONCLUSIONS
  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.
authors: Institut Pasteur de Madagascar, Antananarivo, Madagascar. sanji@pasteur.mg.
authors: Sanjiarizaha
authors: S
authors: Randriamaherijaona
authors: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland. olivier.briet@unibas.ch.|University of Basel, Basel, Switzerland. olivier.briet@unibas.ch.
authors: Olivier J T
authors: OJ
authors: Briët
authors: Institut Pasteur de Madagascar, Antananarivo, Madagascar. seboyer@pasteur.mg.
authors: Sébastien
authors: S
authors: Boyer
authors: Centre de Recherches Entomologiques de Cotonou (CREC), 06 BP 2604, Cotonou, Republic of Benin. azlesage@yahoo.fr.
authors: Aziz
authors: A
authors: Bouraima
authors: Centre de Recherches Entomologiques de Cotonou (CREC), 06 BP 2604, Cotonou, Republic of Benin. raphael.n'guessan@lshtm.ac.uk.|Department of Disease Control, London School of Hygiene and Tropical Medicine, Keppel street, London, WC1E 7HT, UK. raphael.n'guessan@lshtm.ac.uk.
authors: Raphael
authors: R
authors: N'Guessan
authors: Institut Pasteur de Madagascar, Antananarivo, Madagascar. crogier@pasteur.mg.|Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes, UM 63, CNRS 7278, IRD 198, INSERM 1095, Aix Marseille Université, Marseille, France. crogier@pasteur.mg.|Institut de Recherche Biomédicale des Armées, Brétigny sur Orge, France. crogier@pasteur.mg.
authors: Christophe
authors: C
authors: Rogier
authors: Institut de Recherche pour le Développement, Maladies Infectieuses et Vecteurs, Ecologie, Génétique, Evolution et Contrôle (IRD 224-CNRS 5290 UM1-UM2), Montpellier, France. vincent.corbel@ird.fr.|Department of Entomology, Faculty of Agriculture at Kamphaeng Saen, Kamphaeng Saen Campus, Kasetsart University, Nakhon Pathom, 73140, Thailand. vincent.corbel@ird.fr.
authors: Vincent
authors: V
authors: Corbel
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects*; D001522:Behavior, Animal; D001541:Benin; D001681:Biological Assay; D003465:Culex / Q000187:drug effects*; D005260:Female; D006801:Humans; D007303:Insect Vectors / Q000187:drug effects*; D007305:Insecticide Resistance; D057148:Insecticide-Treated Bednets / Q000706:statistics & numerical data*; D008288:Malaria / Q000517:prevention & control; D008297:Male; D009032:Mosquito Control / Q000379:methods; D011722:Pyrethrins / Q000494:pharmacology*
chemical_list: D011722:Pyrethrins