Effectiveness Of Long-lasting Insecticidal Nets Research Articles

Pyrethroid resistance and gene expression profile of a new resistant An. gambiae colony from Uganda reveals multiple resistance mechanisms and overexpression of Glutathione-S-Transferases linked to survival of PBO-pyrethroid combination

Background The effectiveness of long-lasting insecticidal nets (LLINs) are being threatened by growing resistance to pyrethroids. To restore their efficacy, a synergist, piperonyl butoxide (PBO) which inhibits cytochrome P450s has been incorporated into pyrethroid treated nets. A trial of PBO-LLINs was conducted in Uganda from 2017 and we attempted to characterize mechanisms of resistance that could impact intervention efficacy. Methods We established an Anopheles gambiae s.s colony in 2018 using female mosquitoes collected from Busia district in eastern Uganda. We first assessed the phenotypic resistance profile of this colony using WHO tube and net assays using a deltamethrin dose-response approach. The Busia colony was screened for known resistance markers and RT-qPCR targeting 15 genes previously associated with insecticide resistance was performed. Results The Busia colony had very high resistance to deltamethrin, permethrin and DDT. In addition, the colony had moderate resistance to alpha-cypermethrin and lambda-cyhalothrin but were fully susceptible to bendiocarb and fenitrothion. Exposure to PBO in combination with permethrin and deltamethrin resulted in higher mortality rates in both net and tube assays, with a higher mortality observed in net assays than tube assays. The kdr marker, Vgsc-995S was at very high frequency (91.7-98.9%) whilst the metabolic markers Coeae1d and Cyp4j5-L43F were at very low (1.3% - 11.5%) and moderate (39.5% - 44.7%) frequencies respectively. Our analysis showed that gene expression pattern in mosquitoes exposed to deltamethrin, permethrin or DDT only were similar in comparison to the susceptible strain and there was significant overexpression of cytochrome P450s, glutathione-s-transferases (GSTs) and carboxyl esterases (COEs). However, mosquitoes exposed to both PBO and pyrethroid strikingly and significantly only overexpressed closely related GSTs compared to unexposed mosquitoes while major cytochrome P450s were underexpressed. Conclusions The high levels of pyrethroid resistance observed in Busia appears associated with a wide range of metabolic gene families.

Pyrethroid resistance and gene expression profile of a new resistant An. gambiae colony from Uganda reveals multiple resistance mechanisms and overexpression of Glutathione-S-Transferases linked to survival of PBO-pyrethroid combination

Background: The effectiveness of long-lasting insecticidal nets (LLINs) are being threatened by growing resistance to pyrethroids. To restore their efficacy, a synergist, piperonyl butoxide (PBO) which inhibits cytochrome P450s has been incorporated into pyrethroid treated nets. A trial of PBO-LLINs was conducted in Uganda from 2017 and we attempted to characterize mechanisms of resistance that could impact intervention efficacy. Methods: We established an Anopheles gambiae s.s colony in 2018 using female mosquitoes collected from Busia district in eastern Uganda. We first assessed the phenotypic resistance profile of this colony using WHO tube and net assays using a deltamethrin dose-response approach. The Busia colony was screened for known resistance markers and RT-qPCR targeting 15 genes previously associated with insecticide resistance was performed. Results: The Busia colony had very high resistance to deltamethrin, permethrin and DDT. In addition, the colony had moderate resistance to alpha-cypermethrin and lambda-cyhalothrin but were fully susceptible to bendiocarb and fenitrothion. Exposure to PBO in combination with permethrin and deltamethrin resulted in higher mortality rates in both net and tube assays, with a higher mortality observed in net assays than tube assays. The kdr marker, Vgsc-995S was at very high frequency (91.7-98.9%) whilst the metabolic markers Coeae1d and Cyp4j5-L43F were at very low (1.3% - 11.5%) and moderate (39.5% - 44.7%) frequencies respectively. Our analysis showed that gene expression pattern in mosquitoes exposed to deltamethrin, permethrin or DDT only were similar in comparison to the susceptible strain and there was significant overexpression of cytochrome P450s, glutathione-s-transferases (GSTs) and carboxyl esterases (COEs).  However, mosquitoes exposed to both PBO and pyrethroid strikingly and significantly only overexpressed closely related GSTs compared to unexposed mosquitoes while major cytochrome P450s were underexpressed. Conclusions: The high levels of pyrethroid resistance observed in Busia appears associated with a wide range of metabolic gene families.

THE EFFECT OF LONG-LASTING INSECTICIDAL NETS ON THE DYNAMICS OF MALARIA SPREAD IN INDONESIA

Malaria is an infectious disease that can lead to death. Deaths from malaria globally have increased in 2020. So the spread of this disease is still a serious problem for society. The mathematical model used is the SIR-SI model, assuming that recovered individuals can be re-infected with malaria. Analysis was carried out on the effectiveness parameters of long-lasting insecticidal nets to determine their effect on the dynamics of the spread of malaria. The sensitivity analysis results showed that changes in the parameters of the effectiveness of long-lasting insecticidal nets had an inverse effect on the rate of spread of malaria. These results follow numerical simulations conducted using malaria case data in Indonesia (some assumptions). Thus, efforts can be made to suppress the spread of malaria by increasing the effectiveness of long-lasting insecticidal nets.

Effectiveness of long-lasting insecticidal nets with pyriproxyfen–pyrethroid, chlorfenapyr–pyrethroid, or piperonyl butoxide–pyrethroid versus pyrethroid only against malaria in Tanzania: final-year results of a four-arm, single-blind, cluster-randomised trial

New classes of long-lasting insecticidal nets (LLINs) containing two active ingredients have been recently recommended by WHO in areas where malaria vectors are resistant to pyrethroids. This policy was based on evidence generated by the first 2 years of our recently published trial in Tanzania. In this Article, we report the final third-year trial findings, which are necessary for assessing the long-term effectiveness of new classes of LLIN in the community and the replacement intervals required. A third year of follow-up of a four-arm, single-blind, cluster-randomised controlled trial of dual active ingredient LLINs was conducted between July 14, 2021, and Feb 10, 2022, in Misungwi, Tanzania. Restricted randomisation was used to assign 84 clusters to the four LLIN groups (1:1:1:1) to receive either standard pyrethroid (PY) LLINs (reference), chlorfenapyr-PY LLINs, pyriproxyfen-PY LLINs, or piperonyl butoxide (PBO)-PY LLINs. All households received one LLIN for every two people. Data collection was done in consenting households in the cluster core area with at least one child between 6 months and 15 years of age who permanently resided in the selected household. Exclusion criteria were householders absent during the visit, living in the cluster buffer area, no adult caregiver capable of giving informed consent, or eligible children who were severely ill. Field staff and study participants were masked to allocation, and those analysing data were not. The primary 24-month endpoint was reported previously; here, we present the secondary outcome, malaria infection prevalence in children at 36 months post LLIN distribution, reported in the intention-to-treat analysis. The trial was registered with ClinicalTrials.gov (NCT03554616) and is now complete. Overall usage of study nets was 1023 (22·3%) of 4587 people at 36 months post distribution. In the standard PY LLIN group, malaria infection was prevalent in 407 (37·4%) of 1088 participants, compared with 261 (22·8%) of 1145 in the chlorfenapyr-PY LLIN group (odds ratio 0·57, 95% CI 0·38-0·86; p=0·0069), 338 (32·2%) of 1048 in the PBO-PY LLIN group (0·95, 0·64-1·42; p=0·80), and 302 (28·8%) of 1050 in the pyriproxyfen-PY LLIN group (0·82, 0·55-1·23; p=0·34). None of the participants or caregivers reported side-effects. Despite low coverage, the protective efficacy against malaria offered by chlorfenapyr-PY LLINs was superior to that provided by standard PY LLINs over a 3-year LLIN lifespan. Appropriate LLIN replacement strategies to maintain adequate usage of nets will be necessary to maximise the full potential of these nets. Department for International Development, UK Medical Research Council, Wellcome Trust, Department of Health and Social Care, and Bill & Melinda Gates Foundation via the Innovative Vector Control Consortium.

Evaluation of the protective efficacy of Olyset®Plus ceiling net on reducing malaria prevalence in children in Lake Victoria Basin, Kenya: study protocol for a cluster-randomized controlled trial

BackgroundIn the Lake Victoria Basin of western Kenya, malaria remains highly endemic despite high coverage of interventions such as insecticide-impregnated long-lasting insecticidal nets (LLIN). The malaria-protective effect of LLINs is hampered by insecticide resistance in Anopheles vectors and its repurposing by the community. Ceiling nets and LLIN with synergist piperonyl butoxide (PBO-LLIN) are novel tools that can overcome the problems of behavioral variation of net use and metabolic resistance to insecticide, respectively. The two have been shown to reduce malaria prevalence when used independently. Integration of these two tools (i.e., ceiling nets made with PBO-LLIN or Olyset®Plus ceiling nets) appears promising in further reducing the malaria burden.MethodsA cluster-randomized controlled trial is designed to assess the effect of Olyset®Plus ceiling nets on reducing malaria prevalence in children on Mfangano Island in Homa Bay County, where malaria transmission is moderate. Olyset®Plus ceiling nets will be installed in 1315 residential structures. Malaria parasitological, entomological, and serological indicators will be measured for 12 months to compare the effectiveness of this new intervention against conventional LLIN in the control arm.DiscussionWider adoption of Olyset®Plus ceiling nets to complement existing interventions may benefit other malaria-endemic counties and be incorporated as part of Kenya’s national malaria elimination strategy.Trial registrationUMIN Clinical Trials Registry UMIN000045079. Registered on 4 August 2021.

Anopheles gambiae s.l. larval habitats and resistance mechanisms in Kribi, Cameroon

The effectiveness of Long-Lasting Insecticidal Nets (LLINs) and indoor residual spraying (IRS) in controlling malaria vectors is hampered by the resistance of anopheles to insecticides. A good knowledge of the breeding sites and of the resistance profile of the vectors could facilitate the development of an appropriate control strategy. This study looks at the larval ecology and the susceptibility profile of An. gambiae s.l. to insecticides in urban and rural areas in Kribi, South Region of Cameroon. Mosquito breeding sites were categorized and geo-referenced. For each site, larvae were collected and reared and physicochemical parameters were measured in situ. The susceptibility of anopheles to dichlorodiphenyltrichloroethane (DDT), deltamethrin and permethrin, after pre-exposure to piperonyl butoxide (PBO) or not, was evaluated on the reared larvae. The Kdr mutation was detected using the Hot Oligonucleotide Ligation Assay (HOLA). Natural breeding sites of An. gambiae s.l. were tyre tracks (12%, n=10), unbuilt wells (5%, n=4), pools of residual water (57%, n=48), foot and hoof prints, gullies, streams and the banks of the Kienké River (15%, n=13). Artificial breeding sites were abandoned dugouts (11%, n=9). Breeding sites in urban areas were characterized by higher mean values of temperature, conductivity, salinity and turbidity compared to the breeding sites in the rural area. The breeding sites of An. gambiae s.l. in urban Kribi were found to be sunnier than those in rural Kribi. A total of 4320 adults were used for testing, 1 440 mosquitoes from rural Kribi, 1 440 from urban Kribi and 1 440 specimens from the laboratory Kisumu strain. For DDT and deltamethrin, susceptibility tests showed that mortality was lower in a situation of no pre-exposure to PBO than in a situation of pre-exposure to PBO in the two study areas. The frequency of the resistant allele (R) was high for the Kdr West mutation in both urban (0.94) and rural areas in Kribi (0.93). An. gambiae s.l. colonizes a wide range of breeding sites and develops metabolic and mutation resistance to recommended insecticides. The search of alternative molecules for vector control is a necessity.

Understanding the Intransigence of Malaria in Malawi.

Despite the scale-up of interventions against malaria over the past decade, this disease remains a leading threat to health in Malawi. To evaluate the epidemiology of both Plasmodium falciparum infection and malaria disease, the Malawi International Center of Excellence for Malaria Research (ICEMR) has developed and implemented diverse and robust surveillance and research projects. Descriptive studies in ICEMR Phase 1 increased our understanding of the declining effectiveness of long-lasting insecticidal nets (LLINs), the role of school-age children in malaria parasite transmission, and the complexity of host-parasite interactions leading to disease. These findings informed the design of ICEMR Phase 2 to test hypotheses about LLIN use and effectiveness, vector resistance to insecticides, demographic targets of malaria control, patterns and causes of asymptomatic to life-threatening disease, and the impacts of RTS,S vaccination plus piperonyl butoxide-treated LLINs on infection and disease in young children. These investigations are helping us to understand mosquito-to-human and human-to-mosquito transmission in the context of Malawi's intransigent malaria problem.

Effect of long-lasting insecticidal nets with and without piperonyl butoxide on malaria indicators in Uganda (LLINEUP): final results of a cluster-randomised trial embedded in a national distribution campaign

Long-lasting insecticidal nets (LLINs) are the foundation of malaria control but resistance of mosquito vectors to pyrethroids threatens their effectiveness. We embedded a cluster-randomised trial into Uganda's 2017-18 campaign to distribute LLINs. LLINs with piperonyl butoxide (PBO) reduced parasite prevalence more effectively than conventional LLINs (without PBO) for 18 months. Here, we report the final 25-month survey results. LLINEUP was a cluster-randomised trial conducted in 48 districts in eastern and western Uganda. 104 health subdistricts (clusters) without ongoing or planned indoor residual spraying with pirimiphos-methyl (Actellic, Basel, Switzerland) were eligible for inclusion in the trial. Clusters were randomly assigned to PBO LLINs (PermaNet 3.0 or Olyset Plus) and conventional LLINs (PermaNet 2.0 or Olyset Net) with proportionate randomisation using STATA version 14.2. LLINs were delivered from March 25, 2017, to March 18, 2018. Between April 23, 2019, and Sept 13, 2019, community surveys were conducted in 50 randomly selected households per cluster; ten households per cluster were randomly selected for entomology surveys. Mosquitoes were collected in the morning from indoor surfaces of households using Prokopack aspirators. Due to COVID-19 restrictions, only 90 of the 104 clusters were surveyed at 25 months. The primary outcome was parasite prevalence by microscopy in children aged 2-10 years, assessed in the as-treated population, determined using the results from the 6-month household survey on the type of LLINs received in each cluster. This trial is registered with ISRCTN, ISRCTN17516395, and is now completed. In the as-treated analysis, two clusters were excluded (no predominant LLIN received) and four were reassigned; 40 PBO LLIN clusters (30 PermaNet 3.0, ten Olyset Plus) and 48 non-PBO LLIN (36 PermaNet 2.0, 12 Olyset Net) were included. Parasite prevalence was 17·1% (506 of 2958 participants) in the PBO group and 19·8% (701 of 3534) in the non-PBO group (prevalence ratio adjusted for baseline 0·80 [95% CI 0·69-0·93], p=0·0048). Comparing within-treatment group parasite prevalence to baseline, parasite prevalence ratios were lower in the PBO groups at all timepoints, but the difference was greatest at 6 months (PBO LLINs parasite prevalence at baseline 28·8% [1001 of 3472, 95% CI 27·3-30·4] vs at 6 months 12·0% [361 of 3009, 10·9-13·2], prevalence ratio [PR] 0·43 [95% CI 0·36-0·52], p<0·0001; non-PBO LLINs parasite prevalence at baseline 25·4% [1015 of 4004, 24·0-26·7] vs 6 months 14·8% [526 of 3551, 13·7-16·0], PR 0·60 [0·54-0·68], p<0·0001) and 25 months (PBO LLINs parasite prevalence at 25 months 17·1% [506 of 2958, 15·8-18·5], PR 0·63 [95% CI 0·57-0·71], p<0·0001; non-PBO LLINs parasite prevalence at 25 months 19·8% [701 of 3534, 18·5-21·2], PR 0·79 [0·73-0·86], p<0·0001). In Uganda, PBO LLINs outperformed pyrethroid-only LLINs for 25 months. WHO concluded that PBO LLINs are more effective against malaria than non-PBO LLINs when resistance to pyrethroids is high and issued a conditional recommendation suggesting PBO LLINs should be deployed in areas of pyrethroid resistance. The Against Malaria Foundation, UK Department for International Development, Innovative Vector Control Consortium, and Bill and Melinda Gates Foundation.

Experimental Hut Trials Reveal That CYP6P9a/b P450 Alleles Are Reducing the Efficacy of Pyrethroid-Only Olyset Net against the Malaria Vector Anopheles funestus but PBO-Based Olyset Plus Net Remains Effective.

Malaria remains a major public health concern in Africa. Metabolic resistance in major malaria vectors such as An. funestus is jeopardizing the effectiveness of long-lasting insecticidal nets (LLINs) to control malaria. Here, we used experimental hut trials (EHTs) to investigate the impact of cytochrome P450-based resistance on the efficacy of PBO-based net (Olyset Plus) compared to a permethrin-only net (Olyset), revealing a greater loss of efficacy for the latter. EHT performed with progenies of F5 crossing between the An. funestus pyrethroid-resistant strain FUMOZ and the pyrethroid-susceptible strain FANG revealed that PBO-based nets (Olyset Plus) induced a significantly higher mortality rate (99.1%) than pyrethroid-only nets (Olyset) (56.7%) (p < 0.0001). The blood-feeding rate was higher in Olyset compared to Olyset Plus (11.6% vs. 5.6%; p = 0.013). Genotyping the CYP6P9a/b and the intergenic 6.5 kb structural variant (SV) resistance alleles showed that, for both nets, homozygote-resistant mosquitoes have a greater ability to blood-feed than the susceptible mosquitoes. Homozygote-resistant genotypes significantly survived more with Olyset after cone assays (e.g., CYP6P9a OR = 34.6; p < 0.0001) than homozygote-susceptible mosquitoes. A similar but lower correlation was seen with Olyset Plus (OR = 6.4; p < 0.001). Genotyping EHT samples confirmed that CYP6P9a/b and 6.5 kb_SV homozygote-resistant mosquitoes survive and blood-feed significantly better than homozygote-susceptible mosquitoes when exposed to Olyset. Our findings highlight the negative impact of P450-based resistance on pyrethroid-only nets, further supporting that PBO nets, such as Olyset Plus, are a better solution in areas of P450-mediated resistance to pyrethroids.

LLIN Evaluation in Uganda Project (LLINEUP) – Effect of Long-Lasting Insecticidal Nets with and Without Piperonyl Butoxide on Malaria Indicators in Uganda 25 Months after Distribution: A Cluster-Randomised Trial

LLIN Evaluation in Uganda Project (LLINEUP) – Effect of Long-Lasting Insecticidal Nets with and Without Piperonyl Butoxide on Malaria Indicators in Uganda 25 Months after Distribution: A Cluster-Randomised Trial

The effect of long-lasting insecticidal nets (LLINs) physical integrity on utilization

BackgroundIn Ethiopia, despite improvements in coverage and access, utilization of long-lasting insecticidal nets (LLINs) remains a challenge. Different household-level factors have been identified as associated with LLIN use. However, the contribution of LLIN physical integrity to their utilization is not well investigated and documented. This study aimed to assess the association between the physical integrity of LLINs and their use.MethodsThis study employed a nested case-control design using secondary data from the Ethiopian LLIN durability monitoring study conducted from May 2015 to June 2018. LLINs not used the night before the survey were identified as cases, while those used the previous night were categorized as controls. The physical integrity of LLINs was classified as no holes, good, acceptable, and torn using the proportionate hole index (pHI). A Generalized Estimating Equation (GEE) model was used to assess and quantify the association between LLIN physical integrity and use. The model specifications included binomial probabilistic distribution, logit link, exchangeable correlation matrix structure, and robust standard errors. The factors included in the model were selected first by fitting binary regression, and then by including all factors that showed statistical significance at P-value less than 0.25 and conceptually relevant variables into the multivariate regression model.ResultsA total of 5277 observations fulfilled the inclusion criteria. Out of these 1767 observations were cases while the remaining 3510 were controls. LLINs that were in torn physical condition had higher odds (AOR [95% CI] = 1.76 [1.41, 2.19]) of not being used compared to LLINs with no holes. Other factors that showed significant association included the age of the LLIN, sleeping place type, washing status of LLINs, perceptions towards net care and repair, LLIN to people ratio, economic status, and study site.Conclusion and recommendationLLINs that have some level of physical damage have a relatively higher likelihood of not being used. Community members need to be educated about proper care and prevention of LLIN damage to delay the development of holes as long as possible and use available LLINs regularly.

Effectiveness of long-lasting insecticidal nets in prevention of malaria among individuals visiting health centres in Ziway-Dugda District, Ethiopia: matched case\u2013control study

BackgroundMalaria is a major health problem in Ethiopia. Sleeping under long-lasting insecticidal nets (LLINs) is its major control strategy. Despite high LLINs use (84%) in Ziway-Dugda District, malaria remained a public health problem, raising concern on its effectiveness. Understanding the effectiveness of malaria control interventions is vital. This study evaluated the effectiveness of LLINs and determinants of malaria in Ziway-Dugda District, Arsi Zone Ethiopia.MethodsA matched case–control study was conducted among 284 study participants (71 cases and 213 controls) in Ziway-Dugda District, Arsi Zone, Ethiopia from March to May, 2017. Three health centers were selected randomly, and enrolled individuals newly diagnosed for malaria proportionally. Cases and controls were individuals testing positive and negative for malaria using rapid diagnostic tests. Each case was matched to three controls using the age of (5 years), gender and village of residence. The information was collected using pre-tested structured questionnaires through face to face interviews and observation. Data were entered into Epi-Info version 3.5, and analysed using Stata version-12. Conditional logistic regression was performed, and odds of LLINs use were compared using matched Adjusted Odds Ratio (AOR), 95% confidence interval (CI) and p-value of < 0.05.ResultsOne hundred twenty-three (61.2%) of the controls and 22 (32.8%) of cases had regularly slept under LLINs in the past two weeks. Using multivariate analysis, sleeping under LLINs for the past two weeks (AOR = 0.23, 95%CI = 0.11–0.45); living in houses sprayed with indoor residual spray (IRS) (AOR = 0.23, 95%CI: 0.10–0.52); and staying late outdoors at night in the past two-weeks (AOR = 2.99, 95%CI = 1.44–6.19) were determinant factors.ConclusionsSleeping under LLINs is effective for malaria prevention in the district. IRS and staying late outdoors at night were determinants of malaria. It is recommended to increase attention on strengthening LLINs use and IRS in the area.

Older children are at increased risk of Plasmodium vivax in south-central Ethiopia: a cohort study

BackgroundBetter understanding of the distribution of Plasmodium vivax and its risk factors could be used to prevent and control malaria infection. Therefore, the aim of this study was to characterize the distribution and risk factors of P. vivax, and to compare them with Plasmodium falciparum occurrence in south-central Ethiopia.MethodsA cohort of 34,548 individuals were followed for 121 weeks between 2014 and 2016 as part of larger cluster randomized controlled trial to evaluate the effect of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) on malaria prevention in Ethiopia. Weekly home visit (active search) and patient self- report to health post (passive search) between the weekly home visits were used to register malaria cases. A blood sample was collected by finger prick and malaria was diagnosed using rapid diagnostic test (RDT). Generalized estimating equation (GEE) Poisson model that accounts for repeated measure of malaria episodes was applied to assess the risk factors of P. vivax episode.ResultsThe overall incidence rate of P. vivax was 7.4 episodes per 1000 person-years of observation. The study showed households closer to the lake Zeway and Bulbula river (potential mosquito breeding sites) were more at risk of P. vivax infection (incidence rate ratio (IRR): 1.33; 95% CI = 1.23–1.45). Furthermore, the age group under 5 years (IRR: 1.40, 95% CI = 1.10–1.79), the age group 5–14 years (IRR: 1.27, 95% CI = 1.03–1.57), households with less educated household head (IRR: 1.63, 95% CI = 1.10–2.44) and house roof made of thatch/leaf (IRR: 1.35, 95% CI = 1.11–1.65) were at higher risk for P. vivax. Similar explanatory variables such as distance from the breeding sites, age group (under 5 years but not 5–14 years old), educational status and type of housing were also found to be the predictors of P. falciparum incidence.ConclusionHouseholds living closer to a mosquito breeding site, age group under 15 years, less educated household heads and thatch/leaf roof housing were the risk factor for P. vivax. The result of this study can be used for tailored interventions for malaria control and prevention by prioritizing those living close to potential mosquito breeding site, enhancing bed net use of children less than 15 years of age, and improving housing.

Efficacy of interceptor\xae G2, a long-lasting insecticide mixture net treated with chlorfenapyr and alpha-cypermethrin against Anopheles funestus: experimental hut trials in north-eastern Tanzania

BackgroundThe effectiveness of long-lasting insecticidal nets (LLIN), the primary method for preventing malaria in Africa, is compromised by evolution and spread of pyrethroid resistance. Further gains require new insecticides with novel modes of action. Chlorfenapyr is a pyrrole insecticide that disrupts mitochrondrial function and confers no cross-resistance to neurotoxic insecticides. Interceptor® G2 LN (IG2) is an insecticide-mixture LLIN, which combines wash-resistant formulations of chlorfenapyr and the pyrethroid alpha-cypermethrin. The objective was to determine IG2 efficacy under controlled household-like conditions for personal protection and control of wild, pyrethroid-resistant Anopheles funestus mosquitoes.MethodsExperimental hut trials tested IG2 efficacy against two positive controls—a chlorfenapyr-treated net and a standard alpha-cypermethrin LLIN, Interceptor LN (IG1)—consistent with World Health Organization (WHO) evaluation guidelines. Mosquito mortality, blood-feeding inhibition, personal protection, repellency and insecticide-induced exiting were recorded after zero and 20 washing cycles. The trial was repeated and analysed using multivariate and meta-analysis.ResultsIn the two trials held in NE Tanzania, An. funestus mortality was 2.27 (risk ratio 95% CI 1.13–4.56) times greater with unwashed Interceptor G2 than with unwashed Interceptor LN (p = 0.012). There was no significant loss in mortality with IG2 between 0 and 20 washes (1.04, 95% CI 0.83–1.30, p = 0.73). Comparison with chlorfenapyr treated net indicated that most mortality was induced by the chlorfenapyr component of IG2 (0.96, CI 0.74–1.23), while comparison with Interceptor LN indicated blood-feeding was inhibited by the pyrethroid component of IG2 (IG2: 0.70, CI 0.44–1.11 vs IG1: 0.61, CI 0.39–0.97). Both insecticide components contributed to exiting from the huts but the contributions were heterogeneous between trials (heterogeneity Q = 36, P = 0.02). WHO susceptibility tests with pyrethroid papers recorded 44% survival in An. funestus.ConclusionsThe high mortality recorded by IG2 against pyrethroid-resistant An. funestus provides first field evidence of high efficacy against this primary, anthropophilic, malaria vector.

Operational Evaluation of the Effectiveness of Long-lasting Insecticidal Nets on Human-Vector Contact in an African Urban Malaria Context

BackgroundMalaria is still a major public health concern in Côte d’Ivoire despite mass distribution of long-lasting insecticidal nets (LLINs) as a key preventive strategy. This study intended to evaluate the operational effectiveness of LLINs on the level of human-vector contact using 1 antibody-based biomarker of exposure to Anopheles in urban areas.MethodsThis cross-sectional study collected socio-demographic data and use of LLINs from 9 neighborhoods in the city of Bouaké (Côte d’Ivoire). Dry blood spots performed in children aged >6 months and adults were used to evaluate immunoglobulin G (IgG) responses to the Anopheles gSG6-P1 salivary peptide.ResultsIgG response levels to the salivary peptide were significantly lower in individuals who declared having “always” (n = 270) slept under an LLIN compared with those who had “often” (n = 2087) and “never” (n = 88) slept under an LLIN (P < .0001). IgG response levels to gSG6-P1 between those who declared having “always” and “not always” slept under an LLIN varied according to neighborhood, socio-professional category, and age group.ConclusionsThe human IgG level to this gSG6-P1 salivary peptide could be a useful tool to evaluate the actual effectiveness of LLINs and help design behavioral change interventions that are crucial for sustaining universal coverage.

[Assessing the Effectiveness of Impregnated Mosquito Nets, 36 Months after Their Distribution in the South of Cameroon].

Mosquito control in Cameroon relies largely on the proper use of Long-Lasting Insecticidal Nets (LLINs). It is necessary to monitor their effectiveness in order to propose corrective measures to improve the strategy. The aim of this work was to determine the physical integrity and effectiveness of LLINs (Interceptor brand) on Anopheles gambiae s.l. populations in two urban and rural areas of the Ayos health district. The level of LLIN coverage and use was assessed through a population survey. The physical integrity of LLINs was assessed by measuring the holes according to the WHO method. Bio-efficacy testing of ITNs was carried out according to the cone test protocol using 2-5-day-old, non-blood fed Anopheles gambiae s.l. females from the natural field strain and the reference susceptible strain. Household LLIN coverage rates in urban and rural areas were 55.50% and 66.94%, respectively. On the other hand, the rates of use were 78.01% and 75.22% in urban and rural areas respectively. The proportion of nets that had lost their physical integrity after 36 months of use was 47.00% and 59.63% in urban and rural areas respectively. The size of holes ranged from 0.5 to 25 cm. Alphacypermethrin was found to be ineffective against both strains of Anopheles gambiae s.l. tested. Knockdown rates ranged from 8.5% to 73% for the reference susceptible strain and less than 2.5% for the natural field strain. Mortality rates for the natural strain of Anopheles gambiae s.l. ranged from 0% to 2.5% while they were between 29% and 70% for the susceptible strain. The results show a decrease in the effectiveness of LLINs against the mosquitoes tested. This may be due to the lower than expected WHO possession and use rates of LLINs, their relatively high degree of wear and tear, and the resistance of the vectors to alphacypermethrin.

Assessment of the Durability and Bio-effectiveness of Three Long-Lasting Insecticidal Nets in Three Different Communities After the 2017 Mass Net Distribution Campaign in Benin

Long-lasting insecticidal nets (LLINs) are an essential tool in the fight against malaria. Physical integrity, durability and bio-effectiveness are key variables in the effectiveness of LLINs. The objective of this study was to identify the main factors affecting the survival of three brands of LLINs with different physical characteristics and to assess their bio-effectiveness. A cohort consisting of 1500 LLINs (500 of each) of the brands: DawaPlus®2.0 (polyester, 150 denier, 40 g/m2 fabric weight), PermaNet®2.0 and Yorkool® (polyester, 75 denier, alternating knit pattern with 85 g/m2 fabric weight) was monitored every 6 months in the communes of Ketou, Dogbo and Djougou (from October 2017 to September 2019) based on attrition and integrity measures and median survival in years. We also determined bio-efficacy using the WHO cone test. The physical presence rate was 26.4%, 21.4% and 48.6% respectively for DawaPlus®2.0, PermaNet®2.0 and Yorkool®. The main cause of loss of the three LLINs was displacement, 43.6% (in rural areas) versus 43.2% (in urban areas) with no significant difference (p ˃ 0.05). The median proportional hole index (pHI) ranged from 578 (IQR: 219-843) at 6 months to 196 (IQR: 46-524.5). After 24 months of use, 86.1% were in good condition (0≤pHI&lt;65), 9% were damaged (65≤pHI&lt;643) and 4.2% were too torn (643≤pHI). A significant decrease in physical survival of LLINs (all brands) was observed at 24 months (37.9%, range 34.7-41.3%) compared to 6 months (90.3%, range 88.7-91.8%) (p&lt;0.001). The 24-hour mortality of the three LLINs met WHO requirements for efficacy. The decline in LLIN survival rates during this study highlights the need to develop and implement new strategies to manage this important vector control tool.

Varying levels of protection against Plasmodium falciparium infection were conferred on non-users of long lasting insecticidal nets (LLINS) sleeping in rooms where different number of LLINS were hung in hyper endemic state of West Africa.

The use of Long Lasting Insecticidal Nets (LLINs) has greatly reduced the health and economic impact posed by malaria. This study evaluated the residual effect of LLINs on malaria parasite infections among non-LLIN users sleeping in rooms where nets were hung. This study was carried out at Federal University of Agriculture Abeokuta, Ogun State, Nigeria. A total of 259 students were systematically recruited into this study and were classified into two groups of LLINs users and non-users. The LLIN users were further classified according to the proportion of net usage and this includes; < 50%, exactly 50% and > 50% respectively. Finger prick blood samples were collected from the participants and microscopically analysed for the presence of parasites. Demographic characteristics were also recorded. A general prevalence of 40.5% positivity for malaria was recorded among the study population. A significantly high prevalence (p < 0.05) of malaria was recorded among non-users of LLINs compared to users (AOR 4.66, 95%CI 1.27-17.06). A significantly low prevalence of malaria parasite infection was recorded among non-users of LLINs occupying rooms where LLINs was hung compared with non-users from rooms where LLIN were not used. Furthermore, a reduction in prevalence of malaria and parasite densities was observed among non-users of LLINs (occupying rooms where LLINs was hung) as the proportion of LLIN usage increased in such rooms (p < 0.05). This study showed that some level of protection may be conferred on non-users of LLINs staying in rooms where LLINs are hung.

Effect of long-lasting insecticidal nets with and without piperonyl butoxide on malaria indicators in Uganda (LLINEUP): a pragmatic, cluster-randomised trial embedded in a national LLIN distribution campaign

SummaryBackgroundLong-lasting insecticidal nets (LLINs) are the primary malaria prevention tool, but their effectiveness is threatened by pyrethroid resistance. We embedded a pragmatic cluster-randomised trial into Uganda's national LLIN campaign to compare conventional LLINs with those containing piperonyl butoxide (PBO), a synergist that can partially restore pyrethroid susceptibility in mosquito vectors.Methods104 health sub-districts, from 48 districts in Uganda, were randomly assigned to LLINs with PBO (PermaNet 3.0 and Olyset Plus) and conventional LLINs (PermaNet 2.0 and Olyset Net) by proportionate randomisation using an iterative process. At baseline 6, 12, and 18 months after LLIN distribution, cross-sectional surveys were done in 50 randomly selected households per cluster (5200 per survey); a subset of ten households per cluster (1040 per survey) were randomly selected for entomological surveys. The primary outcome was parasite prevalence by microscopy in children aged 2–10 years, assessed in the as-treated population at 6, 12, and 18 months. This trial is registered with ISRCTN, ISRCTN17516395.FindingsLLINs were delivered to households from March 25, 2017, to March 18, 2018, 32 clusters were randomly assigned to PermaNet 3.0, 20 to Olyset Plus, 37 to PermaNet 2.0, and 15 to Olyset Net. In the as-treated analysis, three clusters were excluded because no dominant LLIN was received, and four clusters were reassigned, resulting in 49 PBO LLIN clusters (31 received PermaNet 3.0 and 18 received Olyset Plus) and 52 non-PBO LLIN clusters (39 received PermaNet 2.0 and 13 received Olyset Net). At 6 months, parasite prevalence was 11% (386/3614) in the PBO group compared with 15% (556/3844) in the non-PBO group (prevalence ratio [PR] adjusted for baseline values 0·74, 95% CI 0·62–0·87; p=0·0003). Parasite prevalence was similar at month 12 (11% vs 13%; PR 0·73, 95% CI 0·63–0·85; p=0·0001) and month 18 (12% vs 14%; PR 0·84, 95% CI 0·72–0·98; p=0·029).InterpretationIn Uganda, where pyrethroid resistance is high, PBO LLINs reduced parasite prevalence more effectively than did conventional LLINs for up to 18 months. This study provides evidence needed to support WHO's final recommendation on use of PBO LLINs.FundingThe Against Malaria Foundation, UK Department for International Development, Innovative Vector Control Consortium, and Bill and Melinda Gates Foundation.

Pyrethroid resistance in sub-Saharan Africa

Long-lasting insecticide nets (LLINs) have had a large role in the reduction of malaria incidence in the endemic countries in sub-Saharan Africa. However, pyrethroid resistance is now widespread and threatens to not only render LLINs irrelevant, but also to reverse the gains made towards malaria elimination. The concern about resistance has prompted a suggestion that insecticides should be removed from LLINs to preserve them for other use in vector control measures. 1 Paaijmans KP Huijben S Taking the ‘I’ out of LLINs: using insecticides in vector control tools other than long-lasting nets to fight malaria. Malar J. 2020; 19: 73 Crossref PubMed Scopus (5) Google Scholar Effect of long-lasting insecticidal nets with and without piperonyl butoxide on malaria indicators in Uganda (LLINEUP): a pragmatic, cluster-randomised trial embedded in a national LLIN distribution campaignIn Uganda, where pyrethroid resistance is high, PBO LLINs reduced parasite prevalence more effectively than did conventional LLINs for up to 18 months. This study provides evidence needed to support WHO's final recommendation on use of PBO LLINs. Full-Text PDF Open Access