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Effects of pyrethroid resistance on the cost effectiveness of a mass distribution of long-lasting insecticidal nets: a modelling study

Olivier JT Briët12*, Melissa A Penny12, Diggory Hardy12, Taiwo S Awolola3, Wim Van Bortel4, Vincent Corbel56, Roch K Dabiré7, Josiane Etang89, Benjamin G Koudou101112, Patrick K Tungu13 and Nakul Chitnis12

Author Affiliations

1 Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland

2 University of Basel, Basel, Switzerland

3 Molecular Entomology and Vector Control Research Laboratory, Nigerian Institute of Medical Research, PMB 2013, Yaba Lagos, Nigeria

4 Department Parasitology - Entomology, Institute of Tropical Medicine, Nationalestraat 155, B-2000, Antwerpen, Belgium

5 Institut de Recherche pour le Développement (IRD), Maladies Infectieuses et Vecteurs, Ecologie, Génétique, Evolution et Contrôle (IRD 224-CNRS 5290 UM1-UM2), Montpellier Cedex 5, France

6 Department of Entomology, Faculty of Agriculture, Kasetsart University, 10900, Bangkok, Thailand

7 Institut de Recherche en Sciences de la Santé (IRSS)/Centre Muraz (CM), 01 BP 390, Bobo-Dioulasso, Burkina Faso

8 Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale (OCEAC), BP. 288, Yaoundé, Cameroon

9 Faculty of Medicine and Pharmaceutical Sciences, University of Douala, P.O. Box 2701, Douala, Cameroon

10 Département Environnement et Santé, Centre Suisse de Recherches Scientifiques, 01 01 BP 1303, Abidjan, Côte d’Ivoire

11 UFR Sciences de la Nature, Université d’Abobo-Adjamé, 02 02 BP 801, Abidjan, Côte d’Ivoire

12 Centre for Neglected Tropical Diseases, Liverpool School of Tropical Medicine, L3 5QA, Liverpool, UK

13 Amani Medical Research Centre, National Institute for Medical Research, P.O. Box 81, Muheza, Tanzania

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Malaria Journal 2013, 12:77  doi:10.1186/1475-2875-12-77

Published: 25 February 2013

Abstract

Background

The effectiveness of insecticide-treated nets in preventing malaria is threatened by developing resistance against pyrethroids. Little is known about how strongly this affects the effectiveness of vector control programmes.

Methods

Data from experimental hut studies on the effects of long-lasting, insecticidal nets (LLINs) on nine anopheline mosquito populations, with varying levels of mortality in World Health Organization susceptibility tests, were used to parameterize malaria models. Both simple static models predicting population-level insecticidal effectiveness and protection against blood feeding, and complex dynamic epidemiological models, where LLINs decayed over time, were used. The epidemiological models, implemented in OpenMalaria, were employed to study the impact of a single mass distribution of LLINs on malaria, both in terms of episodes prevented during the effective lifetime of the batch of LLINs, and in terms of net health benefits (NHB) expressed in disability-adjusted life years (DALYs) averted during that period, depending on net type (standard pyrethroid-only LLIN or pyrethroid-piperonyl butoxide combination LLIN), resistance status, coverage and pre-intervention transmission level.

Results

There were strong positive correlations between insecticide susceptibility status and predicted population level insecticidal effectiveness of and protection against blood feeding by LLIN intervention programmes. With the most resistant mosquito population, the LLIN mass distribution averted up to about 40% fewer episodes and DALYs during the effective lifetime of the batch than with fully susceptible populations. However, cost effectiveness of LLINs was more sensitive to the pre-intervention transmission level and coverage than to susceptibility status. For four out of the six Anopheles gambiae sensu lato populations where direct comparisons between standard LLINs and combination LLINs were possible, combination nets were more cost effective, despite being more expensive. With one resistant population, both net types were equally effective, and with one of the two susceptible populations, standard LLINs were more cost effective.

Conclusion

Despite being less effective when compared to areas with susceptible mosquito populations, standard and combination LLINs are likely to (still) be cost effective against malaria even in areas with strong pyrethroid resistance. Combination nets are likely to be more cost effective than standard nets in areas with resistant mosquito populations.

Keywords:
Pyrethroid; Insecticide; Resistance; LLIN; ITN; Modelling; Piperonyl butoxide