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Increased Susceptibility to Plasmodium Falciparum of Insecticide Resistant Anopheles in West Africa

How widespread is the increased susceptibility of insecticide-resistant Anopheles mosquitoes to Plasmodium infection and what are the risks associated with this phenomenon in relationship to the use of bed nets and insecticides? What policies should be adopted to reduce the risk of a major crisis in malaria control?

Project Summary

In the context of rapidly spreading pyrethroid resistance in Anopheles mosquitoes and emerging evidence that this insecticide-resistance may increase mosquito susceptibility to Plasmodium infection, malaria control faces challenges never seen before. This project aims to assess how widespread the increased susceptibility of insecticide-resistant Anopheles to Plasmodium infection is, and the risk associated with this phenomenon in relationship to human behaviour regarding the use of bed nets and insecticides in three localities: Dielmo in Senegal, Tiassalé in Côte d’Ivoire, and Tori-Bossito in Benin. Anopheline mosquitoes from these localities will be experimentally exposed to infected blood and genotyped to measure how the probability of infection is related to the genotype at the locus responsible for insecticide resistance in these three mosquito populations.

A number of other entomological parameters will be measured to assess malaria transmission in each locality, and additional sociological and anthropological data on human behaviour related to prevention of mosquito bites will be collected. These data will be used to assess the risk of setbacks in malaria control (i.e. the risk of halting of the steady decrease in malaria incidence that has been observed in the past few years, or even increasing malaria incidence) and secondly, the risk of malaria transmission being higher with infection-susceptible insecticide resistant mosquitoes than it used to be before the scale-up of insecticide treated nets, when mosquitoes were insecticide susceptible and less susceptible to infection. If the second risk is substantial, this could translate into a crisis for malaria control. This research is expected to influence policy on recommendations about the use of bed nets and insecticides, and will help to plan the future of malaria control.

Academic Output

Working Paper

Increased Susceptibility to Plasmodium Falciparum of Insecticide Resistant Anopheles in West Africa

The scale-up of control strategies targeting malaria vectors (Anopheles mosquitoes) such as indoor residual spraying (IRS), insecticide-treated bed nets (ITNs) and the destruction of breeding sites has led to huge progress in the control of malaria in Sub-Saharan African countries. However, in recent years, the widespread use of insecticides in agriculture and bed net treatment contributed to the evolution of resistant mosquito strains. Resistance to pyrethroids is a particular threat for malaria control, since pyrethroids are currently the only recommended and approved insecticides for treating bed nets, primarily because of their low toxicity to humans compared to other pesticides. Therefore, there is great concern that rapidly spreading pyrethroid resistance may annul recent successes in the fight against malaria with ITNs. This project aimed to assess how rates of malaria transmission depend on the alleles associated with pyrethroid resistance, and concomitant behavioural changes in mosquitoes and humans.

Executive Summary

Rapidly spreading pyrethroid resistance in Anopheles mosquitoes and emerging evidence that this may increase mosquito susceptibility to Plasmodium infection, present novel challenges for malaria control. This project aimed to assess how widespread is increased susceptibility of insecticide-resistant Anopheles to Plasmodium. It assessed the associated risks in relation to the use of bed nets and insecticides by populations in Dielmo in Senegal, Agboville in Côte d’Ivoire, and Tori-Bossito in Benin. Our results confirm that resistant mosquitoes  (bearing the kdr  L1014F allele) tend to have higher infection rates than sensitive mosquitoes, both in wild populations and via experimental infection. However, decreases in mosquito densities due to the intensive application of vector control compensate for this phenomenon. The sociological data indicate that awareness of resistance in mosquitoes may lead to reduced vigilance and less use of bed-nets, which is of special concern in this context. We provide a set of policy recommendations to address these issues.

Research Team

Thomas Smith
Coordinator
University of Basel

Nadja Cereghetti
Co-Coordinator
Swiss TPH / University of Basel

Emilia Azalou Tingbe
Principal Member
CEPAD, Bénin

Olivier Briet
Principal Member
Swiss TPH / University of Basel

Aurélie Cailleau
Principal Member
CSRS Côte d’Ivoire / Institut Pasteur Dakar (IPD)

Nakul Chitnis
Principal Member
Swiss TPH / University of Basel

Mouhamadou Chouaïbou Seïdou
Principal Member
Centre Suisse de Recherches Scientifiques CSRS

Sylvain L. Faye
Principal Member
Université Cheik Anta Diop (UCAD), Dakar

Gilbert Fokou
Principal Member
Centre Suisse de Recherches Scientifiques (CSRS)

Yadouleton William Anges
Principal Member
Centre de Recherche Entomologique de Cotonou (CREC), Bénin

Rock Aikpon
Associated Member
Centre de Recherche Entomologique de Cotonou (CREC), Bénin

Souleymane Doucoure
Associated Member
IRD Dakar

Dia Ibrahima
Associated Member
Institut Pasteur Dakar (IPD)

Vincent Richard
Associated Member
Institut Pasteur Dakar (IPD)

Jean-François Trape
Associated Member
Institut pour la Recherche et le Développement (IRD)

Status

completed

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