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Ahead of Print -Increased Pyrethroid Resistance in Malaria Vectors and Decreased Bed Net Effectiveness, Burkina Faso - Volume 20, Number 10—October 2014 - Emerging Infectious Disease journal - CDC

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Ahead of Print -Increased Pyrethroid Resistance in Malaria Vectors and Decreased Bed Net Effectiveness, Burkina Faso - Volume 20, Number 10—October 2014 - Emerging Infectious Disease journal - CDC

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Volume 20, Number 10—October 2014


Increased Pyrethroid Resistance in Malaria Vectors and Decreased Bed Net Effectiveness, Burkina Faso

Kobié H. Toé, Christopher M. Jones, Sagnon N’Fale, Hanafy M. Ismail, Roch K. Dabiré, and Hilary RansonComments to Author 
Author affiliations: Liverpool School of Tropical Medicine, Liverpool, UK (K.H. Toé, C.M. Jones, H.M. Ismail, H. Ranson)Centre National de Recherche et de la Formation sur Paludisme, Ouagadougou, Burkina Faso (K.H. Toé, S. N’Fale)Institut de Recherche en Sciences de la Santé/Centre Muraz, Bobo-Dioulasso, Burkina Faso (R.K. Dabiré)


Malaria control is dependent on insecticides. Increases in prevalence of insecticide resistance in malaria vectors across Africa are well-documented. However, few attempts have been made to quantify the strength of this resistance and link it to the effectiveness of control tools. Using quantitative bioassays, we show that in Burkina Faso pyrethroid resistance in Anopheles gambiae mosquitoes has increased in intensity in recent years and now exceeds 1,000-fold. In laboratory assays, this level of resistance renders insecticides used to impregnate bed nets ineffective. Thus, the level of personal and community protection afforded by long-lasting insecticide-treated net campaigns will probably be reduced. Standardized methods are needed to quantify resistance levels in malaria vectors and link these levels to failure of vector control methods.
Long-lasting insecticide–treated bed nets (LLINs) have been shown repeatedly to provide protection against malaria transmission in Africa and reduce childhood mortality rates by ≈20% (1). Distribution of LLINs has increased over the past decade, and an estimated 54% of households at risk for malaria in sub-Saharan Africa have ≥1 LLIN. This factor has been a major contributor in reducing malaria incidence; the estimated malaria mortality rate for Africa has decreased by ≈49% since 2000 (2). These advances are now threatened by rapid selection and spread of resistance to insecticides in malaria vectors (3). Resistance to pyrethroids, the only class of insecticides available for use on LLINs, is now widespread in Anopheles gambiae and An. funestus mosquitoes, the major malaria vectors (4).
To standardize monitoring for insecticide resistance, the World Health Organization (WHO) has developed simple bioassays that use filter papers impregnated with insecticide at a predefined diagnostic dose. A population is described as resistant to an insecticide if a mortality rate >90% is observed in these tests (5). These assays are useful for detecting resistance when it first appears in the population. However, these assays do not provide any information on the strength of this resistance. This information is crucial for assessing the likely effect of this resistance on effectiveness of vector control tools. The Global Plan for Insecticide Resistance Management in Malaria Vectors (3) recommends that all malaria-endemic countries monitor insecticide resistance in local vectors. However, because the correlation between results of diagnostic dose assays and control effectiveness remains undefined, simple detection of resistance in a mosquito population is not sufficient evidence to implement a change in insecticide policy.
In this study, we used variants of WHO assays and bottle assays of the Centers for Disease Control and Prevention (CDC) (Atlanta, GA, USA) to quantify the level of pyrethroid resistance in a population of An. gambiae mosquitoes from Burkina Faso over a 3-year period. A high level of resistance was observed. The lack of comparator data from across Africa makes it impossible to conclude whether the pyrethroid resistance levels seen in Burkina Faso are atypical. However, these data should raise concerns for malaria control across Africa because we demonstrate that this level of resistance is causing operational failure of the insecticides used in LLINs.

Mr Toé is a doctoral student at the Liverpool School of Tropical Medicine, Liverpool, UK. His research interests are evaluating the distribution, causes, and effects of insecticide resistance in malaria vectors in Africa.


K.H.T., C.M.J., and H.M.I performed the experiments and analyzed the data; C.M.J. and H.R. designed the study; K.H.T., C.M.J., and H.R wrote the manuscript; and S.N. and R.K.D. supervised the field work.
This study was supported by European Union Seventh Framework Programme FP7 (2007–2013) under grant agreement no. 265660 AecNet.


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Suggested citation for this article: Toé KH, Jones CM, N’Fale S, Ismail HM, Dabiré RK, Ranson H. Increased pyrethroid resistance in malaria vectors and decreased bed net effectiveness in Burkina Faso. Emerg Infect Dis [Internet]. 2014 Oct [date cited]. http://dx.doi.org/10.3201/eid2010.140619
DOI: 10.3201/eid2010.140619

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