Benchmarking insecticide resistance intensity bioassays for Anopheles malaria vector species against resistance phenotypes of known epidemiological significance

Abstract

BackgroundInsecticide use via indoor residual spraying (IRS) or treated nets is the primary method for controlling malaria vector populations. The incidence of insecticide resistance in vector populations is burgeoning globally making resistance management key to the design of effective malaria control and elimination strategies. Vector populations can be assessed for insecticide resistance using a binary (susceptible or resistant) classification based on the use of the standard WHO insecticide susceptibility assay for adult anopheline mosquitoes. However, the recent scaling up of vector control activities has necessitated a revision of the WHO bioassay protocol to include the production of information that not only diagnoses resistance but also gives information on the intensity of expression of resistance phenotypes detected. This revised protocol is expected to inform on the range of resistance phenotypes in a target vector population using discriminating/diagnostic insecticide concentrations (DC) as well as their potential operational significance using 5× DC and 10× DC assays. The aim of this project was to use the revised protocol to assess the intensity of pyrethroid resistance in a range of insecticide resistant Anopheles strains with known resistance mechanisms and for which there is evidence of operational significance in the field setting from which these colonies were derived.MethodsDiagnostic concentration (DC) bioassays followed by 5× DC and 10× DC assays using the pyrethroid insecticides permethrin and deltamethrin were conducted according to the standard WHO bioassay method against pyrethroid resistant laboratory strains of Anopheles funestus, An. arabiensis and An. gambiae.ResultsLow to moderate resistance intensities were recorded for the An. arabiensis and An. gambiae strains while moderate to high intensities were recorded for the An. funestus strains.ConclusionsIt is evident that resistance intensity assays can add predictive value to the decision making process in vector control settings, although more so in an IRS setting and especially when bench-marked against resistance phenotypes of known operational significance.

Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide‐treated bed nets

“…funestus strains from southern Mozambique that have been maintained at the VCRL since 2000. Selection of the FUMOZ‐BASE strain with 0.1% lambda‐cyhalothrin, a pyrethroid, from 2000 to 2005 generated the FUMOZ‐R strain, which has increased resistance to pyrethroids and carbamates (Hunt et al., ), which is still present in FUMOZ‐BASE (Venter et al., ). No kdr alleles are present in either strain (Okoye, Brooke, Hunt, & Coetzee, ), so the resistance is due to metabolic changes (Amenya et al., ; Wondji et al., ).…”

“…strain colonized in 2010 from mosquitoes collected in Tongon, Côte d'Ivoire. The colony is resistant to pyrethroids, DDT, carbamates, and organophosphates, but the resistance mechanisms remain unidentified (Venter et al., ).…”

Closing the barrier between disease and health outcomes in Africa through research and capacity development

“…However, African research capacity has not yet reached the levels of that in high-income countries [36]. Although research areas of excellence already existed in the Wits Faculty of Health Sciences, and some of our researchers have contributed extensively to the international body of knowledge around HIV/AIDS, tuberculosis, malaria and drug delivery [see, for example, 37–43], there was a need to strengthen wider areas of research as well as increase the training and support for emergent researchers and postgraduate students in the Faculty. We believed, like Fonn [3], that it was important to initiate these strategies locally and ensure their sustainability.…”

Insecticide Resistance and Its Intensity in Populations of Malaria Vectors in Colombia

“…IRS failure has been observed when the levels of resistance intensity of the local vector populations are high [30]. This is less clear when using LLINs, attributed by some to the personal protection provided by the nets despite high level of vector resistance [31, 32].…”