Dataset Information

Malaria Burden and Associated Risk Factors in an Area of Pyrethroid-Resistant Vectors in Southern Benin.

ABSTRACT: Malaria remains the main cause of morbidity and mortality in Benin despite the scale-up of long-lasting insecticidal nets (LLINs), indoor residual spraying, and malaria case management. This study aimed to determine the malaria burden and its associated risk factors in a rural area of Benin characterized by high net coverage and pyrethroid-resistant mosquito vectors. A community-based cross-sectional survey was conducted in three districts in southern Benin. Approximately 4,320 randomly selected participants of all ages were tested for malaria using rapid diagnostic tests within 60 clusters. Risk factors for malaria infection were evaluated using mixed-effect logistic regression models. Despite high population net use (96%), malaria infection prevalence was 43.5% (cluster range: 15.1-72.7%). Children (58.7%) were more likely to be infected than adults (31.2%), with a higher malaria prevalence among older children (5-10 years: 69.1%; 10-15 years: 67.9%) compared with young children (< 5 years: 42.1%); however, young children were more likely to be symptomatic. High household density, low socioeconomic status, young age (< 15 years), poor net conditions, and low net usage during the previous week were significantly associated with malaria infection. Malaria prevalence remains high in this area of intense pyrethroid resistance despite high net use. New classes of LLINs effective against resistant vectors are therefore crucial to further reduce malaria in this area.

SUBMITTER: Accrombessi M

PROVIDER: S-EPMC9490648 | biostudies-literature | 2022 Jul

REPOSITORIES: biostudies-literature

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Malaria Burden and Associated Risk Factors in an Area of Pyrethroid-Resistant Vectors in Southern Benin.

Accrombessi Manfred M Akogbeto Martin C MC Dangbenon Edouard E Akpovi Hilaire H Sovi Arthur A Yovogan Boulais B Adoha Constantin C Assongba Landry L Ogouyemi-Hounto Aurore A Padonou Germain Gil GG Thickstun Charles C Rowland Mark M Ngufor Corine C Protopopoff Natacha N Cook Jackie J

The American journal of tropical medicine and hygiene 20220718

Malaria remains the main cause of morbidity and mortality in Benin despite the scale-up of long-lasting insecticidal nets (LLINs), indoor residual spraying, and malaria case management. This study aimed to determine the malaria burden and its associated risk factors in a rural area of Benin characterized by high net coverage and pyrethroid-resistant mosquito vectors. A community-based cross-sectional survey was conducted in three districts in southern Benin. Approximately 4,320 randomly selected ...[more]

PMID: 35895353

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Project description:BackgroundCluster-randomized controlled trials (cluster-RCTs) have demonstrated variation in the epidemiological efficacy of different next-generation insecticide-treated net (ITN) types, with some providing shorter-lived impact than others. Further studies are needed to assess changes in the insecticidal durability of these ITNs over time to complement cluster-RCT results.MethodsA series of experimental hut trials were performed to evaluate the bioefficacy of new and field-aged next-generation ITNs (PermaNet® 3.0, Royal Guard®, Interceptor® G2) compared to a pyrethroid-only net (Interceptor®) against pyrethroid-resistant malaria vectors in Covè, southern Benin. Field-aged nets were withdrawn from households at 12, 24 and 36 months. Net pieces cut from whole ITNs were analysed for chemical content, and susceptibility bioassays were performed during each trial to assess changes in insecticide resistance in the Covè vector population.ResultsInterceptor® G2 induced superior mosquito mortality than the other ITNs across all time points. The improved mortality with Interceptor® G2 compared to Interceptor® was evident across all time points but was greater with new nets (odds ratio (OR) = 8.6, 95% CI [7.4, 10.1]) than field-aged nets (OR = 2.5, 95% CI [1.8, 3.5] at 12 months, OR = 2.4, 95% CI [1.6, 3.7] at 24 months and OR = 2.9, 95% CI [1.6, 5.1] at 36 months). New Royal Guard® reduced mosquito fertility compared to the other ITNs, but this improvement fell after field-ageing, particularly at 24 months when it was similar to Interceptor® (11% vs 3%, p = 0.08). When new, mortality was significantly higher with PermaNet® 3.0 compared to Interceptor® (OR = 3.6, 95% CI [3.0, 4.2]); however, this benefit was lost with field-aged nets at 12 months (OR = 1.1, 95% CI [0.8, 1.5]) and 24 months (OR = 0.6, 95% CI [0.4, 0.9]). Retention of the non-pyrethroid compound in next-generation nets was low after 36 months (27% for PermaNet® 3.0, 26% for Royal Guard® and 15% for Interceptor® G2).ConclusionsInterceptor® G2 outperformed the other ITNs, confirming the superiority of pyrethroid-chlorfenapyr nets over other net types. When new, all next-generation ITNs showed superior bioefficacy compared to Interceptor®; however, the size of this improvement fell after field-ageing due to poor durability of the non-pyrethroid compound. These findings emphasize the need to enhance the insecticidal durability of next-generation ITNs.

Project description:BackgroundWhere resources are available, non-pyrethroid IRS can be deployed to complement standard pyrethroid LLINs with the aim of achieving improved vector control and managing insecticide resistance. The impact of the combination may however depend on the type of IRS insecticide deployed. Studies comparing combinations of pyrethroid LLINs with different types of non-pyrethroid IRS products will be necessary for decision making.MethodsThe efficacy of combining a standard pyrethroid LLIN (DuraNet®) with IRS insecticides from three chemical classes (bendiocarb, chlorfenapyr and pirimiphos-methyl CS) was evaluated in an experimental hut trial against wild pyrethroid-resistant Anopheles gambiae s.l. in Cové, Benin. The combinations were also compared to each intervention alone. WHO cylinder and CDC bottle bioassays were performed to assess susceptibility of the local An. gambiae s.l. vector population at the Cové hut site to insecticides used in the combinations.ResultsSusceptibility bioassays revealed that the vector population at Cové, was resistant to pyrethroids (<20% mortality) but susceptible to carbamates, chlorfenapyr and organophosphates (≥98% mortality). Mortality of wild free-flying pyrethroid resistant An. gambiae s.l. entering the hut with the untreated net control (4%) did not differ significantly from DuraNet® alone (8%, p = 0.169). Pirimiphos-methyl CS IRS induced the highest mortality both on its own (85%) and in combination with DuraNet® (81%). Mortality with the DuraNet® + chlorfenapyr IRS combination was significantly higher than each intervention alone (46% vs. 33% and 8%, p<0.05) demonstrating an additive effect. The DuraNet® + bendiocarb IRS combination induced significantly lower mortality compared to the other combinations (32%, p<0.05). Blood-feeding inhibition was very low with the IRS treatments alone (3-5%) but increased significantly when they were combined with DuraNet® (61% - 71%, p<0.05). Blood-feeding rates in the combinations were similar to the net alone. Adding bendiocarb IRS to DuraNet® induced significantly lower levels of mosquito feeding compared to adding chlorfenapyr IRS (28% vs. 37%, p = 0.015).ConclusionsAdding non-pyrethroid IRS to standard pyrethroid-only LLINs against a pyrethroid-resistant vector population which is susceptible to the IRS insecticide, can provide higher levels of vector mosquito control compared to the pyrethroid net alone or IRS alone. Adding pirimiphos-methyl CS IRS may provide substantial improvements in vector control while adding chlorfenapyr IRS can demonstrate an additive effect relative to both interventions alone. Adding bendiocarb IRS may show limited enhancements in vector control owing to its short residual effect.

Project description:BackgroundAggravation of insecticide resistance in malaria vectors is threatening the efforts to control malaria by reducing the efficacy of insecticide-based interventions hence needs to be closely monitored. This study investigated the intensity of insecticide resistance of two major malaria vectors An. funestus sensu stricto (s.s.) and An. gambiae sensu lato (s.l.) collected in southern Ghana and assessed the bio-efficacy of several long-lasting insecticidal nets (LLINs) against these mosquito populations.MethodsThe insecticide susceptibility profiles of Anopheles funestus s.s. and Anopheles gambiae s.l. populations from Obuasi region (Atatam), southern Ghana were characterized and the bio-efficacy of some LLINs was assessed to determine the impact of insecticide resistance on the effectiveness of these tools. Furthermore, molecular markers associated with insecticide resistance in both species were characterized in the F0 and F1 populations using PCR and qPCR methods.ResultsAnopheles funestus s.s. was the predominant species and was resistant to pyrethroids, organochlorine and carbamate insecticides, but fully susceptible to organophosphates. An. gambiae s.l. was resistant to all four insecticide classes. High intensity of resistance to 5 × and 10 × the discriminating concentration (DC) of pyrethroids was observed in both species inducing a considerable loss of efficacy of long-lasting insecticidal nets (LLINs). Temporal expression analysis revealed a massive 12-fold increase in expression of the CYP6P4a cytochrome P450 gene in An. funestus s.s., initially from a fold change of 41 (2014) to 500 (2021). For both species, the expression of candidate genes did not vary according to discriminating doses. An. gambiae s.l. exhibited high frequencies of target-site resistance including Vgsc-1014F (90%) and Ace-1 (50%) while these mutations were absent in An. funestus s.s.ConclusionsThe multiple and high intensity of resistance observed in both malaria vectors highlights the need to implement resistance management strategies and the introduction of new insecticide chemistries.

Project description:BACKGROUND: The dramatic success of insecticide treated nets (ITNs) and long-lasting insecticidal nets (LLINs) in African countries has been countered by the rapid development of pyrethroid resistance in vector mosquitoes over the past decade. One advantage of the use of pyrethroids in ITNs is their excito-repellency. Use of the excito-repellency of pyrethroids might be biorational, since such repellency will not induce or delay the development of any physiological resistance. However, little is known about the relationship between the mode of insecticide resistance and excito-repellency in pyrethroid-resistant mosquitoes. METHODS: Differences in the reactions of 3 major malaria vectors in western Kenya to pyrethroids were compared in laboratory tests. Adult susceptibility tests were performed using World Health Organization (WHO) test tube kits for F1 progenies of field-collected An. gambiae s.s., An. arabiensis, and An. funestus s.s., and laboratory colonies of An. gambiae s.s. and An. arabiensis. The contact repellency to pyrethroids or permethrin-impregnated LLINs (Olyset® Nets) was evaluated with a simple choice test modified by WHO test tubes and with the test modified by the WHO cone bioassay test. RESULTS: Field-collected An. gambiae s.s., An. arabiensis, and An. funestus s.s. showed high resistance to both permethrin and deltamethrin. The allelic frequency of the point mutation in the voltage-gated sodium channel (L1014S) in An. gambiae s.s. was 99.3-100%, while no point mutations were detected in the other 2 species. The frequency of takeoffs from the pyrethroid-treated surface and the flying times without contacting the surface increased significantly in pyrethroid-susceptible An. gambiae s.s. and An. arabiensis colonies and wild An. arabiensis and An. funestus s.s. colonies, while there was no significant increase in the frequency of takeoffs or flying time in the An. gambiae s.s. wild colony. CONCLUSION: A different repellent reaction was observed in the field-collected An. gambiae s.s. than in An. arabiensis and An. funestus s.s. It might be that resistant mosquitoes governed by knockdown resistance (kdr) loose repellency to pyrethroids, whereas those lacking kdr maintain high repellency irrespective of their possessing metabolic resistance factors to pyrethroids. Further genetic evaluation is required for the demonstration of the above hypothesis.

Dataset Information

Malaria Burden and Associated Risk Factors in an Area of Pyrethroid-Resistant Vectors in Southern Benin.

Publications

Malaria Burden and Associated Risk Factors in an Area of Pyrethroid-Resistant Vectors in Southern Benin.

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