Dataset Information

The Impact of Periodic Distribution Campaigns of Long-Lasting Insecticidal-Treated Bed Nets on Malaria Vector Dynamics and Human Exposure in Dielmo, Senegal.

ABSTRACT: The implementation of long-lasting insecticidal-treated bed nets (LLINs) has contributed to halving the mortality rate due to malaria since 2000 in sub-Saharan Africa. These tools are highly effective against indoor-feeding malaria vectors. Thus, to achieve the World Health Assembly's new target to reduce the burden of malaria over the next 15 years by 90%, it is necessary to understand how the spatiotemporal dynamics of malaria vectors and human exposure to bites is modified in the context of scaling up global efforts to control malaria transmission. This study was conducted in Dielmo, a Senegalese village, after the introduction of LLINs and two rounds of LLINs renewals. Data analysis showed that implementation of LLINs correlated with a significant decrease in the biting densities of the main malaria vectors, Anopheles gambiae s.l. and Anopheles funestus, reducing malaria transmission. Other environment factors likely contributed to the decrease in An. funestus, but this trend was enhanced with the introduction of LLINs. The bulk of bites occurred during sleeping hours, but the residual vector populations of An. gambiae s.l. and An. funestus had an increased propensity to bite outdoors, so a risk of infectious bites remained for LLINs users. These results highlight the need to increase the level and correct use of LLINs and to combine this intervention with complementary control measures against residual exposure, such as spatial repellents and larval source management, to achieve the goal of eliminating malaria transmission.

SUBMITTER: Sougoufara S

PROVIDER: S-EPMC5953348 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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The Impact of Periodic Distribution Campaigns of Long-Lasting Insecticidal-Treated Bed Nets on Malaria Vector Dynamics and Human Exposure in Dielmo, Senegal.

Sougoufara Seynabou S Thiaw Omar O Cailleau Aurélie A Diagne Nafissatou N Harry Myriam M Bouganali Charles C Sembène Pape M PM Doucoure Souleymane S Sokhna Cheikh C

The American journal of tropical medicine and hygiene 20180315 5

The implementation of long-lasting insecticidal-treated bed nets (LLINs) has contributed to halving the mortality rate due to malaria since 2000 in sub-Saharan Africa. These tools are highly effective against indoor-feeding malaria vectors. Thus, to achieve the World Health Assembly's new target to reduce the burden of malaria over the next 15 years by 90%, it is necessary to understand how the spatiotemporal dynamics of malaria vectors and human exposure to bites is modified in the context of s ...[more]

PMID: 29557325

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Project description:BACKGROUND:Long-lasting insecticidal nets (LLINs) are the most widely deployed vector control intervention in sub-Saharan Africa to prevent malaria. Recent reports indicate selection of pyrethroid insecticide resistance is widespread in mosquito vectors. This paper explores risk factors associated with malaria infection prevalence and vector density between mass distribution campaigns, changes in net coverage, and loss of protection in an area of high pyrethroid resistance in Northwest Tanzania. METHODS:A cross sectional malaria survey of 3456 children was undertaken in 2014 in Muleba district, Kagera region west of Lake Victoria. Vector density was assessed using indoor light traps and outdoor tent traps. Anophelines were identified to species using PCR and tested for Plasmodium falciparum circumsporozoite protein. Logistic regression was used to identify household and environmental factors associated with malaria infection and regression binomial negative for vector density. RESULTS:LLIN use was 27.7%. Only 16.9% of households had sufficient nets to cover all sleeping places. Malaria infection was independently associated with access to LLINs (OR: 0.57; 95% CI 0.34-0.98). LLINs less than 2 years old were slightly more protective than older LLINs (53 vs 65% prevalence of infection); however, there was no evidence that LLINs in good condition (hole index?<?65) were more protective than LLINs, which were more holed. Other risk factors for malaria infection were age, group, altitude and house construction quality. Independent risk factors for vector density were consistent with malaria outcomes and included altitude, wind, livestock, house quality, open eaves and LLIN usage. Indoor collections comprised 4.6% Anopheles funestus and 95.4% Anopheles gambiae of which 4.5% were Anopheles arabiensis and 93.5% were Anopheles gambiae sensu stricto. CONCLUSION:Three years after the mass distribution campaign and despite top-ups, LLIN usage had declined considerably. While children living in households with access to LLINs were at lower risk of malaria, infection prevalence remained high even among users of LLINs in good condition. While effort should be made to maintain high coverage between campaigns, distribution of standard pyrethroid-only LLINs appears insufficient to prevent malaria transmission in this area of intense pyrethroid resistance.

Project description:BackgroundNigeria carries the greatest malaria burden among countries in the world. As part of the National Malaria Control Strategic Plan, free long-lasting insecticidal nets (LLINs) were distributed in 14 states of Nigeria through mass campaigns led by different organizations (the World Bank, UNICEF, or the Global Fund) between May 2009 and August 2010. The objective of this study was to evaluate the association between LLIN distribution campaigns and child malaria in Nigeria.MethodsData were from the Nigeria Malaria Indicator Survey which was carried out from October to December 2010 on a nationally representative sample of households. Participants were women aged 15-49 years and their children aged less than five years (N?=?4082). The main outcome measure was the presence or absence of malaria parasites in blood samples of children (6-59 months).ResultsCompared with children living in communities with no campaigns, those in the campaign areas were less likely to test positive for malaria after adjusting for geographic locations, community- and individual-level characteristics including child-level use of insecticide-treated nets (ITNs). The protective effects were statistically significant for the World Bank Booster Project areas (OR?=?0.18, 95% CI?=?0.04-0.73) but did not reach statistical significance for other campaign areas. Results also showed that community-level wealth (OR?=?0.51, 95% CI?=?0.34-0.76), community-level maternal knowledge regarding malaria prevention (OR?=?0.70, 95% CI?=?0.50-0.97), and child-level use of ITNs (OR?=?0.79, 95% CI?=?0.63-0.99) were negatively associated with child malaria.ConclusionsThe observed protective effects on child malaria of these campaigns (statistically significant in the World Bank Booster Project areas and non-significant in the other areas) need to be corroborated by future effectiveness studies. Results also show that improving community-level maternal knowledge through appropriate channels might be helpful in preventing child malaria in Nigeria.

Project description:Mosquitoes belonging to the Anopheles gambiae complex are the main vectors of malaria in sub-Saharan Africa. Among these, An. gambiae, Anopheles coluzzii and Anopheles arabiensis are the most efficient vectors and are largely distributed in sympatric locations. However, these species present ecological and behavioural differences that impact their vectorial capacity and complicate vector-control efforts, mainly based on long-lasting insecticidal bed nets (LLINs) and indoor residual spraying (IRS). In this study, the genetic structure of these three species in a Senegalese village (Dielmo) was investigated using microsatellite data in samples collected in 2006 before implementation of LLINs, in 2008, when they were introduced, and in 2010, 2 years after the use of LLINs.In this study 611 individuals were included, namely 136 An. coluzzii, 101 An. gambiae, 6 An. coluzzii/An. gambiae hybrids and 368 An. arabiensis. According to the species, the effect of the implementation of LLINs in Dielmo is differentiated. Populations of the sister species An. coluzzii and An. gambiae regularly experienced bottleneck events, but without significant inbreeding. The Fst values suggested in 2006 a breakdown of assortative mating resulting in hybrids, but the introduction of LLINs was followed by a decrease in the number of hybrids. This suggests a decrease in mating success of hybrids, ecological maladaptation, or a lesser probability of mating between species due to a decrease in An. coluzzii population size. By contrast, the introduction of LLINs has favoured the sibling species An. arabiensis. In this study, some spatial and temporal structuration between An. arabiensis populations were detected, especially in 2008, and the higher genetic diversity observed could result from a diversifying selection.This work demonstrates the complexity of the malaria context and shows the need to study the genetic structure of Anopheles populations to evaluate the effectiveness of vector-control tools and successful management of malaria vector control.

Project description:Malaria control today is threatened by widespread insecticide resistance in vector populations. The World Health Organization (WHO) recommends the use of a mixture of unrelated insecticides for indoor residual spraying (IRS) and long-lasting insecticidal nets (LNs) or as a combination of interventions for improved vector control and insecticide resistance management. Studies investigating the efficacy of these different strategies are necessary.The efficacy of Interceptor® G2 LN, a newly developed LN treated with a mixture of chlorfenapyr (a pyrrole) and alpha-cypermethrin (a pyrethroid), was compared to a combined chlorfenapyr IRS and Interceptor® LN (a standard alpha-cypermethrin LN) intervention in experimental huts in Cove Southern Benin, against wild, free-flying, pyrethroid-resistant Anopheles gambiae s.l. A direct comparison was also made with a pyrethroid-only net (Interceptor® LN) alone and chorfenapyr IRS alone.WHO resistance bioassays performed during the trial demonstrated a pyrethroid resistance frequency of >90% in the wild An. gambiae s.l. from the Cove hut site. Mortality in the control (untreated net) hut was 5%. Mortality with Interceptor® LN (24%) was lower than with chlorfenapyr IRS alone (59%, P < 0.001). The combined Interceptor® LN and chlorfenapyr IRS intervention and the mixture net (Interceptor® G2 LN) provided significantly higher mortality rates (73 and 76%, respectively) and these did not differ significantly between both treatments (P = 0.15). Interceptor LN induced 46% blood-feeding inhibition compared to the control untreated net, while chlorfenapyr IRS alone provided none. Both mixture/combination strategies also induced substantial levels of blood-feeding inhibition (38% with combined interventions and 30% with Interceptor® G2 LN). A similar trend of improved mortality of pyrethroid-resistant An. gambiae s.l. from Cove was observed with Interceptor® G2 LN (79%) compared to Interceptor LN (42%, P < 0.001) in WHO tunnel tests.The use of chlorfenapyr and alpha-cypermethrin together as a mixture on nets (Interceptor® G2 LN) or a combined chlorfenapyr IRS and pyrethroid LN intervention provides improved control of pyrethroid-resistant malaria vectors by inducing significantly higher levels of mortality through the chlorfenapyr component and providing personal protection through the pyrethroid component. Both strategies are comparable in their potential to improve the control of malaria transmitted by pyrethroid resistant mosquito vectors.

Project description:BackgroundScale-up of insecticide-based interventions has averted more than 500 million malaria cases since 2000. Increasing insecticide resistance could herald a rebound in disease and mortality. We aimed to investigate whether insecticide resistance was associated with loss of effectiveness of long-lasting insecticidal nets and increased malaria disease burden.MethodsThis WHO-coordinated, prospective, observational cohort study was done at 279 clusters (villages or groups of villages in which phenotypic resistance was measurable) in Benin, Cameroon, India, Kenya, and Sudan. Pyrethroid long-lasting insecticidal nets were the principal form of malaria vector control in all study areas; in Sudan this approach was supplemented by indoor residual spraying. Cohorts of children from randomly selected households in each cluster were recruited and followed up by community health workers to measure incidence of clinical malaria and prevalence of infection. Mosquitoes were assessed for susceptibility to pyrethroids using the standard WHO bioassay test. Country-specific results were combined using meta-analysis.FindingsBetween June 2, 2012, and Nov 4, 2016, 40 000 children were enrolled and assessed for clinical incidence during 1·4 million follow-up visits. 80 000 mosquitoes were assessed for insecticide resistance. Long-lasting insecticidal net users had lower infection prevalence (adjusted odds ratio [OR] 0·63, 95% CI 0·51-0·78) and disease incidence (adjusted rate ratio [RR] 0·62, 0·41-0·94) than did non-users across a range of resistance levels. We found no evidence of an association between insecticide resistance and infection prevalence (adjusted OR 0·86, 0·70-1·06) or incidence (adjusted RR 0·89, 0·72-1·10). Users of nets, although significantly better protected than non-users, were nevertheless subject to high malaria infection risk (ranging from an average incidence in net users of 0·023, [95% CI 0·016-0·033] per person-year in India, to 0·80 [0·65-0·97] per person year in Kenya; and an average infection prevalence in net users of 0·8% [0·5-1·3] in India to an average infection prevalence of 50·8% [43·4-58·2] in Benin).InterpretationIrrespective of resistance, populations in malaria endemic areas should continue to use long-lasting insecticidal nets to reduce their risk of infection. As nets provide only partial protection, the development of additional vector control tools should be prioritised to reduce the unacceptably high malaria burden.FundingBill & Melinda Gates Foundation, UK Medical Research Council, and UK Department for International Development.

Project description:BackgroundUp until the present, pyrethroid-treated bed nets have been a key tool for vector control in the fight against malaria. A global system that sets standards and facilitates procurement has successfully driven down the price of these bed nets to enable more of them to be distributed. As a result of their mass rollout, malaria cases have been significantly reduced, but pyrethroid resistance is now widespread. Going forward, new insecticides have been and continue to be developed for use on bed nets, but it is unclear how to best deploy them for maximum impact.MethodsHere, an app for the optimization of bed nets based on their insecticide loading concentration and deployment lifespan is presented. Underlying the app are simple models that incorporate the chemical and physical properties of bed nets, and the genetic and ecological properties of resistance evolution in mosquitoes. Where possible, default parameter values are fitted from experimental data. The app numerically searches across a massive number of these simple models with variable loading and lifespan to find their optima under different criteria that constrain the options for vector control.ResultsThe app is not intended to provide a definite answer about the best bed net design, but allows for the quantative exploration of trade-offs and constraints under different conditions. Here, results for the deployment of a new insecticide are explored under default parameter values across public health budgets for the purchase of bed nets. Optimization can lead to substantial gains in the average control of the mosquito population, and these gains are comparatively greater with lower budgets. Whilst optimizing a bed net within the constraints of the incentives of the existing system of standards and procurement leads to substantially greater control than not optimizing the bed net, optimizing the bed net without constraints leads to yet substantially greater control. The most important factor in this optimization is coverage, which depends on the price per bed net. With this in mind, it is unsurprising that the optimization for plausible budgets suggests that a pyrethroid would be the preferred partner for a new insecticide under current constraints because it is cost-effective in the balance of being less expensive than the new insecticide but also less effective due to pre-existing resistance. Surprisingly, a pyrethroid is shown to be an effective partner for a new insecticide in this model because of its contribution to resistance management in delaying the onset of resistance to the new insecticide.ConclusionsThis study highlights the importance of trade-offs in the design of bed nets for vector control. Further, it suggests that there are challenges in the roll-out of bed nets with new insecticides because of the constraints imposed by the global system of standards and procurement, which currently fails to adequately incentivize important considerations in bed net design like resistance management.

Project description:Uganda is conducting a second mass LLIN distribution campaign and Katakwi district recently received LLINs as part of this activity. This study was conducted to measure the success of the campaign in this setting, an area of high transmission, with the objectives to estimate LLIN ownership, access and use pre and post campaign implementation.Two identical cross sectional surveys, based on the Malaria Indicator Survey methodology, were conducted in three sub-counties in this district (Kapujan, Magoro and Toroma), six months apart, one before and another after the mass distribution campaign. Data on three main LLIN indicators including; household LLIN ownership, population with access to an LLIN and use were collected using a household and a women's questionnaire identical to the Malaria Indicator Survey.A total of 601 and 607 households were randomly selected in survey one and two respectively. At baseline, 60.57% (56.53-64.50) of households owned at least one net for every two persons who stayed in the household the night before the survey which significantly increased to 70.35% (66.54-73.96) after the campaign (p = 0.001). Similarly, the percentage of the household population with access to an LLIN significantly increased from 84.76% (82.99-86.52) to 91.57% (90.33-92.81), p = 0.001 and the percentage of household population that slept under an LLIN the night before the survey also significantly increased from 56.85% (55.06-58.82) to 81.72% (76.75-83.21), p = 0.001.The LLIN mass campaign successfully achieved the national target of over eighty-five percent of the population with access to an LLIN in this setting, however, universal household coverage and use were fourteen and three percent points less than the national target respectively. This is useful for malaria programs to consider during the planning of future campaigns by tailoring efforts around deficient areas like mechanisms to increase universal coverage and behavior change communication.

Dataset Information

The Impact of Periodic Distribution Campaigns of Long-Lasting Insecticidal-Treated Bed Nets on Malaria Vector Dynamics and Human Exposure in Dielmo, Senegal.

Publications

The Impact of Periodic Distribution Campaigns of Long-Lasting Insecticidal-Treated Bed Nets on Malaria Vector Dynamics and Human Exposure in Dielmo, Senegal.

Similar Datasets

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