Underpinning Sustainable Vector Control through Informed Insecticide Resistance Management

Background: There has been rapid scale-up of malaria vector control in the last ten years. Both of the primary control strategies, long-lasting pyrethroid treated nets and indoor residual spraying, rely on the use of a limited number of insecticides. Insecticide resistance, as measured by bioassay, has rapidly increased in prevalence and has come to the forefront as an issue that needs to be addressed to maintain the sustainability of malaria control and the drive to elimination. Zambia’s programme reported high levels of resistance to the insecticides it used in 2010, and, as a result, increased its investment in resistance monitoring to support informed resistance management decisions. Methodology/Principal Findings: A country-wide survey on insecticide resistance in Zambian malaria vectors was performed using WHO bioassays to detect resistant phenotypes. Molecular techniques were used to detect target-site mutations and microarray to detect metabolic resistance mechanisms. Anopheles gambiae s.s. was resistant to pyrethroids,DDT and carbamates, with potential organophosphate resistance in one population. The resistant phenotypes were conferred by both target-site and metabolic mechanisms. Anopheles funestus s.s. was largely resistant to pyrethroids and carbamates, with potential resistance to DDT in two locations. The resistant phenotypes were conferred by elevated levels of cytochrome p450s. Conclusions/Significance: Currently, the Zambia National Malaria Control Centre is using these results to inform their vector control strategy. The methods employed here can serve as a template to all malaria-endemic countries striving to create a sustainable insecticide resistance management pla

Over expressed annotated genes from gene families involved in detoxification in six vector populations in Zambia according to microarray (FC>2 and corrected p<0.05).

<p>qRT PCR fold change values are presented where available.</p><p>*significantly different than susceptible strain.</p><p>nd not done.</p

Spatiotemporal pattern of insecticide use for IRS in Zambia from 2005–2012.

<p>Each dot represents the insecticide history for a single district or cluster of districts with similar history (Copperbelt Province). The earliest insecticide used is indicated in the centre of each dot. Subsequent insecticides are added as layers, with the thickness of the layer representing how many years the insecticide was used. Different colours represent different insecticide classes. The size of the dot indicates how many years IRS has been active. Hashed areas indicate times and locations where DDT and pyrethroids were used concurrently, with the former on mud homes and the latter on painted surfaces.</p

WHO bioassay test results on 2–5 day old adult mosquitoes from May 2012-April 2013 from 19 districts in Zambia.

<p>WHO bioassay test results on 2–5 day old adult mosquitoes from May 2012-April 2013 from 19 districts in Zambia.</p

Insecticide resistance in collections from March 2011–April 2012.

<p>Darker gray shading indicates areas surveyed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099822#pone.0099822-Chanda2" target="_blank">[16]</a>. *locations with microarray data.</p

WHO bioassay test results on 2–5 day old adult mosquitoes from March 2011-April 2012 from 14 districts in Zambia.

<p>WHO bioassay test results on 2–5 day old adult mosquitoes from March 2011-April 2012 from 14 districts in Zambia.</p

Genotypes of the voltage-gated sodium channel and acetylcholinesterase in <i>An. gambiae s.s.</i> from two locations in Zambia.

<p>F indicates <i>kdr</i> west allele (1014F), L is the susceptible. r is a resistant allele for the <i>Ace-1^R</i> mutation (G119S), and s is susceptible.</p

Prevalence of Plasmodium DNA in the heads/thoraces of wild caught F0 mosquitoes after being held to lay eggs.

<p>The assay does not discriminate between <i>P. ovale</i>, <i>P. vivax</i>, and <i>P. malariae</i>.</p

Over expression of <i>CYP6P9a</i> in <i>An. funestus</i> according to qRT PCR.

<p>The size of the circle represents the relative levels of over expression between populations. Circles bearing the same letters do not have significantly different fold-changes using student's t-test and an alpha of 0.05.</p