Indoor Residual Insecticide Research Articles

Impact of Indoor Residual Spray (IRS) and Insecticide Treated Nets (ITNs) for sand flies (Diptera: Psychodidae) elimination in some remote communities

Impact of Indoor Residual Spray (IRS) and Insecticide Treated Nets (ITNs) for sand flies (Diptera: Psychodidae) elimination in some remote communities

Targeted indoor residual insecticide applications shift Aedes aegypti age structure and arbovirus transmission potential

While residual insecticide applications have the potential to decrease pathogen transmission by reducing the density of vectors and shifting the age structure of the adult mosquito population towards younger stages of development, this double entomological impact has not been documented for Aedes aegypti. Aedes collected from households enrolled in a cluster-randomized trial evaluating the epidemiological impact of targeted indoor residual spraying (TIRS) in Merida, Mexico, were dissected and their age structure characterized by the Polovodova combined with Christopher’s ovariole growth methods. In total, 813 females were dissected to characterize age structure at 1, 3, 6, and 9 months post-TIRS. Significant differences in the proportion of nulliparous Ae. aegypti females between the treatment groups was found at one-month post-TIRS (control: 35% vs. intervention: 59%), three months (20% vs. 49%) but not at six or nine months post-TIRS. TIRS significantly shiftted Ae. aegypti age structure towards younger stages and led to a non-linear reduction in survivorship compared to the control arm. Reduced survivorship also reduced the number of arbovirus transmitting females (those who survived the extrinsic incubation period). Our findings provide strong evidence of the full entomological impact of TIRS, with important implications for quantifying the epidemiological impact of vector control methods.

Residual insecticide surface treatment for preventing malaria: a systematic review protocol

IntroductionMalaria presents a significant global public health burden, although substantial progress has been made, with vector control initiatives such as indoor residual surface spraying with insecticides and insecticide-treated nets. There now exists many different approaches to apply residual insecticide to indoor and outdoor surfaces in malaria-endemic settings, although no comprehensive systematic reviews exist evaluating these interventions. This manuscript outlines the protocol for a systematic review which aims to synthesise the best available evidence regarding full or partial indoor or outdoor residual insecticide surface treatment for preventing malaria.Methods and analysisThis review will comprehensively search the literature (both published and unpublished) for any studies investigating the effectiveness of residual insecticide surface treatment for malaria. Studies will be screened to meet the inclusion criteria by a minimum of two authors, followed by assessment of risk of bias (using appropriate risk-of-bias tools for randomised and non-randomised studies) and extraction of relevant information using structured forms by two independent authors. Meta-analysis will be carried out where possible for epidemiological outcomes such as malaria, anaemia, malaria-related mortality, all-cause mortality and adverse effects. Certainty in the evidence will be established with GRADE assessments.Ethics and disseminationA full review report will be submitted to the Vector Control & Insecticide Resistance Unit, Global Malaria Program, WHO. A version of this report will be submitted for publication in an open access peer-reviewed journal. The report will inform the development of WHO recommendations regarding residual insecticide treatment for malaria. This systematic review does not require ethics approval as it is a review of primary studies.Systematic review registrationPROSPERO 293194.

Integrated malaria prevention in low- and middle-income countries: a systematic review

BackgroundAs many countries aim to eliminate malaria, use of comprehensive approaches targeting the mosquito vector and environment are needed. Integrated malaria prevention advocates the use of several malaria prevention measures holistically at households and in the community. The aim of this systematic review was to collate and summarize the impact of integrated malaria prevention in low- and middle-income countries on malaria burden.MethodsLiterature on integrated malaria prevention, defined as the use of two or more malaria prevention methods holistically, was searched from 1st January 2001 to 31st July 2021. The primary outcome variables were malaria incidence and prevalence, while the secondary outcome measures were human biting and entomological inoculation rates, and mosquito mortality.ResultsA total of 10,931 studies were identified by the search strategy. After screening, 57 articles were included in the review. Studies included cluster randomized controlled trials, longitudinal studies, programme evaluations, experimental hut/houses, and field trials. Various interventions were used, mainly combinations of two or three malaria prevention methods including insecticide-treated nets (ITNs), indoor residual spraying (IRS), topical repellents, insecticide sprays, microbial larvicides, and house improvements including screening, insecticide-treated wall hangings, and screening of eaves. The most common methods used in integrated malaria prevention were ITNs and IRS, followed by ITNs and topical repellents. There was reduced incidence and prevalence of malaria when multiple malaria prevention methods were used compared to single methods. Mosquito human biting and entomological inoculation rates were significantly reduced, and mosquito mortality increased in use of multiple methods compared to single interventions. However, a few studies showed mixed results or no benefits of using multiple methods to prevent malaria.ConclusionUse of multiple malaria prevention methods was effective in reducing malaria infection and mosquito density in comparison with single methods. Results from this systematic review can be used to inform future research, practice, policy and programming for malaria control in endemic countries.

Evolution of Plasmodial Infection According to Age and Vector Control Method Implemented: Deltamethrin Treated Durable Lining (δDL) in Candiero or Lambdacyhalothrin Indoor Residual Spraying (λIRS) in Chisséquélé, 2 Villages around Balombo Town, Benguela Province, Angola

Several hundred millions of malaria cases were averted these last decades thanks to the large scale implementation of vector control, mainly Long Lasting Insecticide Treated Nets (“LLINs”) and Indoor Residual Spraying (“IRS”).
 Due to several operational issues IRS were stopped in Angola and the National Malaria Control Program (NMCP) is based upon large scale distribution of Long Lasting Insecticide Treated Nets (LLIN) through different channels.
 On the other hand the recently developped Insecticide Treated Plastic Sheeting (ITPS) could represent an interesting alternative to IRS in term of longer lasting activity, community acceptability and participation, entomological and epidemiological efficacy observed in various experimental and natural conditions. Actually the acceptability of ITPS was studied in Huambo, a town close to Balombo but not yet its epidemiological efficacy in this area.
 The aim of the present study was to compare the efficacy of the 2 methods of vector control: Indoor Residual Spraying and Insecticide Treated Plastic Sheeting with 2 parasitological indicators of plasmodial infection: parasite index (“PI”) and parasite load (“PL”) in 2 villages close to Balombo: Candiero, which received 2 rounds of λIRS then δITPS; and Chisséquélé , which received δITPS only and just once; considering 4 age groups recommended in Essential Malariology: 0-2 years old; 3-5 years old; 6-9 years old and 10-15 years old.
 During the 5 five consecutive years of the study, 46 cross sectional parasitological surveys were regularly done (23 in each village), 4792 thick blood films (“TBF”) were prepared and their microscopical examination revealed the presence of plasmodial infections in 925 i.e. an overall Plasmodial Index of 19.3%.
 Plasmodium were noticed in 475 of the 2513 TBF (PI=18.9%) made in Candiero and 450 of the 2279 TBF done in Chisséquélé (PI=19.7%) (χ2= 0.55: P= 0.46; OR= 0.95 [0.82-1.09]).
 Before vector control (VC) Parasite Index (“PI”) of babies (≤ 2 years old) were significantly lower than PI of the three other older age groups. The impact of VC on plasmodial index was different according to age groups. After VC the overall parasite index significantly dropped by #70% in Candiero (IRS village) and # 60% in Chisséquélé (ITPS village), the decrease was significant in each age group but it was less in babies than in the 3 older groups. This could lead to a “negative” conclusion of the efficacy of VC if targeting only plasmodial prevalence in babies.
 On the other hand Parasite Load (“PL”) significantly dropped the first year after VC in babies in the 2 villages and not in all older age group leading to a positive conclusion of the efficacy of VC when targeting babies; the drop of PL after VC was noticed in some age groups (but not all) in Candiero but not in Chisséquélé.
 These analyzes underlined the key issues of the choice of indicator and the targeted age groups because conclusion of the efficacy of one or the other method of vector control could be opposite. Another key point is that, considering the classical age groups (0-5 or 2-9 or ≤15 years old) Insecticide treated plastic sheeting appeared as efficient as Indoor Residual Spraying with the double advantage of lasting longer and involving actual community participation.
 ITPS could therefore be recommended in place of IRS which have well known great operational and social issues.

Residual efficacy of Fludora Fusion against Anopheles arabiensis in simple huts in Ethiopia.

Emergence and spread of malaria vectors resistant to the available insecticides required a new and efficacious insecticide. Residual efficacy of Fludora® Fusion was evaluated against insecticide susceptible Anopheles arabiensis in ten circular huts similar to the residential huts. Fludora® Fusion WP-SB 56.25, FICAM WP80 and Clothianidin WG70 were sprayed, by experienced technician, on interior wall surfaces: paint, dung, smooth mud, and rough mud. WHO cone bioassays were carried out a month after spraying and thereafter on monthly intervals for 12 months. Knockdown was recorded at 60 minutes and mortality at 24 hours, 48 hours and 72 hours holding time post-exposure. Fludora Fusion induced 100% An. arabiensis mortality during the first four months post-treated on all surface types at 24 hours holding time post-exposure. Its activity remained over 80% from the fifth to the twelfth month post-treated on the surfaces with the exception of two assessment points, at seventh month and eleventh month, on paint and smooth mud surfaces. FICAM induced 100% mortality rate during the first 4 months and 92% mortality during the fifth month post-treatment on painted surfaces. Its activity was over 96% mortality 1-month post-treatment on smooth mud and rough mud surfaces and 92% mortality 2-month post-treatment on dung surfaces. Clothianidin caused 89% and 86% mortality 1-month post-treatment on smooth mud and rough mud surfaces. Fludora Fusion can be used as alternative indoor residual insecticide spraying against An. arabiensis in Ethiopia.

Temporal Evaluation of Insecticide Resistance in Populations of the Major Arboviral Vector Aedes Aegypti from Northern Nigeria.

Simple SummaryOutbreaks of dengue and yellow fever are fast becoming normal in Nigeria. Transmitted by mosquito vectors, Aedes aegypti and/or Aedes albopictus, control of these arboviral diseases depends largely on control of the above vectors. This requires knowledge of the identity/composition and insecticide resistance profile of the vector species—knowledge which is inadequate across Nigeria. In this study we characterised two populations of Aedes aegypti from north-western Nigeria (BUK/Kano and Pantami). Bioassays with Kano larvae suggest resistance to temephos (an important insecticide for larval control) is low but increasing, while deltamethrin resistance is high, and increased 6-fold between 2018 and 2019, and 11-fold by 2020. Adult bioassays established high pyrethroid resistance (the bed net insecticides) and extreme resistance to DDT (an indoor residual spraying insecticide). Bioassays with piperonylbutoxide and diethylmaleate (synergists which block activity of the enzymes that confer insecticide resistance) resulted in significant recovery of mortalities, implicating CYP450s and GSTs—enzymes which confer pyrethroid and DDT resistance, respectively. Tests with pyrethroid-containing bed net, PermaNet® 3.0 (side panels) revealed high resistance, in contrast to the areas also containing piperonylbutoxide (PermaNet® 3.0, roof panel). These findings highlight the challenges associated with the control of this arboviral vector of public health importance in Nigeria.To support evidence-based control measures, two Nigerian Aedes populations (BUK and Pantami) were characterised. Larval bioassay using temephos and deltamethrin revealed a significant increase in deltamethrin resistance, with LC50 of 0.018mg/L (resistance ratio compared to New Orleans, RR = 2.250) in 2018 increasing ~6-fold, by 2019 (LC50 = 0.100mg/L, RR = 12.5), and ~11-fold in 2020 (LC50 = 0.198mg/L, RR = 24.750). For the median deltamethrin concentration (0.05mg/L), a gradual decrease in mortality was observed, from 50.6% in 2018, to 44.9% in 2019, and 34.2% in 2020. Extremely high DDT resistance was observed, with <3% mortalities and LT50s of 352.87 min, 369.19 min and 406.94 min in 2018, 2019 and 2020, respectively. Significant temporal increase in resistance was observed towards ƛ-cyhalothrin (a type II pyrethroid) over three years. Synergist bioassays with diethylmaleate and piperonylbutoxide significantly recovered DDT and ƛ-cyhalothrin susceptibility respectively, implicating glutathione S-transferases and CYP450s. Cone bioassays revealed increased resistance to the PermaNet® 3.0, side panels (mortalities of 94% in 2018, 66.4% in 2019, and 73.6% in 2020), while full susceptibility was obtained with the roof of PermaNet® 3.0. The F1534C kdr mutation occurred in low frequency, with significant correlation between heterozygote genotypes and DDT resistance. This temporal increase in resistance is a major challenge for control of this vector of public health importance.

Four decades of epidemiological data reveal trajectories towards malaria elimination in Kheda district (Gujarat), western part of India

BackgroundMalaria is a main public health problem in India and was so particularly in the state of Gujarat in the western part of the country. This study assesses the effects...

Partial indoor residual spraying with pirimiphos-methyl as an effective and cost-saving measure for the control of Anopheles gambiae s.l. in northern Ghana

The scale up of indoor residual spraying (IRS) and insecticide treated nets have contributed significantly to global reductions in malaria prevalence over the last two decades. However, widespread pyrethroid resistance has necessitated the use of new and more expensive insecticides for IRS. Partial IRS with pirimiphos-methyl in experimental huts and houses in a village-wide trial was evaluated against Anopheles gambiae s.l. in northern Ghana. Four different scenarios in which either only the top or bottom half of the walls of experimental huts were sprayed, with or without also spraying the ceiling were compared. Mortality of An. gambiae s.l. on partially sprayed walls was compared with the standard procedures in which all walls and ceiling surfaces are sprayed. A small-scale trial was then conducted to assess the effectiveness, feasibility, and cost of spraying only the upper walls and ceiling as compared to full IRS and no spraying in northern Ghana. Human landing catches were conducted to estimate entomological indices and determine the effectiveness of partial IRS. An established transmission dynamics model was parameterized by an analysis of the experimental hut data and used to predict the epidemiological impact and cost effectiveness of partial IRS for malaria control in northern Ghana. In the experimental huts, partial IRS of the top (IRR 0.89, p = 0.13) or bottom (IRR 0.90, p = 0.15) half of walls and the ceiling was not significantly less effective than full IRS in terms of mosquito mortality. In the village trial, the annual entomological inoculation rate was higher for the unsprayed control (217 infective bites/person/year (ib/p/yr)) compared with the fully and partially sprayed sites, with 28 and 38 ib/p/yr, respectively. The transmission model predicts that the efficacy of partial IRS against all-age prevalence of malaria after six months would be broadly equivalent to a full IRS campaign in which 40% reduction is expected relative to no spray campaign. At scale, partial IRS in northern Ghana would have resulted in a 33% cost savings ($496,426) that would enable spraying of 36,000 additional rooms. These findings suggest that partial IRS is an effective, feasible, and cost saving approach to IRS that could be adopted to sustain and expand implementation of this key malaria control intervention.

Evaluation of different deployment strategies for larviciding to control malaria: a simulation study

BackgroundLarviciding against malaria vectors in Africa has been limited compared to indoor residual spraying and insecticide treated nets but is increasingly being considered by some countries as a complementary strategy. However, despite progress towards improved larvicides and new tools for mapping or treating mosquito-breeding sites, little is known about the optimal deployment strategies for larviciding in different transmission and seasonality settings.MethodsA malaria transmission model, OpenMalaria, was used to simulate varying larviciding strategies and their impact on host-seeking mosquito densities, entomological inoculation rate (EIR) and malaria prevalence. Variations in coverage, duration, frequency, and timing of larviciding were simulated for three transmission intensities and four transmission seasonality profiles. Malaria transmission was assumed to follow rainfall with a lag of one month. Theoretical sub-Saharan African settings with Anopheles gambiae as the dominant vector were chosen to explore impact. Relative reduction compared to no larviciding was predicted for each indicator during the simulated larviciding period.ResultsLarviciding immediately reduced the predicted host-seeking mosquito densities and EIRs to a maximum that approached or exceeded the simulated coverage. Reduction in prevalence was delayed by approximately one month. The relative reduction in prevalence was up to four times higher at low than high transmission. Reducing larviciding frequency (i.e., from every 5 to 10 days) resulted in substantial loss in effectiveness (54, 45 and 53% loss of impact for host-seeking mosquito densities, EIR and prevalence, respectively). In seasonal settings the most effective timing of larviciding was during or at the beginning of the rainy season and least impactful during the dry season, assuming larviciding deployment for four months.ConclusionThe results highlight the critical role of deployment strategies on the impact of larviciding. Overall, larviciding would be more effective in settings with low and seasonal transmission, and at the beginning and during the peak densities of the target species populations. For maximum impact, implementers should consider the practical ranges of coverage, duration, frequency, and timing of larviciding in their respective contexts. More operational data and improved calibration would enable models to become a practical tool to support malaria control programmes in developing larviciding strategies that account for the diversity of contexts.

Optimal Control and Cost Effectiveness Analysis of SIRS Malaria Disease Model with Temperature Variability Factor

In this study, we proposed and analyzed the optimal control and cost-effectiveness strategies for malaria epidemics model with impact of temperature variability. Temperature variability strongly determines the transmission of malaria. Firstly, we proved that all solutions of the model are positive and bounded within a certain set with initial conditions. Using the next-generation matrix method, the basic reproductive number at the present malaria-free equilibrium point was computed. The local stability and global stability of the malaria-free equilibrium were depicted applying the Jacobian matrix and Lyapunov function respectively when the basic reproductive number is smaller than one. However, the positive endemic equilibrium occurs when the basic reproductive number is greater than unity. A sensitivity analysis of the parameters was conducted; the model showed forward and backward bifurcation. Secondly, using Pontryagin’s maximum principle, optimal control interventions for malaria disease reduction are described involving three control measures, namely use of insecticide-treated bed nets, treatment of infected humans using anti-malarial drugs, and indoor residual insecticide spraying. An analysis of cost-effectiveness was also conducted. Finally, based on the simulation of different control strategies, the combination of treatment of infected humans and insecticide spraying was proved to be the most efficient and least costly strategy to eradicate the disease.

Understanding challenges to malaria elimination in Nepal: a qualitative study with an embedded capacity-building exercise

BackgroundThe Nepalese Government has made significant progress toward the elimination of malaria. However, given the surge in the prevalence of non-communicable diseases, such as diabetes and hypertension, and the localized nature of malaria prevalence, malaria elimination will remain a challenge. In the current study, the authors sought to understand local perceptions on threats to malaria elimination in three endemic districts.MethodsThe authors conducted a capacity-building exercise embedded within a qualitative study. The study component aimed to understand how local policymakers and actors perceive challenges in malaria elimination. For them to be able to articulate the challenges, however, an understanding of malaria elimination in the context of a broader health system in Nepal would be required. The capacity-building component, thus, involved providing that knowledge.ResultsAlthough the prevalence of malaria is high in the three districts where the study was conducted, there are significant gaps in human resources, diagnosis and treatment, and the provision of indoor residual spraying and long-lasting insecticide treated nets. More importantly, the authors’ experience suggests that it may be possible to capitalize on local expertise in order to identify gaps in malaria elimination at a sub-national level by building in a capacity-building exercise within a study.ConclusionsLocals in three malaria-endemic districts of Nepal perceive that there are significant gaps in human resources, diagnosis and treatment, the provision of insecticide treated nets, and indoor residual spraying.

Risk factors for Burkitt lymphoma in East African children and minors: A case-control study in malaria-endemic regions in Uganda, Tanzania and Kenya.

Endemic Burkitt lymphoma (eBL) is the most common childhood cancer in sub-Saharan African countries, however, few epidemiologic studies have been undertaken and none attempted enrolling cases from multiple countries. We therefore conducted a population-based case-control study of eBL in children aged 0-15 years old in six regions in Northern Uganda, Northern Tanzania and Western Kenya, enrolling 862 suspected cases and 2,934 population controls (response rates 98.5-100%), and processing ~40,000 vials of samples using standardized protocols. Risk factor questionnaires were administered, and malaria period prevalence was measured using rapid diagnostic tests (RDTs). A total of 80.9% of the recruited cases were diagnosed as eBL; 61.4% confirmed by histology. Associations with eBL risk were computed using logistic regression models adjusted for relevant confounders. Associations common in at least two countries were emphasized. eBL risk was decreased with higher maternal income and paternal education and elevated with history of inpatient malaria treatment >12 months before enrollment. Reporting malaria-attributed fever up to 6 months before enrollment and malaria-RDT positivity at enrollment were associated with decreased eBL risk. Conversely, reporting exposure to mass malaria suppression programs (e.g., indoor residual insecticide) was associated with elevated risk. HIV seropositivity was associated with elevated eBL risk, but the relative impact was small. The study shows that it is feasible to conduct networked, multisite population-based studies of eBL in Africa. eBL was inversely associated with socioeconomic status, positively associated with inpatient malaria treatment 12 months ago and with living in areas targeted for malaria suppression, which support a role of malaria in eBL.

The intensity of malaria transmisson and efficacy of Alphacypermethrin as an indoor residual insecticide against malaria vectors in Kadawa, Kano

Malaria is currently affecting more people in the World than any other disease and no single measure of control through the use of drugs seems effective. Malaria is said to kill one African (Whether child or adult every 15 second) and roughly 300,000 Nigerian children annually. A crossectional study was carried out to assess the impact of alphacy phermethrin as an indoor residual insecticide against malaria vectors and transmission in Kadawa irrigation area, Kano. A total of 1897 mosquitoes were collected indoors using WHO standard techniques in the selected areas between December 2010 and June 2011. Specimens were identified using morphological keys and PCR-based assays. ELISA tests were used to detect P. falciparum sporozoite infection. Of the 1897 Anopheles mosquitoes collected, An. funestus group, the predominant vector species, represented 63.6% while An. gambiae s.l. has 18.5% while other anopheles and culicines 17.9%. The control group (Alphacyphermethrin treated group) catch 1332 (85.6%) predominated over the intervention group (Non-alpha cyphernethrin treated group) 224 (14.4%) with an extreme significant difference (P &lt; 0.0001). The result of PCR based test identified 22% of the mosquitoes of the Anopheles gambiae complex collected as An. gambiae s.s., 96% and An. arabiensis as 4%.The overall sporozoite rates for An. funsetus and An. gambiae s.s. were statistically significant in both groups. Infection rates in both intervention and control group were also statistically significant. The result of the study showed that, the indoor residual spray of alphacyphermethrin has seen to have assisted in reduction of malaria transmission and malaria vectors in the study area from 15.9% in control group to 4.1% in intervention group and 78.8% in control group to 21.2% in intervention group respectively. Key words: Malaria; Alpha cyphermethrin; ELISA ; PCR.

A Cross-Sectional Population Study of Geographic, Age-Specific, and Household Risk Factors for Asymptomatic Plasmodium falciparum Malaria Infection in Western Kenya.

The burden of Plasmodium falciparum (Pf) malaria in Kenya is decreasing; however, it is still one of the top 10 causes of morbidity, particularly in regions of western Kenya. Between April 2015 and June 2016, we enrolled 965 apparently healthy children aged 0-15 years in former Nyanza and Western Provinces in Kenya to characterize the demographic, geographic, and household risk factors of asymptomatic malaria as part of an epidemiologic study to investigate the risk factors for endemic Burkitt lymphoma. The children were sampled using a stratified, multistage cluster sampling survey design. Malaria was assessed by rapid diagnostic test (RDT) and thick-film microscopy (TFM). Primary analyses of Pf malaria prevalence (pfPR) are based on RDT. Associations between weighted pfPR and potential risk factors were evaluated using logistic regression, accounting for the survey design. Plasmodium falciparum malaria prevalence was 36.0% (27.5%, 44.5%) by RDT and 22.3% (16.0%, 28.6%) by TFM. Plasmodium falciparum malaria prevalence was positively associated with living in the lake-endemic area (adjusted odds ratio [aOR] 3.46; 95% confidence interval [95% CI] 1.63, 7.37), paternal occupation as peasant farmer (aOR 1.87; 1.08, 3.26) or manual laborer (aOR 1.83; 1.00, 3.37), and keeping dogs (aOR 1.62; 0.98-2.69) or cows (aOR 1.52; 0.96-2.40) inside or near the household. Plasmodium falciparum malaria prevalence was inversely associated with indoor residual insecticide spraying (IRS) (aOR 0.44; 0.19, 1.01), having a household connected to electricity (aOR 0.47; 0.22, 0.98), and a household with two (aOR 0.45; 0.22, 0.93) or ≥ three rooms (aOR 0.41; 0.18, 0.93). We report high but geographically heterogeneous pfPR in children in western Kenya and significant associations with IRS and household-level socioeconomic factors.

Novel Indoor Residual Spray Insecticide With Extended Mortality Effect: A Case of SumiShield 50WG Against Wild Resistant Populations of Anopheles arabiensis in Northern Tanzania.

Resistance of malaria vectors to different classes of insecticides has been reported in malaria-endemic areas. Identifying new indoor residual spray (IRS) compounds that are effective against resistant vector populations is a high priority in managing insecticide resistance. A biological efficacy trial was conducted in the field from August 2016 to February 2017 to determine the efficacy of SumiShield 50WG, a new insecticide class, against wild Anopheles arabiensis. Indoor surfaces of 20 houses in Mabogini ward in the rural district of Moshi in northern Tanzania were sprayed with SumiShield 50WG. Bio-efficacy monitoring was conducted monthly for 6 months after the spray application. In addition, susceptibility tests were conducted by exposing mosquitoes to papers treated with permethrin 0.75%, pirimiphos-methyl 0.25%, and clothianidin 2% (SumiShield 50WG). Representatives from each household included in the study were surveyed about possible side effects or problems faced since the spray. Regression probit analysis was used to calculate knock-down times while the chi-square test was used to compare the mortality effect for mosquitoes. The SumiShield 50WG insecticide maintained optimal efficacy in the field setting for the duration of the 6-month study period, with 100% mortality of mosquitoes by 144 to 168 hours post-exposure to treated surfaces. Susceptibility tests showed some variation in tolerance to the tested insecticide-treated papers, particularly between SumiShield 50WG and pirimiphos-methyl. The knock-down times for 50% and 95% of the mosquitoes when exposed to SumiShield 50WG-treated test paper were 45.81 minutes and 83.85 minutes, respectively, and 67.77 minutes and 105.81 minutes, respectively, for the pirimiphos-methyl-treated papers. There were no short-term adverse side effects reported by households sprayed with SumiShield 50WG. The findings of this study suggest that SumiShield 50WG is a viable IRS insecticide for malaria vector control in Tanzania, especially in areas where pyrethroid resistance is a concern.

Small-scale field evaluation of the efficacy and residual effect of Fludora\xae Fusion (mixture of clothianidin and deltamethrin) against susceptible and resistant Anopheles gambiae populations from Benin, West Africa

BackgroundIn recognition of the threat of insecticide resistance in vectors of malaria, the WHO Global Malaria Programme recommends the development of an appropriate and comprehensive response to insecticide resistance. In principle, good resistance management practice requires the application of multiple insecticides of different modes of action, for example, in rotations and mixtures. Insecticides recommended by the World Health Organization for indoor residual spraying and long-lasting insecticide nets are limited. It is, therefore, judicious to prevent the rapid spread of insecticide resistance by evaluating new insecticides formulations with different modes of action and long residual effect.MethodsFludora® Fusion, a new neonicotinoid IRS formulation (a mixture of 500 g/kg clothianidin and 62.5 g/kg deltamethrin applied 200 mg ai/sqm + 25 mg ai/sqm, respectively) was tested. Small scale field evaluation of this product was conducted in the district of Dangbo in Benin, to compare its efficacy and residual effect on cement and mud walls against those of clothianidin 200 mg ai/sqm (WG 70) alone, and of deltamethrin 25 mg ai/sqm (WG 250) alone. WHO wall cone bioassays were conducted monthly with laboratory susceptible Anopheles “Kisumu” and wild Anopheles gambiae sensu stricto (s.s.) population from Dangbo. The induced mortality by each treatment per wall substrate for 24 h, 48 h, and 72 h post exposure were recorded every month and analysed.ResultsFludora® Fusion and clothianidin WG 70 showed mortality rates over 80% WHO bio-efficacy threshold on cement walls either with susceptible or resistant An. gambiae s.s. over a period of 10 and 9 months, respectively. Treatment with Fludora® Fusion and clothianidin WG 70 on the mud walls showed residual effect for 6 months and 5 months respectively against both susceptible and resistant mosquitoes. During the whole evaluation period, deltamethrin WG 250 showed mortality rates below 80% against resistant Anopheles population. Furthermore, the knock down rates observed with the Fludora® Fusion combination were significantly higher (p < 5%) than those induced by Clothiandin WG 70.ConclusionBoth the Fludora® Fusion combination and clothianidin alone showed very good and lasting efficacy for IRS against resistant Anopheles with some residual benefit provided by the combination. The residual efficacy of the Fludora® Fusion combination evaluated at 10 months shows this product is a good candidate for IRS interventions.

Isolation and characterization of a temperature-sensitive lethal strain of Anopheles arabiensis for SIT-based application

BackgroundMalaria is still a global health problem and vector control is the cornerstone of disease control strategies using indoor residual insecticide spraying (IRS) and insecticide-treated nets. The situation is becoming acute with widespread resistance to the limited arsenal of available insecticide classes. Therefore, new and innovative tools to reduce Plasmodium transmission are in need and this situation raised considerable interest in using sterile insect technique (SIT) against human pest insects, particularly Anopheles malaria vectors. When considering a mosquito release programme, one of the first issues to be addressed is how to eliminate/separate the hematophagous vector females. In this paper, we report the development and evaluation of an Anopheles arabiensis temperature-sensitive lethal (tsl) strain towards its potential use for the development of a genetic sexing strain (GSS).Anopheles arabiensis male mosquitoes originated from North Cameroon were treated with 0.05% ethyl methanesulfonate (EMS). The mutagen was added to 10% sucrose solution and mosquitoes fed ad-libitum for 24h and 48h on a cotton wool soaked with sucrose-mutagen solution placed at the top of the cup. Treated males were then allowed to mate with wild virgin females and their progenies were screened for heat sensitivity from F3 to F8, until the isolation and establishment of a tsl strain which was further characterized by assessing its productivity (fecundity and fertility), larval development, adult longevity as well as nature and inheritance pattern of the tsl.ResultsObservations showed that the number of eggs laid and their hatch rate were similar between females that mated with mutagenized males and those from the control suggesting that mutagenesis didn't affect An. arabiensis male fecundity and fertility. At F3, fourteen isofemale families out of 88 tested, which showed mortalities ranged between 50 and 80 %, were selected as lines potentially containing a tsl mutation. From F4 to F8, a tsl strain was isolated and established by screening L1 larvae at 41°C for 3 hours. This strain showed similar life history traits compared to the wild type strain in terms of fertility, larval development time and adult's emergence. Crossing experiments to further assess the nature and inheritance pattern of the tsl phenotype showed that it is due to a recessive allele located on an autosome.ConclusionThe successful establishment of the An. arabiensis tsl strain is a valuable tool towards the development of a GSS for SIT applications against this species. This will be done by induction of a Y-autosome translocation to link the wild-type allele to the Y chromosome in such manner that males are wild-type (temperature resistant) and females are mutant (temperature sensitive).

Baseline entomologic data on malaria transmission in prelude to an indoor residual spraying intervention in the regions of Alibori and Donga, Northern Benin, West Africa

BackgroundDespite the success of indoor residual insecticide spraying (IRS) in Africa, particularly in Benin, some gaps of information need to be filled to optimize the effectiveness of this intervention in the perspective of the country’s effort to eliminate malaria. In anticipation to the 2018 IRS campaign in two targeted regions of northern Benin, this study aimed, to collect baseline information on vector composition, spatio-temporal variation and peak malaria transmission in the Alibori and Donga, two targeted regions of northern Benin. Information collected will help to better plan the implementation and later on the impact assessment of this IRS campaign.MethodsThe study was carried out in four districts of the two IRS targeted regions of northern Benin. Human landing catches and pyrethrum spray catches protocols were used to assess the biting rate (HBR) and, biting/resting behaviour of malaria vector populations. After morphological identification of collected Anopheles, the heads and thoraxes of Anopheles gambiae sensu lato (s.l.) were analysed by the ELISA CSP tests to estimate the sporozoite index (SI). The entomological inoculation rate was calculated as the product of mosquito biting rate (HBR) and the SI.ResultsThe biting rates of An. gambiae s.l., the major vector in this study sites, varied significantly from region to region. It was higher: in rural than in urban areas, in rainy season than in dry season, indoors than outdoors. Overall, SI was comparable between sites. The highest EIRs were observed in the Donga region (16.84 infectious bites/man/month in Djougou district and 17.64 infectious bites/man/month in Copargo district) and the lowest in the Alibori region (10.74 infectious bites/man/month at Kandi district and 11.04 infectious bites/man/month at Gogounou district).ConclusionThis study showed the heterogeneous and various nature of malaria epidemiology in Northern Benin. Indeed, the epidemiological profile of malaria transmission in the Alibori and Donga regions is made of a single season of transmission interrupted by a dry season. This period of transmission is relatively longer in Donga region than in Alibori. This information can be used to guide the extension of IRS in the Alibori and in the Donga, by primarily targeting areas with short periods of transmission, and easy to cover.

A cross-sectional study of asymptomatic Plasmodium falciparum infection burden and risk factors in general population children in 12 villages in northern Uganda

BackgroundPlasmodium falciparum malaria is an important cause of morbidity in northern Uganda. This study was undertaken to assess village-, household-, and individual-level risk factors of asymptomatic falciparum malaria in children in 12 villages in northern Uganda.MethodsBetween 10/2011 and 02/2014, 1006 apparently healthy children under 16 years old were enrolled in 12 villages using a stratified, multi-stage, cluster survey design and assessed for P. falciparum malaria infection using the rapid diagnostic test (RDT) and thick film microscopy (TFM), and structured interviewer-administered questionnaires. Associations between weighted P. falciparum malaria prevalence (pfPR), based on RDT, and covariates were estimated as odds ratios and 95% confidence intervals (ORs, 95% CIs) using logistic models accounting for the survey design.ResultsAmong 942 (93.5%) children successfully tested, pfPR was 52.4% by RDT and 32.7% by TFM. Overall pfPR was lower in villages where indoor residual insecticide spray (IRS) was, versus not, implemented (18.4% versus 75.2%, P < 0.0001). However, pfPR was heterogeneous both within IRS (10.6–34.8%) and non-IRS villages (63.6–86.2%). Elevated pfPR was associated with having a sibling who was RDT positive (OR 5.39, 95% CI 2.94–9.90, P = 0.0006) and reporting a fever at enrollment (aOR 4.80, 95% CI 1.94–11.9, P = 0.0094). Decreased pfPR was associated with living in an IRS village (adjusted OR 0.06, 95% CI 0.04–0.07, P < 0.0001), in a household with one (aOR 0.48, 95% CI 0.30–0.76) or more than one child below 5 years (aOR 0.23, 95% CI 0.12–0.44, Ptrend = 0.014), and reporting keeping a goat inside or near the house (aOR 0.42, 95% CI 0.29–0.62, P = 0.0021).ConclusionsThe results show high but heterogeneous pfPR in villages in northern Uganda, confirm significantly decreased pfPR associated with IRS implementation, and suggest significant associations with some household characteristics. Further research is needed to elucidate the factors influencing malaria heterogeneity in villages in Uganda.