Malaria Vector Research Articles

Differential sensitivity and specificity of Aedes aegypti and Anopheles gambiae to adenine nucleotide phagostimulants—an all-or-none response?

BackgroundThe decision to imbibe a blood meal is predominantly dependent on the sensitivity and specificity of haematophagous arthropods to blood-derived adenine nucleotides, in particular adenosine triphosphate (ATP). Despite previous efforts to identify and characterise the specificity and sensitivity to ATP and other adenine nucleotides, as well as the role of other blood-derived phagostimulants across the Culicidae, comparisons across species remain difficult.MethodsThe feeding response of the yellow fever mosquito Aedes aegypti and the African malaria vector Anopheles gambiae to adenine nucleotides in the presence of a carbonate buffer was assessed using a membrane feeding assay. The proportion of mosquitoes engorged and the volume imbibed by all mosquitoes was scored visually and spectrophotometrically. In addition, the proportion of prediuresing An. gambiae, as well as the volume engorged and prediuresed, was examined.ResultsAedes aegypti was more sensitive to adenine nucleotides than An. gambiae, but both species maintained specificity to these phagostimulants, demonstrating a dose-dependent bimodal feeding pattern, thereby expanding our understanding of the all-or-none blood-feeding hypothesis. Feeding on the bicarbonate buffer by An. gambiae—but not that of Ae. aegypti—demonstrated a species-specific variation in how blood phagostimulants are encoded. Adenine nucleotides, with and without bovine serum albumin, were observed to dose-dependently regulate the proportion of An. gambiae prediuresing and the volumes prediuresed but not volumes engorged.ConclusionsTaken together, the results of this study expand our understanding of how mosquitoes differentially assess and respond to blood meal constituents, and provide a basis for further physiological and molecular studies.Graphical

Efficacy of PermaNet® Dual compared to Interceptor® G2 and PermaNet 3.0 in experimental huts in Siaya County, western Kenya

BackgroundPyrethroid-chlorfenapyr nets have shown significant epidemiological impact over pyrethroid-only and pyrethroid plus piperonyl-butoxide (PBO) in Africa. A non-inferiority evaluation of PermaNet® Dual, a new chlorfenapyr plus deltamethrin net, compared to Interceptor® G2, was conducted in experimental huts in Siaya, Kenya against free-flying pyrethroid-resistant Anopheles funestus.MethodsThis study was an experimental hut trial, following a 7 by 7 Latin Square design. Seven treatments and seven sleepers were deployed in the experimental huts daily and rotated weekly and daily, respectively. Mosquitoes were collected every morning between 06:30 h and 08:30 h and were assessed for blood feeding and then monitored for immediate knockdown 1-h post collection and delayed mortality after 72 h. Differences in proportional outcomes were analysed using the blocked logistic regression model, while differences in numerical outcomes were analysed using the negative binomial regression model. Non-inferiority determination was performed based on World Health Organization (WHO) protocol.ResultsMortality at 72 h was 30.2% for PermaNet 3.0, 44.4% for the Interceptor® G2 and 49.2% for the PermaNet® Dual. Blood feeding was highest with PermaNet® Dual at 15%, and least with PermaNet® 3.0 at 10%. PermaNet® Dual and Interceptor® G2 had no significant differences in mortality (OR = 1.10, 95% CI 1.00–1.20) or blood feeding (OR = 1.18, 95% CI 1.04–1.33) and the lower confidence bounds were within the non-inferiority margins but for blood feeding, non-inferiority was relatively high to the upper 95% confidence bound. PermaNet® Dual was non-inferior to the Interceptor® G2 and superior to the PermaNet® 3.0 nets in causing mortality but inferior to PermaNet ®3.0 in blood feeding inhibition of the vectors.ConclusionPermaNet® Dual met the WHO criteria for non-inferiority to Interceptor® G2 and may be considered for deployment for public health use against pyrethroid-resistant Anopheles vectors of malaria.

The effect of next-generation, dual-active-ingredient, long-lasting insecticidal net deployment on insecticide resistance in malaria vectors in Benin: results of a 3-year, three-arm, cluster-randomised, controlled trial

The effect of next-generation, dual-active-ingredient, long-lasting insecticidal net deployment on insecticide resistance in malaria vectors in Benin: results of a 3-year, three-arm, cluster-randomised, controlled trial

Effectiveness of Essential Oils from Leaves of Two Plant Species in the Control of Anopheles gambiae

Background: The current method of controlling malaria vectors using synthetic chemicals has caused serious problems for human health and the environment. Hence, a need for alternative, cheap, readily available, and acceptable mosquito control methods. Objective: To evaluate the bioinsecticidal efficacy of Ocimum gratissimum and Mesosphaerum suaveolens against Anopheles gambiae using the bioassay method. Methods: Oil extracts in 5 ml, 25 ml, and 75 ml serially diluted twice in 100 ml of olive oil formed 0.05%, 0.25%, and 0.75%, while 1 m in 100 ml formed 1%. Olive oil only served as a control. Twenty-five female Anopheles mosquitoes, aged 2-4 days, were blown into tubes containing filter paper-coated essential oils of various concentrations in quadruplicates. Results: Over 50% mortality was recorded in mosquitoes exposed to 0.75% and 1% O. gratissimum compared to others (p <0.05). Knockdown time (KDT) was higher in mosquitoes exposed to 1% O. gratissimum compared to others (p <0.05). Generalized linear regressions showed that the essential oils of O. gratissimum and M. suaveolens contributed 4% (f2 = 0.042) and 14% (f2 = 0.167) to the variability of mortality with time. KDT50 (9.34 - 131.5 minutes) and KDT95 (77.6 - 275 minutes) of O. gratissimum as well as KDT50 (162.8 - 233.6 minutes) and KDT95 (302.8 - 415 minutes) of M. suaveolens were recorded. Stigmastane; 4,22-Stigmastadiene-3-one (Area: 45.88%) in O. gratissimum and gamma-Sitosterol (16.02%) in M. suaveolens were identified by Gas Chromatogram as the highest dose of chemical compounds. Conclusion: The low bioinsecticidal activities of these plant extracts could be attributed to the low occurrence of terpenoids and alkaloids.

Analysis of the 24-h biting patterns and human exposures to malaria vectors in south-eastern Tanzania

BackgroundAfrotropical malaria vectors are generally believed to bite nocturnally, leading to the predominant use of insecticide-treated nets (ITNs), which target indoor, nighttime-biting mosquitoes. This focus is reinforced by biases in entomological surveys, which largely overlook daytime mosquito activity. However, recent evidence challenges this paradigm, showing that Anopheles biting can extend way into the daytime, coinciding with human activities at dawn, daytime and evenings, suggesting a broader risk spectrum and potential protection gaps. We have therefore investigated the diurnal and nocturnal biting patterns of the malaria vectors Anopheles arabiensis and Anopheles funestus in south-eastern Tanzania, to better understand the scope of residual transmission and inform strategies for improved control.MethodsHost-seeking mosquitoes were collected hourly using miniaturized double net traps, both indoors and outdoors over 24-h periods between June 2023 and February 2024. Concurrently, human activities indoors and outdoors were monitored half-hourly to correlate with mosquito collections. A structured questionnaire was used to assess household members’ knowledge, perceptions and experiences regarding exposure to mosquito bites during both nighttime and daytime.ResultsNocturnal biting by An. arabiensis peaked between 7 p.m. and 11 p.m. while that of An. funestus peaked later, between 1 a.m. and 3 a.m. Daytime biting accounted for 15.03% of An. arabiensis catches, with peaks around 7–11 a.m. and after 4 p.m., and for 14.15% of An. funestus catches, peaking around mid-mornings, from 10 a.m. to 12 p.m. Nighttime exposure to An. arabiensis was greater outdoors (54.5%), while daytime exposure was greater indoors (80.4%). For An. funestus, higher exposure was observed indoors, both at nighttime (57.1%) and daytime (69%). Plasmodium falciparum sporozoites were detected in both day-biting and night-biting An. arabiensis. Common daytime activities potentially exposing residents during peak biting hours included household chores, eating, sleeping (including due to sickness), resting in the shade or under verandas and playing (children). From evenings onwards, exposures coincided with resting, socializing before bedtime and playtime (children). Nearly all survey respondents (95.6%) reported experiencing daytime mosquito bites, but only 28% believed malaria was transmissible diurnally.ConclusionsThis study updates our understanding of malaria vector biting patterns in south-eastern Tanzania, revealing considerable additional risk in the mornings, daytime and evenings. Consequently, there may be more gaps in the protection provided by ITNs, which primarily target nocturnal mosquitoes, than previously thought. Complementary strategies are needed to holistically suppress vectors regardless of biting patterns (e.g. using larval source management) and to extend personal protection limits (e.g. using repellents). Additionally, community engagement and education on mosquito activity and protective measures could significantly reduce malaria transmission risk.Graphical

Resistance of Anopheles gambiae s.s. against commonly used insecticides and implication of cytochrome P450 monooxygenase in resistance to pyrethroids in Lambaréné (Gabon)

BackgroundInsecticides are a crucial component of vector control. However, resistance constitute a threat on their efficacy and the gains obtained over the years through malaria vector control. In Gabon, little data on phenotypic insecticide resistance in Anopheles vectors are published, compromising the rational implementation of resistance management strategies. We assessed the susceptibility to pyrethroids, carbamates and organophosphates of Anopheles gambiae sensu lato (s.l.) and discuss the mechanisms involved in the pyrethroid resistance-phenotype.MethodsA. gambiae s.l. larvae were collected from breeding sites in Lambaréné. Emerging adults were used in WHO tube assays at an insecticide concentration that defines resistance (diagnostic concentration). Subsequently, deltamethrin and permethrin were used at 5x and 10x diagnostic concentrations and after preexposure with the cytochrome p450 (and glutathione S-transferase) inhibitor piperonyl butoxide (PBO). A subset of mosquitoes was typed by molecular methods and screened using Taqman assays for mutations conferring target site resistance at the Voltage-gated sodium channel 1014 (Vgsc-1014) locus and the acetylcholinesterase (Ace-1) gene.ResultsAll mosquitoes were A. gambiae sensu stricto (s.s.) and resistant to permethrin, deltamethrin and alphacypermethrin (mortality less than 98%). However, mosquitoes were susceptible to malathion but resistant to bendiocarb. The level of resistance was high for permethrin and at least moderate for deltamethrin. Pre-exposure to PBO significantly increased the mortality of resistant mosquitoes (P < 0.0001). They became fully susceptible to deltamethrin and permethrin-induced mortality increased 4-fold. The G119S Ace-1 resistance allele, which confers resistance to both organophosphates and carbamates, was not present. All sampled mosquitoes were either homozygous for the Vgsc-L1014F or heterozygous for Vgsc-L1014F/L1014S, a marker for resistance to pyrethroids and organochlorides.ConclusionThese findings demonstrate a role of cytochrome P450 monooxygenases in the pyrethroid-resistance of A. gambiae s.s. from Lambaréné. Combining PBO with pyrethroids, as done in second generation bednets, may be used to revert resistance. In addition, malathion could also be used in combination with pyrethroids-based methods for resistance management.

The challenge of improving long-lasting insecticidal nets coverage on Bioko Island: using data to adapt distribution strategies

BackgroundSince 2015, malaria vector control on Bioko Island has relied heavily upon long-lasting insecticidal nets (LLIN) to complement other interventions. Despite significant resources utilised, however, achieving and maintaining high coverage has been elusive. Here, core LLIN indicators were used to assess and redefine distribution strategies.MethodsLLIN indicators were estimated for Bioko Island between 2015 and 2022 using a 1x1 km grid of areas. The way these indicators interacted was used to critically assess coverage targets. Particular attention was paid to spatial heterogeneity and to differences between urban Malabo, the capital, and the rural periphery.ResultsLLIN coverage according to all indicators varied substantially across areas, decreased significantly soon after mass distribution campaigns (MDC) and, with few exceptions, remained consistently below the recommended target. Use was strongly correlated with population access, particularly in Malabo. After a change in strategy in Malabo from MDC to fixed distribution points, use-to-access showed significant improvement, indicating those who obtained their nets from these sources were more likely to keep them and use them. Moreover, their use rates were significantly higher than those of whom sourced their nets elsewhere.ConclusionsStriking a better balance between LLIN distribution efficiency and coverage represents a major challenge as LLIN retention and use rates remain low despite high access resulting from MDC. The cost-benefit of fixed distribution points in Malabo revealed significant advantages, offering a viable alternative for ensuring access to LLINs to those who use them.

Exposure to copper metal enhances the tolerance of An. gambiae s.s. over multiple generations while reducing both fertility and fecundity in this primary malaria vector.

Background Anopheles s.l. displays the potential to develop tolerance to heavy metals, particularly copper, this may occur at a significant biological cost, which can adversely affect its ecological fitness. This study investigated the larval metal exposure on larval development and reproduction of An. gambiae s.s., a laboratory susceptible strain, kisumu. Methods Stage 2 larvae of Anopheles gambiae, Kisumu were exposed to C1 = 484 μg L-1, C2 = 300 μg L-1 and 0 μg L-1 (control) of copper chloride. Larval mortality, pupation time, pupation rate, gonotrophic cycle length, fecundity and fertility of larvae/adults were assessed over six generations. Results Results revealed that larval mortality rate was significantly higher in the C1 groups of each group (p = 0.000), but this mortality rate decreased over generations. Pupation time was extended to 13 and 14 days respectively for C2 and C1 groups (p = 0.000) compared to the control group. Similar results were observed for the gonotrophic cycle, which increased from 4 days at G0 to more than 6 days at generation 5 in adults of C1. The pupation rate in generation 4 (C1) and generation 5 of the same group (p = 0.000) as well as the emergence rate in generation 4 (C2, p = 0.000) and generation 5 (C1 and C2, p = 0.000) decreased significantly compared to the control group. The average number of eggs laid was lower in the test groups from generation 4 to generation 5 (C1 and C2, p = 0.00) and egg fertility was also negatively affected by exposure of the larval stage of An. gambiae s.s. to copper. Conclusion Although studies have already shown that copper induces resistance in An. gambiae s.l. to insecticides, this study has shown that this adaptation requires a non-negligible biological cost in the life of the insect.

Eco-friendly synthesis of silver nanoparticles using Phyllanthus niruri leaf extract: Assessment of antimicrobial activity, effectiveness on tropical neglected mosquito vector control, and biocompatibility using a fibroblast cell line model

Abstract Mosquitoes are rapidly advancing as vectors of several severe diseases. The increasing resistance of mosquitoes and the environmental harm caused by insecticides pose significant challenges for eradicating mosquito vectors. In this study, 18 plant extracts were tested for larvicidal properties against Aedes aegypti, Culex quinquefasciatus, and Anopheles stephensi larvae. Phyllanthus niruri (Pn) showed enhanced larvicidal activity in both laboratory and field trials. The biosynthesis of silver nanoparticles (AgNPs) using Pn leaf methanol extract (Pn-LME) was confirmed by UV-visible spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy. Among various concentrations, 3 mM AgNPs exhibited significant LC90 values of 0.83, 1.46, and 9.11 ppm compared to 9.25, 93.48, and 14.60 ppm of Pn-LME against A. stephensi, C. quinquefasciatus, and A. aegypti, respectively. This indicates the high mortality of mosquito vectors at low AgNP concentrations. Additionally, Pn-AgNPs showed enhanced antibacterial activity and no cytotoxicity in normal fibroblast cells (L929). Field trials demonstrated a 98.70% decrease in mosquito larval density at A. stephensi breeding sites, a 96.55% reduction at C. quinquefasciatus sites, and a 97.85% reduction at Ae. aegypti sites. This study presents an eco-friendly and cost-effective AgNP bio-pesticide synthesized from Pn leaves for controlling and preventing the transmission of filarial, dengue, and malaria vectors.

A novel broad-spectrum antibacterial and anti-malarial Anopheles gambiae Cecropin promotes microbial clearance during pupation.

Anophelinae mosquitoes are exposed to a variety of microbes including Plasmodium parasites that cause malaria. When infected, mosquitoes mount versatile immune responses, including the production of antimicrobial peptides. Cecropins are one of the most widely distributed families of antimicrobial peptides in insects and all previously studied Anopheles members are playing roles in adult mosquito immunity. We have identified and characterized a novel member of the Anopheles gambiae cecropin family, cecropin D (CecD), that is uniquely expressed and immune-responsive at late larval stages to promote microbial clearance through its broad-spectrum antibacterial activity during larval-pupal developmental transition. Interestingly, Cecropin D also exhibited highly potent activity against Plasmodium falciparum sporozoites, the malaria parasite stage that is transmitted from mosquitoes and infects humans and thereby holds promise as a malaria transmission-blocking agent. Finally, we have defined unequivocal cecropin-specific molecular signatures to systematically organize the diversity of the cecropin family in malaria vectors.

The efficacy of attractive targeted sugar baits in reducing malaria vector abundance in low-endemicity settings of northwest Mali

BackgroundAttractive targeted sugar baits (ATSBs) have the potential to significantly reduce infective female Anopheles mosquitoes in arid areas, such as in Northern Mali. Malaria is epidemic in the north due to the limited viability of Anopheles species in the desert climate.The goal of this study was to determine of the effect of ATSB on the number of older female An. gambiae and on the number of sporozoite-positive females in villages in northern Mali.MethodsVillages were located in the north of Mali. In this study, 5677 ATSB stations were deployed, two on each home, in ten villages during late July and early August 2019. Ten villages served as controls. After a pre-treatment monitoring period in July, An. gambiae populations were monitored again from August to December using CDC-UV light traps, pyrethrum spray catches (PSC), and human landing catches (HLC). Mosquitoes were dissected to estimate their age, while ELISA detected sporozoite positivity. The monthly entomological inoculation rates (EIRs) were calculated for HLC indoors and outdoors. Data from villages were compared using t-tests, while bait station weighted density versus amount of collected females was checked with a Pearson’s correlation.ResultsA total of 2703 female An. gambiae were caught from treated villages, 4582 from control villages, a 41.0% difference. Dissection of 1759 females showed that ATSB significantly reduced the number of older females. The proportion of older females in treated villages was 0.93% compared to 9.4% in control villages. ELISA analysis of 7285 females showed that bait stations reduced the number of sporozoite-positive females. The infective females in treated villages was 0.30% compared to 2.73% in the controls. The greater the density of bait stations deployed, the fewer the older, infective females (P < 0.05).EIRs were low in control villages except in months when An. gambiae populations were high. EIRs in ATSB placement villages remained zero. Significant reductions (P < 0.0001) in An. gambiae males were observed.ConclusionsBait stations reduced all measures of vector populations in this study. In a low-transmission setting, ATSB has the potential to greatly reduce malaria.

Landscape and meteorological determinants of malaria vectors' presence and abundance in the rural health district of Korhogo, Côte d'Ivoire, 2016-2018, and comparison with the less anthropized area of Diébougou, Burkina Faso.

Understanding how weather and landscape shape the fine-scale distribution and diversity of malaria vectors is crucial for efficient and locally tailored vector control. This study examines the meteorological and landscape determinants of (i) the spatiotemporal distribution (presence and abundance) of the major malaria vectors in the rural region of Korhogo (northern Côte d'Ivoire) and (ii) the differences in vector probability of presence, abundance, and diversity observed between that area and another rural West African region located 300 km away in Diébougou, Burkina Faso. We monitored Anopheles human-biting activity in 28 villages of the Korhogo health district for 18 months (2016 to 2018), and extracted fine-scale environmental variables (meteorological and landscape) from high-resolution satellite imagery. We used a state-of-the-art statistical modeling framework to associate these data and identify environmental determinants of the presence and abundance of malaria vectors in the area. We then compared the results of this analysis with those of a similar, previously published study conducted in the Diébougou area. The spatiotemporal distribution of malaria vectors in the Korhogo area was highly heterogeneous and appeared to be strongly determined and constrained by meteorological conditions. Rice paddies, temporary sites filled by rainfall, rivers and riparian forests appeared to be the larval habitats of Anopheles mosquitoes. As in Diébougou, meteorological conditions (temperatures, rainfall) appeared to significantly affect all developmental stages of the mosquitoes. Additionally, ligneous savannas were associated with lower abundance of malaria vectors. Anopheles species diversity was lower in Korhogo compared to Diébougou, while biting rates were much higher. Our results suggest that these differences may be due to the more anthropized nature of the Korhogo region in comparison to Diébougou (less forested areas, more agricultural land), supporting the hypothesis of higher malaria vector densities and lower mosquito diversity in more anthropized landscapes in rural West Africa. This study offers valuable insights into the landscape and meteorological determinants of the spatiotemporal distribution of malaria vectors in the Korhogo region and, more broadly, in rural west-Africa. The results emphasize the adverse effects of the ongoing landscape anthropization process in the sub-region, including deforestation and agricultural development, on malaria vector control.

Host Preferences and Impact of Climate on Blood Feeding in Anopheles funestus Group from South Africa.

Anopheles vaneedeni and Anopheles parensis (members of the An. funestus group) are generally not considered malaria vectors. However, both species were recently identified as potential vectors in South Africa. A critical factor needed to determine their role in malaria transmission is their preference for human blood. The human blood index of An. vaneedeni and An. parensis and their potential role in the ongoing residual malaria transmission in South Africa is unknown. This study aimed to identify host blood meals from the wild-caught An. funestus group in a longitudinal study, and to establish the relationship between temperature, relative humidity, and precipitation on host feeding preferences. Anopheles leesoni, An. parensis, An. vaneedeni, and Anopheles rivulorum were collected, and females mainly fed on cattle. Climatic parameters did not influence the host feeding preferences of these four members of the An. funestus group, but impacted the proportion of females that took a blood meal. Significant changes in feeding proportions were driven by relative humidity, temperature, and precipitation. The role of these species in the ongoing residual malaria transmission in South Africa needs further investigation, as no human blood meals were identified. It is recommended that vector surveillance teams incorporate climatic monitoring and host blood meal identification into their routine activities. This information could provide the malaria vector control programmes with scientific evidence to evaluate the importance of the An. funestus group in residual malaria transmission.

A quantitative and systematic analysis of Anopheles stephensi bionomics and control approaches

Anopheles stephensi is a mosquito endemic to South Asia and the Arabian Peninsula that has recently been detected in eight African countries, posing a significant threat to global malaria control efforts. A challenge with An. stephensi is that it requires unique surveillance and control tools when compared to other malaria vectors. Through a systematic literature review, we investigated the efficacy of trapping methods and controls for An. stephensi mosquitoes, with a focus on studies of its behavior and biology. Data from 83 articles (native range: Afghanistan, India, Iran, Iraq, Pakistan, and Qatar; invasive range: Djibouti, Ethiopia, Sri Lanka, Saudi Arabia, and Sudan) met our study inclusion criteria. Data from these studies revealed that using host-seeking animal baited traps increased the number of mosquitoes collected per trap per day in the native range when compared to host-seeking human baited traps. However, these differences were not present in data collection rate assessments from the invasive range. We also found that An. stephensi equally used a large variety of breeding habitats in the native range, but that it tended to prefer water reservoirs and wastewater in the invasive range. Finally, we found that temephos, fenthion, Bacillus thuringiensis israelensis, and Beauveri bassiana were more effective at reducing larvae in their native range compared to the approaches found in our systematic literature search, but the relative effectiveness of these approaches in the invasive range was less clear. Understanding proven historical surveillance and control approaches is essential to the advancement of invasive An. stephensi mitigation efforts, but continued investigations in the invasive range are critical to reducing the impacts of malaria morbidity and mortality.

The potential of gene drives in malaria vector species to control malaria in African environments

Gene drives are a promising means of malaria control with the potential to cause sustained reductions in transmission. In real environments, however, their impacts will depend on local ecological and epidemiological factors. We develop a data-driven model to investigate the impacts of gene drives that causes vector population suppression. We simulate gene drive releases in sixteen ~ 12,000 km2 areas of west Africa that span variation in vector ecology and malaria prevalence, and estimate reductions in vector abundance, malaria prevalence and clinical cases. Average reductions in vector abundance ranged from 71.6–98.4% across areas, while impacts on malaria depended strongly on which vector species were targeted. When other new interventions including RTS,S vaccination and pyrethroid-PBO bednets were in place, at least 60% more clinical cases were averted when gene drives were added, demonstrating the benefits of integrated interventions. Our results show that different strategies for gene drive implementation may be required across different African settings.

A study on the effectiveness of (+)-usnic acid as oral toxic sugar bait against adult male and female Anopheles gambiae

BackgroundDespite the application of various tools for the control of vectors of Plasmodium falciparum, malaria remains the major killer disease in sub-Saharan Africa accounting for up to 90% of deaths due to the disease. Due to limitations of the useage of chemical insecticides such as resistance, negative impact on the environment and to nontarget organisms, the World Health Organization (WHO) requires that affected countries find alternative vector control tools. This study evaluated the effectiveness of ( +)-usnic acid (UA) as an insecticide through oral administration to male and female Anopheles gambiae as an alternative or additional active ingredient to be used in toxic sugar bait.Methods( +)-usnic acid was diluted using acetone at 5, 10, and 15 mg/ml concentrations in three replicates. A 5 ml mixture of 2% food dye and 10% sugar using chlorine-free water mixed with the dilutions of the ( +)-usnic acid and negative control was made containing 2% food dye and 10% sugar solution. The preparations were soaked on a ball of cotton wool and placed over the net of a cup. 5 male and 5 non-blood-fed female newly hatched starved An. gambiae Kisumu strain were introduced together into a cup and monitored for knockdown and mortalities after 4, 24 48, and 72 h. The data were analysed using a multiple linear regression model using the lm function, a base R function and a posthoc test were conducted on the significant main effects and interaction terms using the emmeans function from the emmeans R package. All analyses were performed in RStudio using base R (version 4.3.3).ResultsThere was high mortality of both male and female An. gambiae after ingestion of the toxic sugar bait. 15 mg/ml usnic acid caused the highest mortality (50%) within the first 4 h compared to 5 and 10 mg/ml ( +)-UA. There was a decline in the mortality rate with increased exposure time from 24 to 72 h, however, there was a significant difference in mortality at 5, 10 and 15 mg/ml. Acute toxicity was associated with ingestion of 15 mg/ml after 24 h. 72 h post-mortality was lower in all concentrations than in the control. High mortality was observed among females over the first 4 h (60%) compared to males (40%) due to higher feeding rate of the toxic agent. The proportion of dead males and females was equal after 24 h while after 48 h, the proportion of dead males was high.There was a significantly lower mortality rate after 72 h for both males and females (0 to 13.3%). Compared to all the treatments, high mortality of males was observed.ConclusionsThe results of this study indicate that ( +)-UA when administered as oral sugar bait to An. gambiae has insecticidal properties and is a suitable ingredient to be used as a toxic agent in the novel attractive toxic sugar bait for the control of malaria vectors. ( +)-UA may be an alternative active ingredient as toxic bait in the effort to reduce and eliminate the transmission of Plasmodium falciparum in Africa.

The non-inferiority of piperonyl-butoxide Yorkool® G3 insecticide-treated nets compared to Olyset®Plus measured by Anopheles arabiensis mortality in experimental huts in Tanzania

BackgroundNon-inferiority trials are recommended by the World Health Organization (WHO) to demonstrate that health products show comparable efficacy to that of existing standard of care. As part of the WHO Global Malaria Programme (GMP) process of assessment of malaria vector control products, a second-in-class insecticide-treated net (ITN) must be shown to be non-inferior to a first-in-class product based on mosquito mortality. The public health impact of the first-in-class pyrethroid-piperonyl butoxide (PBO) ITN, Olyset® Plus, has been demonstrated in epidemiological trials in areas with insecticide-resistant mosquitoes, but there is a need to determine the efficacy of other pyrethroid-PBO nets to ensure timely market availability of nets in order to increase access to ITNs. The non-inferiority of a deltamethrin-PBO ITN Yorkool® G3 was evaluated entomologically against Olyset® Plus in experimental huts in Tanzania, following WHO guidelines for non-inferiority trials.MethodsThe trial of the two pyrethroid-PBO ITNs was conducted in experimental huts in Lupiro, Tanzania, using a randomized 7 × 7 Latin square block design. The study ran for 49 nights in 14 huts assessing the mosquito mortality and blood-feeding of wild, free-flying, pyrethroid-resistant Anopheles arabiensis. Using the non-inferiority approach, the comparative efficacy (primary endpoint was mosquito mortality at 24 h and secondary endpoint was blood-feeding) of unwashed and 20 times field-washed pyrethroid-PBO Yorkool® G3 ITNs, were compared with the first-in-class product Olyset® Plus and against a pyrethroid-only ITN, PermaNet® 2.0 ITNs, as a standard comparator.ResultsThe experimental hut trial demonstrated non-inferiority and superiority of Yorkool® G3 to Olyset® Plus based on mosquito mortality [51% vs. 39%, OR 1.68 (95% CI 1.50–1.88)], given that lower 95% CI exceeded 0.74 (delta of 39%) and the margin of no difference (1). Blood-feeding inhibition was high for all treated ITNs (> 90%) and Yorkool® G3 was non-inferior to Olyset® Plus [4% vs. 2%, OR 1.81 (95% CI 1.46–2.39)], given that upper 95% CI was less than 4.85 (delta of 4%). The pyrethroid-PBO ITNs were superior to the pyrethroid-only net, PermaNet® 2.0, as determined by both the proportion of mortality and blood-feeding of mosquitoes (p-value < 0.05).ConclusionYorkool® G3 ITNs demonstrated non-inferiority to the first-in-class Olyset® Plus and superiority over the standard pyrethroid-only ITN, PermaNet® 2.0 as measured by mortality and blood-feeding inhibition of wild pyrethroid-resistant An. arabiensis mosquitoes. Yorkool® G3 ITNs are potential tools for the control of metabolic insecticide-resistant malaria vectors, and their market availability will contribute to the cost-effective selection of ITNs by malaria control programmes to improve population access to ITNs.

Экология техносферы человеческого сообщества

In the 19th century, the sphere of interest of the science of “ecology” was formulated. Over the course of a century and a half, the semantics of its tasks has undergone significant changes. However, the original definition of ecology given by E.G. Haeckel, as a science about the interaction of living and inanimate nature, has again become relevant with the technological development of mankind. This development led to the emergence of an alternative habitat - the technosphere. The technosphere, within the framework of environmental ideas, is considered as a formation deeply hostile to nature in its essence. Nature is considered as a certain ideal that creates favorable conditions for the existence of living organisms in it. The experience of natural disasters and cataclysms, accompanied by the mass death of living organisms, indicates that this is an idealized idea. The existence of modern man outside the technosphere is practically impossible. The techno-sphere takes on the task of providing humanity with protection from pathogens. An example of such control is the use of DDT against vectors of malaria and other diseases. The technosphere solves problems in relation to humanity that are similar to providing the body with food, solving the problems of energy supply and movement over various distances – both people and cargo. The technosphere is evolving, using the achievements of developing sciences and technologies, reducing the specific impact on the natural environment while meeting the needs of the individual. For the further development of human ecology at the intersection of natural and artificial, the solution of traditional management problems is required: strict control of raw materials, technologies and products used, and their rational distribution. This is important since the human population is steadily growing and a significant part of the planet’s population finds itself in conditions of food and energy shortages, while the other part has an abundance of resources.

Why does malaria transmission continue at high levels despite universal vector control? Quantifying persistent malaria transmission by Anopheles funestus in Western Province, Zambia

BackgroundSome settings continue to experience a high malaria burden despite scale-up of malaria vector control to high levels of coverage. Characterisation of persistent malaria transmission in the presence of standard control measures, also termed residual malaria transmission, to understand where and when individuals are exposed to vector biting is critical to inform refinement of prevention and control strategies.MethodsSecondary analysis was performed using data collected during a phase III cluster randomized trial of attractive targeted sugar bait stations in Western Province, Zambia. Two seasonal cohorts of children aged 1–14 years were recruited and monitored monthly during the malaria transmission season, concurrent with entomological surveillance using a combination of human landing catch (HLC) and Centres for Disease Control (CDC) light traps at randomly selected households in study clusters. Behavioural data from cohort participants were combined with measured Anopheles funestus landing rates and sporozoite positivity to estimate the human behaviour-adjusted entomological inoculation rate (EIR).ResultsBehavioural data from 1237 children over 5456 child-visits in 20 entomology surveillance clusters were linked with hourly landing rates from 8131 female An. funestus trapped by HLC. Among all An. funestus tested by enzyme-linked immunosorbent assay (ELISA), 3.3% were sporozoite-positive. Mean EIR directly measured from HLC was 0.07 infectious bites per person per night (ib/p/n). When accounting for child locations over the evening and night, the mean behaviour-adjusted EIR was 0.02 ib/p/n. Children not sleeping under insecticide-treated nets (ITNs) experienced 13.6 infectious bites per person per 6 month season, 8% of which occurred outdoors, while ITN users received 1.3 infectious bites per person per 6 month season, 86% of which were received outdoors. Sleeping under an ITN can prevent approximately 90% of potential An. funestus bites among children.ConclusionsIn this setting ITNs have a high personal protective efficacy owing to peak An. funestus biting occurring indoors while most individuals are asleep. However, despite high household possession of ITNs (>90%) and high individual use (>70%), children in this setting experience more than one infectious bite per person per 6 month transmission season, sufficient to maintain high malaria transmission and burden. New tools and strategies are required to reduce the malaria burden in such settings.Graphical

Expression and Purification of the Full Length and N-Terminal Truncated Variants of Insect CYP6Z2 in the Cytosol of Escherichia Coli for Potential 3D Experimental Studies

Cytochrome P450 enzymes (P450s) offer innate resistance defence for malaria vectors against the insecticides permitted by WHO to be used in vector control tools. P450s can detoxify broad substrates and simultaneously metabolise them, thus the availability of experimental three-dimensional structures of these key insecticide detoxifiers is vital to improving our knowledge of their enzyme activities. Despite the importance of this family of proteins in insecticide resistance, there are no available experimental three-dimensional structures of insect P450 yet. For this investigation, a carboxy-terminal Histidine-tagged recombinant CYP6Z2 was heterologously expressed in E. coli to generate a soluble holoprotein suitable for an experimental three-dimensional structure. The expressed enzyme was purified from the cytosol of E. coli via the combination of various purification techniques and cholic acid sodium salt. Two truncated N-terminal signal peptides: short deletion of 11 amino acids and long deletion of 23 amino acids of the hydrophobic domain, were created to prevent aggregation, improve solubility, and facilitate crystallisation. The CYP6Z2 (full length) produced a holoprotein with a P450 protein concentration of 0.60 nmol/mL, whereas the two truncated CYP6Z2 isoforms produced only the inactive species with no peak at 450 nm. We conclude that the hydrophobic signal peptide region of the insect Cytochrome P450s seems sensitive and indispensable to ensuring 3-D folding and stability.