Design of a study to determine the impact of insecticide resistance on malaria vector control: a multi-country investigation

Abstract

BackgroundProgress in reducing the malaria disease burden through the substantial scale up of insecticide-based vector control in recent years could be reversed by the widespread emergence of insecticide resistance. The impact of insecticide resistance on the protective effectiveness of insecticide-treated nets (ITN) and indoor residual spraying (IRS) is not known. A multi-country study was undertaken in Sudan, Kenya, India, Cameroon and Benin to quantify the potential loss of epidemiological effectiveness of ITNs and IRS due to decreased susceptibility of malaria vectors to insecticides. The design of the study is described in this paper.MethodsMalaria disease incidence rates by active case detection in cohorts of children, and indicators of insecticide resistance in local vectors were monitored in each of approximately 300 separate locations (clusters) with high coverage of malaria vector control over multiple malaria seasons. Phenotypic and genotypic resistance was assessed annually. In two countries, Sudan and India, clusters were randomly assigned to receive universal coverage of ITNs only, or universal coverage of ITNs combined with high coverage of IRS. Association between malaria incidence and insecticide resistance, and protective effectiveness of vector control methods and insecticide resistance were estimated, respectively.ResultsCohorts have been set up in all five countries, and phenotypic resistance data have been collected in all clusters. In Sudan, Kenya, Cameroon and Benin data collection is due to be completed in 2015. In India data collection will be completed in 2016.DiscussionThe paper discusses challenges faced in the design and execution of the study, the analysis plan, the strengths and weaknesses, and the possible alternatives to the chosen study design.

Insecticide-treated nets provide protection against malaria to children in an area of insecticide resistance in Southern Benin

“…In this study, two important confounders (age and SES) were adjusted for which made little impact on the analysis, but some residual confounding may remain [9]. …”

Identification, Validation, and Application of Molecular Diagnostics for Insecticide Resistance in Malaria Vectors

“…While insecticide resistance is viewed as a threat to the efficacy of LLIN and IRS interventions, its effects on entomological outcomes and disease transmission have proven difficult to quantify [57, 58]. It cannot be assumed that a resistant mosquito will exacerbate malaria transmission, as the genetic variants which confer resistance may also alter mosquito survival and vectorial capacity.…”

Lessons learned, challenges and outlooks for decision-making after a decade of experience monitoring the impact of Indoor Residual Spraying in Benin, West Africa

“…In addition, a report of Gates and Melinda project implemented from 2011 to 2015 in Benin, Cameroon, Kenya, India and Sudan on the impact of vector resistance on the efficacy of vector control tools (LLINs and IRS) showed mitigated results. In this study, the authors found very little correlation between the decrease of entomological parameters and parasitological and clinical parameters [14][15][16][17]. Another study on the efficacy of four vector control interventions supported by the French Ministry of Cooperation in an area of high vector insecticide resistance in Benin did not show significant differences from one intervention to another [18,19].…”