Spatial and temporal development of deltamethrin resistance in malaria vectors of the Anopheles gambiae complex from North Cameroon

The effectiveness of insecticide-based malaria vector control interventions in Africa is threatened by the spread and intensification of pyrethroid resistance in targeted mosquito populations. The present study aimed at investigating the temporal and spatial dynamics of deltamethrin resistance in An. gambiae s.l. populations from North Cameroon. Mosquito larvae were collected from 24 settings of the Garoua, Pitoa and Mayo Oulo Health Districts (HDs) from 2011 to 2015. Two to five days old female An. gambiae s.l. emerging from larval collections were tested for deltamethrin resistance using the World Health Organization’s (WHO) standard protocol. Sub samples of test mosquitoes were identified to species using PCR-RFLP and genotyped for knockdown resistance alleles (Kdr 1014F and 1014S) using Hot Ligation Oligonucleotide Assay (HOLA). All the tested mosquitoes were identified as belonging to the An. gambiae complex, including 3 sibling species mostly represented by Anopheles arabiensis (67.6%), followed by Anopheles coluzzii (25.4%) and Anopheles gambiae (7%). Deltamethrin resistance frequencies increased significantly between 2011 and 2015, with mosquito mortality rates declining from 70–85% to 49–73% in the three HDs (Jonckheere-Terstra test statistic (JT) = 5638, P< 0.001), although a temporary increase of mortality rates (91–97%) was seen in the Pitoa and Mayo Oulo HDs in 2012. Overall, confirmed resistance emerged in 10 An. gambiae s.l. populations over the 24 field populations monitored during the study period, from 2011 to 2015. Phenotypic resistance was mostly found in urban settings compared with semi-urban and rural settings (JT = 5282, P< 0.0001), with a spatial autocorrelation between neighboring localities. The Kdr 1014F allelic frequencies in study HDs increased from 0–30% in 2011 to 18–61% in 2014–2015 (JT = 620, P <0.001), especially in An. coluzzii samples. The overall frequency of the Kdr 1014S allele was 0.1%. This study revealed a rapid increase and widespread deltamethrin resistance frequency as well as Kdr 1014F allelic frequencies in An. gambiae s.l. populations over time, emphasizing the urgent need for vector surveillance and insecticide resistance management strategies in Cameroon

Map of Mozambique showing Zambezia province, the study site.

<p>Map of Mozambique showing Zambezia province, the study site.</p

Multivariable logistical regression model of risk factors for malaria infection in Zambezia province.

<p>OR* adjusted for age, year of survey and wealth index. Estimates of OR* for covariates not related with farm animals were done with pig variable in the model.</p><p>*P-value derived from Wald test adjusted for the combine effect of categories in the variable.</p

Developing a spatial-statistical model and map of historical malaria prevalence in Botswana using a staged variable selection procedure-0

<p><b>Copyright information:</b></p><p>Taken from "Developing a spatial-statistical model and map of historical malaria prevalence in Botswana using a staged variable selection procedure"</p><p>http://www.ij-healthgeographics.com/content/6/1/44</p><p>International Journal of Health Geographics 2007;6():44-44.</p><p>Published online 24 Sep 2007</p><p>PMCID:PMC2082025.</p><p></p

Characteristics of surveys included in the analysis.

<p>Characteristics of surveys included in the analysis.</p

Reduction in the odds of malaria infection in children aged 0–5 y sleeping under insecticide-treated nets in sub-Saharan Africa.

<p>Values to the left of the vertical line representing the null value indicate a reduction in the odds of malaria infection in users of insecticide-treated nets compared to non-users. Data are taken from 15 Demographic and Health Surveys and 14 Malaria Indicator Surveys conducted between 2008 and 2015. ORs are adjusted for age, gender, indoor residual spraying in the past 12 mo (where measured), household wealth, house type, and geographic cluster. Summary effects are from random effects analysis. Sub-groups show diagnostic test. Error bars show 95% confidence intervals. DRC, Democratic Republic of the Congo; OR, odds ratio; RDT, rapid diagnostic test.</p

Monthly mean <i>Anopheles</i> density per house in the two arms and rainfall during baseline and post intervention period.

<p>Monthly mean <i>Anopheles</i> density per house in the two arms and rainfall during baseline and post intervention period.</p

Post intervention entomological outcomes by study arm and by low and high density <i>An</i>.<i>gambiae</i> s.l. density stratum at baseline.

<p>¹Odd Ratio (OR), Density Ration (DR) and Incidence Rate Ration (IRR) are adjusted for baseline mean cluster An. gambiae s.l. as categorical with < = 1 An. gambiae s.l./household/night and clusters>1</p><p>²N = Total Anopheles for Sporozoite rates and</p><p>³N total of houses for An. gambiae s.l. density and EIR</p><p>⁴ Interaction p value = p-value for difference between strata</p><p>Post intervention entomological outcomes by study arm and by low and high density <i>An</i>.<i>gambiae</i> s.l. density stratum at baseline.</p

Numbers and prevalence for Rapid Diagnostic Test and anti <i>P.falciaprum</i> AMA-1 antibody positive individuals for each sentinel site in Bioko.

<p>Numbers and prevalence for Rapid Diagnostic Test and anti <i>P.falciaprum</i> AMA-1 antibody positive individuals for each sentinel site in Bioko.</p

Adjusted incidence rate ratio for mean <i>An</i>.<i>gambiae</i> s.l. density per household between ITN arm (reference IRR = 1) and ITN+ IRS arm per light trap collection round.

<p>Adjusted incidence rate ratio for mean <i>An</i>.<i>gambiae</i> s.l. density per household between ITN arm (reference IRR = 1) and ITN+ IRS arm per light trap collection round.</p