Better methods, better data: landscaping the priorities for improving methodologies in vector control.

This article addresses the evolving challenges in evaluating insecticide-based tools for vector control. In response to the emergence of insecticide resistance in major malaria vectors, novel chemistries and products are coming to market, and there is a need to review the available testing methodologies. Commonly used methods for evaluating insecticides, such as the World Health Organization (WHO) cone bioassay, are inadequate for the diverse range of tools now available. Innovation to Impact (I2I) has studied the variability in laboratory methods, with the aim of identifying key factors that contribute to variation and providing recommendations to tighten up protocols. The I2I Methods Landscape is a living document which presents a review of existing methods for evaluating vector control tools, with the scope currently extending to insecticide-treated nets (ITNs) and indoor residual sprays (IRS). The review reveals a lack of validation for many commonly used vector control methods, highlighting the need for improved protocols to enhance reliability and robustness of the data that is generated to make decisions in product development, evaluation, and implementation. A critical aspect highlighted by this work is the need for tailored methods to measure endpoints relevant to the diverse modes of action of novel insecticides. I2I envisage that the Methods Landscape will serve as a decision-making tool for researchers and product manufacturers in selecting appropriate methods, and a means to prioritise research and development. We call for collective efforts in the pro-active development, validation, and consistent implementation of suitable methods in vector control to produce the data needed to make robust decisions.

Malaria control. generating evidence from local to global level

Net Loss? Agrochemicals and Insecticide Resistance in the Fight against Malaria.

Malaria is a major contributor to the global disease burden and a significant impediment to socio-economic development in resource-poor countries. In contrast to improved trends of malaria morbidity and mortality in some parts of the world, malaria has re‐ mained a life threatening disease in many other regions including East Africa because of factors such as weak health systems, growing drug and insecticide resistance, ecological change, climate anomalies, socio-economic factors and changes in land use patterns. On‐ going malaria vector control strategies rely mainly on the use of indoor residual spraying (IRS) and insecticide treated nets (ITNs) which are the primary intervention strategies to reduce malaria burden. The current success in reducing malaria related morbidity and mortality has led to the optimism that elimination of the disease as a public health prob‐ lem may be a realistic objective. Efforts during the last decades enabled access to ITNs in sub-Saharan Africa protecting millions of people at risk of malaria. The number of coun‐ tries that employed IRS as a vector control strategy increased almost by two fold and the percentage of households owing at least one ITN in sub-Saharan Africa is estimated to increase from time to time. Currently, all ITNs are treated with pyrethroids while IRS de‐ pends on pyrethroids, DDT and recently on carbamates. Despite IRS and ITNs are known in reducing malaria incidence, insecticide resistance in malaria vectors threatens the suc‐ cess of malaria control program. Resistance to insecticides has occurred in most arthro‐ pod vectors with different mechanisms. If the current trends of increased insecticide resistance continue, it may jeopardise the efficacy of current vector control tools. Given the limited choice of available insecticides, i.e., only 12 insecticides belonging to 4 classes of insecticides (organochlorines, organophosphates, pyrethroids and carbamates), resist‐ ance to these insecticides has become a limiting factor for current efforts to sustain con‐ trol. Currently, no other insecticide class with similar efficacy has been approved by WHOPES. The development of insecticide resistance in malaria vectors has been attribut‐ ed to the prolonged use of insecticides for IRS and high coverage of ITNs/LLINs. The re‐ cent use of pyrethroids for indoor residual spraying is likely to have enhanced the selection pressure for insecticide resistance alleles among East African vector popula‐ tions. Moreover, mosquitoes breeding in agricultural habitats are exposed to sub lethal © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. doses of pesticides used in agriculture. Since currently recommended insecticides for IRS or ITNs were developed with similar active ingredients of pesticides used for agricultural pest control, their extensive and widespread use to boost agricultural productivity is be‐ lieved to foster insecticide resistance in mosquito populations. There is strong evidence on the emergence of resistance to DDT and pyrethroids in the major malaria vectors in East Africa however, current information on resistance status of the malaria vectors in different areas of the sub-region is scarce. Genes conferring resistance to malaria vectors, including kdr, super kdr and acetylcholinesterase mutations and metabolic resistance are not mapped. The frequency and spatial distribution of East and West African kdr muta‐ tions and their association with the phenotypic resistance in East Africa is less under‐ stood. The bioassay results after WHO diagnostic tests in different East African malaria vector populations against insecticides used in public health is not well documented. In conclusion, planning and implementing insecticide resistance monitoring and manage‐ ment strategy should be part of the vector control program either for pre-emptive action without waiting for the development of resistance or to slowdown the spread of resist‐ ance in malaria vectors in the sub-region.

Malaria remains a significant public health concern in Pakistan due to its subtropical climate and diverse array of vectors, which contribute to periodic outbreaks and challenges in disease control. Recent outbreaks-particularly in 2022-along with the rising incidence of Plasmodium falciparum and growing resistance of Anopheles mosquito vector to existing control methods, highlight a critical gap in understanding the effectiveness of current malaria vector control strategies. This article is a scoping review of published literature on malaria prevention methods with a focus on World Health Organization (WHO) outlined interventions in the endemic region of the lower middle-income country, Pakistan. Relevant articles published in all languages before September 2023 were reviewed. All the articles were obtained from PubMed, Scopus, CINAHL, Embase and Google Scholar. Four independent reviewers performed the selection and characterization of articles based on defined inclusion criteria. The data collected were extracted and analyzed by province, vector, and vector control methods according to WHO recommendations. A total of 46 articles reporting surveillance findings on vector control methods in Pakistan were found. Based on WHO recommendations, the reported strategies included insecticide-treated nets (ITN) (29.79%), indoor residual spraying (IRS) (29.79%), spatial spraying (12.77%), spatial/airborne repellents (4.26%), larval source management (4.26%) and house modifications (4.26%). In contrast to Khyber Pakhtunkhwa, which employs ITN (55%) as the primary vector control method, Punjab was found to use IRS as the main method of vector control (50%). This review highlights the current strategies for controlling malaria vectors and the strategies used in the past for outbreaks in Pakistan. This review identifies a notable increase in the use of insecticide-treated nets (ITNs) over time and highlights differences in the implementation of vector control strategies across provinces in Pakistan. Current practices and their contrast to WHO guidelines are illustrated. It helps us understand the need for improved research and development with precise reporting. These findings can serve as a reference for guiding policy decisions and improving malaria control efforts in endemic regions.

BACKGROUND: Primary malaria prevention on a large scale depends on two vector control interventions: indoor residual spraying (IRS) and insecticide-treated mosquito nets (ITNs). Historically, IRS has reduced malaria transmission in many settings in the world, but the health effects of IRS have never been properly quantified. This is important, and will help compare IRS with other vector control interventions. OBJECTIVES: To quantify the impact of IRS alone, and to compare the relative impacts of IRS and ITNs, on key malariological parameters. SEARCH STRATEGY: We searched the Cochrane Infectious Diseases Group Specialized Register (September 2009), CENTRAL (The Cochrane Library 2009, Issue 3), MEDLINE (1966 to September 2009), EMBASE (1974 to September 2009), LILACS (1982 to September 2009), mRCT (September 2009), reference lists, and conference abstracts. We also contacted researchers in the field, organizations, and manufacturers of insecticides (June 2007). SELECTION CRITERIA: Cluster randomized controlled trials (RCTs), controlled before-and-after studies (CBA) and interrupted time series (ITS) of IRS compared to no IRS or ITNs. Studies examining the impact of IRS on special groups not representative of the general population, or using insecticides and dosages not recommended by the World Health Organization (WHO) were excluded. DATA COLLECTION AND ANALYSIS: Two authors independently reviewed trials for inclusion. Two authors extracted data, assessed risk of bias and analysed the data. Where possible, we adjusted confidence intervals (CIs) for clustering. Studies were grouped into those comparing IRS with no IRS, and IRS compared with ITNs, and then stratified by malaria endemicity. MAIN RESULTS: IRS versus no IRSStable malaria (entomological inoculation rate (EIR) 1): Two studies; for incidence and prevalence, the malaria rates were higher in the IRS group compared to the ITN group in one study. Malaria incidence was higher in the IRS arm in India (risk ratio IRS:ITN = 1.48) and in South Africa (risk ratio 1.34 but the cluster unadjusted CIs included 1). For malaria prevalence, ITNs appeared to give better protection against any infection compared to IRS in India (risk ratio IRS:ITN = 1.70) and also for both P. falciparum (risk ratio IRS:ITN = 1.78) and P. vivax (risk ratio IRS:ITN = 1.37). AUTHORS' CONCLUSIONS: Historical and programme documentation has clearly established the impact of IRS. However, the number of high-quality trials are too few to quantify the size of effect in different transmission settings. The evidence from randomized comparisons of IRS versus no IRS confirms that IRS reduces malaria incidence in unstable malaria settings, but randomized trial data from stable malaria settings is very limited. Some limited data suggest that ITN give better protection than IRS in unstable areas, but more trials are needed to compare the effects of ITNs with IRS, as well as to quantify their combined effects

Laboratory and experimental hut evaluation of mosquito net and indoor residual spray (IRS) insecticides for improved malaria control

Long-lasting insecticidal nets to prevent visceral leishmaniasis in the Indian subcontinent; methodological lessons learned from a cluster randomised controlled trial.

Contact and noncontact behavioral actions of wild-caught Anopheles dirus in response to the operational field dose of three synthetic pyrethroids (bifenthrin, α-cypermethrin and λ-cyhalothrin) were evaluated using an exito-repellency test chamber. DEET was used as the repellency standard for comparison with the other three synthetic pyrethroids. Results showed that test specimens rapidly escaped from the test chamber when exposed to direct contact with a surface treated with each of the three synthetic pyrethroids and DEET. Alpha-cypermethrin demonstrated the strongest irritant action (84.9% escape), followed by DEET (77.0%), λ-cyhalothrin (68.6%) and bifenthrin (68.3%). In the noncontact configuration, fewer mosquitoes escaped from the test chambers as compared to contact trials, although a significant escape response was still observed as compared to the controls (P<0.05). We conclude that An. dirus exhibits both irritant and repellent actions in response the three pyrethroids testing in this study. The information obtained will allow us to better understand the behavioral responses of vectors to various chemicals and provide guidance when designing control strategies for targeting specific disease vectors.

Elimination of visceral leishmaniasis (VL) in Southeast Asia and global control of cutaneous leishmaniasis (CL) and VL are priorities of the World Health Organization (WHO). But is the existing evidence good enough for public health recommendations? This meta-review summarises the available and new evidence for vector control with the aims of establishing what is known about the value of vector control for the control of CL and VL, establishing gaps in knowledge, and particularly focusing on key recommendations for further scientific work. This meta-review follows the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) criteria, including (1) systematic reviews and meta-analyses (SRs/MAs) for (2) vector control methods and strategies and (3) for the control of CL and/or VL. Nine SRs/MAs were included, with different research questions and inclusion/exclusion criteria. The methods analysed for vector control can be broadly classified into (1) indoor residual spraying (IRS); (2) insecticide-treated nets (ITNs; including insecticide-impregnated bednets); (3) insecticide-treated curtains (ITCs; including insecticide-treated house screening); (4) insecticide-treated bedsheets (ITSs) and insecticide-treated fabrics (ITFs; including insecticide-treated clothing) and (5) durable wall lining (treated with insecticides) and other environmental measures to protect the house; (6) control of the reservoir host; and (7) strengthening vector control operations through health education. The existing SRs/MAs include a large variation of different primary studies, even for the same specific research sub-question. Also, the SRs/MAs are outdated, using available information until earlier than 2018 only. Assessing the quality of the SRs/MAs, there is a considerable degree of variation. It is therefore very difficult to summarise the results of the available SRs/MAs, with contradictory results for both vector indices and—if available—human transmission data. Conclusions of this meta-review are that (1) existing SRs/MAs and their results make policy recommendations for evidence-based vector control difficult; (2) further work is needed to establish efficacy and community effectiveness of key vector control methods with specific SRs and MAs (3) including vector and human transmission parameters; and (4) attempting to conclude with recommendations in different transmission scenarios.

As global efforts to control and eliminate malaria intensify, vector control interventions are being extensively deployed in the context of the World Health Organization (WHO)-led integrated vector management (IVM) strategy [1]. Indoor residual spraying (IRS) and insecticide treated nets (ITNs), supplemented by focalized larval source management, have been harnessed for interrupting transmission [2]. Unfortunately, the efficacy of both IRS and ITNs risks to be markedly undermined by the selection of insecticide resistance in major malaria vectors [3] and their increasing behavioural shifts towards more exophilic, zoophic and/or exophagic and crepuscular-biting tendencies [4]. It is critical for malaria vector control programmes to establish vector surveillance systems that monitor spatio-temporal changes in vector behaviour and biology in order to guide deployment of vector control tools.

BackgroundAchieving vector control targets is a key step towards malaria elimination. Because of variations in reporting of progress towards vector control targets in 2013, the coverage of these vector control interventions in Namibia was assessed.MethodsData on 9846 households, representing 41,314 people, collected in the 2013 nationally-representative Namibia Demographic and Health Survey were used to explore the coverage of two vector control methods: indoor residual spraying (IRS) and insecticide-treated nets (ITNs). Regional data on Plasmodium falciparum parasite rate in those aged 2–10 years (PfPR2–10), obtained from the Malaria Atlas Project, were used to provide information on malaria transmission intensity. Poisson regression analyses were carried out exploring the relationship between household interventions and PfPR2–10, with fully adjusted models adjusting for wealth and residence type and accounting for regional and enumeration area clustering. Additionally, the coverage as a function of government intervention zones was explored and models were compared using log-likelihood ratio tests.ResultsIntervention coverage was greatest in the highest transmission areas (PfPR2–10 ≥ 5%), but was still below target levels of 95% coverage in these regions, with 27.6% of households covered by IRS, 32.3% with an ITN and 49.0% with at least one intervention (ITN and/or IRS). In fully adjusted models, PfPR2–10 ≥ 5% was strongly associated with IRS (RR 14.54; 95% CI 5.56–38.02; p < 0.001), ITN ownership (RR 5.70; 95% CI 2.84–11.45; p < 0.001) and ITN and/or IRS coverage (RR 5.32; 95% CI 3.09–9.16; p < 0.001).ConclusionsThe prevalence of IRS and ITN interventions in 2013 did not reflect the Namibian government intervention targets. As such, there is a need to include quantitative monitoring of such interventions to reliably inform intervention strategies for malaria elimination in Namibia.

BackgroundAfrican countries are scaling up malaria interventions, especially insecticide treated nets (ITN) and indoor residual spraying (IRS), for which ambitious coverage targets have been set. In spite of these efforts infection prevalence remains high in many parts of the continent. This study investigated risk factors for malaria infection in children using three malaria indicator surveys from Zambezia province, Mozambique. The impact of IRS and ITNs, the effects of keeping farm animals and of the construction material of roofs of houses and other potential risk factors associated with malaria infection in children were assessed.MethodsCross-sectional community-based surveys were conducted in October of 2006, 2007 and 2008. A total of 8338 children (ages 1–15 years) from 2748 households were included in the study. All children were screened for malaria by rapid diagnostic tests. Caregiver interviews were used to assess household demographic and wealth characteristics and ITN and IRS coverage. Associations between malaria infection, vector control interventions and potential risk factors were assessed.ResultsOverall, the prevalence of malaria infection was 47.8% (95%CI: 38.7%–57.1%) in children 1–15 years of age, less than a quarter of children (23.1%, 95%CI: 19.1%–27.6%) were sleeping under ITN and almost two thirds were living in IRS treated houses (coverage 65.4%, 95%CI: 51.5%–77.0%). Protective factors that were independently associated with malaria infection were: sleeping in an IRS house without sleeping under ITN (Odds Ratio (OR) = 0.6; 95%CI: 0.4–0.9); additional protection due to sleeping under ITN in an IRS treated house (OR = 0.5; 95%CI: 0.3–0.7) versus sleeping in an unsprayed house without a ITN; and parental education (primary/secondary: OR = 0.6; 95%CI: 0.5–0.7) versus parents with no education. Increased risk of infection was associated with: current fever (OR = 1.2; 95%CI: 1.0–1.5) versus no fever; pig keeping (OR = 3.2; 95%CI: 2.1–4.9) versus not keeping pigs; living in houses with a grass roof (OR = 1.7; 95%CI: 1.3–2.4) versus other roofing materials and bigger household size (8–15 people: OR = 1.6; 95%CI: 1.3–2.1) versus small households (1–4 persons).ConclusionMalaria infection among children under 15 years of age in Zambezia remained high but conventional malaria vector control methods, in particular IRS, provided effective means of protection. Household ownership of farm animals, particularly pigs, and living in houses with a grass roof were independently associated with increased risk of infection, even after allowing for household wealth. To reduce the burden of malaria, national control programs need to ensure high coverage of effective IRS and promote the use of ITNs, particularly in households with elevated risks of infection, such as those keeping farm animals, and those with grass roofs.

Brian Leslie Sharp

Indoor residual spray (IRS) and long-lasting insecticidal nets are the two principal intervention methods of vector control. Zero vector durable lining (ZVDL), a relatively new vector control method, was evaluated to assess its efficacy against malaria vectors in hard to reach areas in the Balaghat district, where malaria transmission is perennial. ZVDL was installed in six experimental villages during November-December 2012. In control villages, IRS was carried out with Alphacypermethrin. Cone bioassays were performed to assess the efficacy and persistence of insecticide-treated ZVDL following WHO bioassays. The mean per man hour density of Anopheles caught during 2013 was 12.1 in experimental villages and 16.2 in control villages. No sporozoite-positive Anopheles culicifacies were found in experimental villages; however, in control villages, four sporozoite-positive A. culicifacies were found (two Plasmodium vivax and two P. falciparum). The knock-down rate of A. culicifacies was 95-100% with 100% mortality during the 24 h recovery period. Malaria declined sharply in experimental villages showing a slide positivity rate of 22.3% compared with control villages (36.4%) (p<0.05). A supplementary vector control intervention such as ZVDL has the potential to become a viable alternative to IRS in malaria endemic areas.