Vector Populations Research Articles

RNA interference protocols for gene silencing in the spittlebug Philaenus spumarius, vector of Xylella fastidiosa

RNA interference (RNAi) is double stranded RNA (dsRNA)-based gene silencing mechanism. Exogenous dsRNAs application to crops has raised as a powerful tool to control agricultural pests. In particular, several sap-feeder are important plant pathogens vectors, such as Philaenus spumarius, known as main vector of Xylella fastidiosa (Xf), causal agent of olive quick decline syndrome (OQDS) in southern Italy. Here, dsATP synthase beta (dsATP), dsLaccase (dsLacc) and dsGreen Fluorescent Protein (dsGFP) as control, were provided to spittlebug adults by microinjection or to nymphs fed on dsRNA-treated plant shoots. Treated insects were collected at different time points to monitor silencing efficiency over time, describing significant reduction of transcript levels from 8 to 24 days post treatment. Downregulation of target genes ranged from 2- to 16-fold compared to the corresponding dsGFP controls, where highest silencing effects were generally noticed for ATP synthase beta. Sequencing of libraries obtained from total smallRNA (sRNA) showed the generation of dsRNA-derived sRNAs by RNAi pathway, with majority of reads mapping exclusively on the correspondent dsRNA. Also, we characterized components of a functional RNAi machinery in P. spumarius. Further research is needed to clarify such mechanism, screen effective target lethal genes to reduce vector population and improve delivery strategies.

5.C. Scientific session: Strengthen resilience against emerging vector-borne diseases through the ECDC Fellowship Programmes

Abstract Over the past decade, climate change has impacted the transmission of a wide range of vector-borne diseases (VBDs) in Europe, where locally transmitted outbreaks have occurred. It has been implicated in the observed expansion of competent disease vectors in Europe such as Aedes albopictus, which transmits diseases such as Zika, Dengue and Chikungunya. Climate may influence the life cycle of vectors, and the reproduction rate of viral particles inside vectors and human hosts, which means that upsurges in temperature can reduce the incubation period of these pathogens and the life cycle of vectors, thus boosting transmission risk through elevated vector populations. Moreover, globalization and international air travel contribute to pathogen and vector dispersion internationally. Risk mapping suggests further expansion of the species in northern Europe due to climate change. The above underscores the necessity for more proactive measures, such as developing an effective vector control program by monitoring the density and distribution of hosts and pathogens at urban, national, and cross-border levels. Additionally, establishing early warning systems based on integrated human and zoonotic and entomological surveillance is crucial to detect alerts promptly and comprehend where and when infections may emerge or spread. Furthermore, cross-border collaboration and harmonization of vector-borne surveillance systems across European countries may improve preparedness, control and response to mosquito-borne diseases. Preparedness and response require significant efforts from EU Member States and neighbouring countries. Only through a multidisciplinary approach, involving multiple sectors, can we truly prepare to address public health threats. To contribute to strengthening resilience against cross-border public health and emerging health threats in EU Member States and neighbouring countries, the European Centre of Disease Prevention and Control (ECDC) has established three fellowship training programmes. These programmes aim to create and maintain a network of highly qualified epidemiologists, microbiologists and public health professionals and strengthen the public health epidemiology workforce at EU and neighbor countries. This workshop will offer attendees a comprehensive overview of the ECDC’s fellowship programmes, describe how they function and explain their role in preparing for health threats. It will provide examples of three projects carried out by fellows on the implementation of preparedness, response and control measures for emerging vector-borne diseases in European countries at local, national and multinational levels. Those will set the scene for an in-depth analysis of the key challenges faced and can help promote awareness that integrated, multidisciplinary interventions are both feasible and effective in reducing the threat of vector-borne infectious diseases spreading in Europe and neighboring countries. Key messages • ECDC fellowship programmes aim to strengthen resilience against emerging public health threats in EU Member States and neighboring countries. • Fellows are engaged in national and cross-border integrated and multidisciplinary interventions to strengthen preparedness and mitigate the spread of emerging vector-borne diseases.

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.

Analysis of the interrelationship between precipitation and confirmed dengue cases in the city of Recife (Brazil) covering climate and public health information

Large-scale epidemics of arboviruses, such as dengue, have heightened societal awareness regarding the necessity of combating the primary transmission vectors. Equally critical is the identification of environmental conditions and variables that influence vector population dynamics. Aedes aegypti, the primary vector of arboviruses such as dengue and Zika in Brazil, is closely associated with the climatic and geographical conditions of urban environments. This study examines the relationship between precipitation and confirmed dengue cases in Recife (Brazil), employing regression and quantile analyses to evaluate the influence of meteorological conditions on the disease’s spread. The findings reveal a direct correlation between monthly averages of precipitation and confirmed cases, although this is apparent only when excluding years of epidemic peaks. The highest number of cases generally aligns with the rainy season, and the lowest with the dry season, with weak, moderate and strong precipitation events being closely linked to increased dengue incidence. However, notable discrepancies were identified: four out of six major outbreaks occurred in drier months, challenging the assumption of a straightforward relationship between rainfall and dengue incidence. These findings underscore the multifaceted nature of dengue dynamics, suggesting that while precipitation plays a significant role, other factors, including serotype circulation and broader climatic phenomena, are equally critical in driving outbreaks. This complexity highlights the need for a more comprehensive understanding of the mechanisms influencing dengue epidemics.

Gene Sequencing Study of Mitochondrial Cytochrome Oxidase Subunit I (COI) in Aedes aegypti Mosquito

Aedes aegypti is an important vector from the public health point of view. It transmits pathogens of Dengue and various other diseases. Controlling vector populations is key to reducing disease transmission and it is possible by understanding the taxonomic characteristics of the vectors and their genetic analysis helps in the identification of the genetic variations in species of different geographical areas. The main aim of the present study is the screening of the Aedes mosquito genome of local species as genetic studies give some insights into the vaccine for the treatment of the diseases caused by mosquito species. In the present study, the adult Ae. aegypti collected from Suryapet town where Dengue fever is endemic, used for the mitochondrial Cytochrome Oxidase subunit I (COI) gene sequencing using the techniques of polymerase chain reaction, Electrophoretic separation, spectrophotometric analysis, and BLAST. The mitochondrial COI sequence of 583 bps is published in the National Centre for Biotechnology Information (NCBI) with accession number ON413769. The sequence data was matched with the database available in the NCBI to identify variation in the gene as this gene keeps changing in the organisms and may contribute to the species establishing itself in a particular region due to congenial environmental conditions. One match with the protein called haem copper oxidase subunit I. The transmission of different pathogens in different areas can be ascertained by comparing similar sequence studies documented. Genomic studies involving genetic markers are of immense help in developing the vaccine. The mitochondrial COI gene is the marker often used for evolutionary research. The single nucleotide polymorphisms (SNP) or Restricted fragment length polymorphisms (RFLPs) that occur in DNA also contribute to the vector's adaptability to the different geographical areas and also the survival benefit which are the basis for understanding the vectors thoroughly and their role in disease transmission.

Dengue-mediated changes in the vectorial capacity of Aedes aegypti (Diptera: Culicidae): manipulation of transmission or infection by-product?

An arthropod's vectorial capacity summarizes its disease transmission potential. Life-history traits, such as fecundity or survival, and behavioral traits, such as locomotor activity, host-seeking and feeding behavior, are important components of vectorial capacity. Studies have shown that mosquito-borne pathogens may alter important vectorial capacity traits of their mosquito vectors, thus directly impacting their transmission and epidemic potential. Here, we compile and discuss the evidence supporting dengue-mediated changes in the yellow fever mosquito Aedes aegypti (L.), its primary vector, and evaluate whether the observed effects represent an evolved trait manipulation with epidemiological implications. Dengue infection appears to manipulate essential traits that facilitate vector-host contact, such as locomotor activity, host-seeking, and feeding behavior, but the underlying mechanisms are still not understood. Conversely, life-history traits relevant to vector population dynamics, such as survival, oviposition, and fecundity, appear to be negatively impacted by dengue virus. Overall, any detrimental effects on life-history traits may be a negligible cost derived from the virulence that dengue has evolved to facilitate its transmission by manipulating Ae. aegypti behavior and feeding performance. However, methodological disparities among studies render comparisons difficult and limit the ability to reach well-supported conclusions. This highlights the need for more standardized methods for the research into changes in virus-mediated traits. Eventually, we argue that the effects on life-history traits and behavior outlined here must be considered when assessing the epidemiological impact of dengue or other arbovirus-vector-host interactions.

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.

Sugar feeding in triatomines: a new perspective for controlling the transmission of Chagas disease.

Introduction: Triatomines are vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. Currently, there is no vaccine against this disease. Thus, control of the insect vector population is the main strategy available to reduce the number of cases. Triatomines are considered obligate hematophagous, but different alternative feeding behaviors were described, such as haemolymphagy or plant feeding. Methods: To determine the preference for sugar feeding in nymphs and adults of Rhodnius prolixus, the insects were exposed a piece of cotton containing bromophenol blue plus sucrose. In addition, we offered several sugars for different species of triatomines, and tested sugar meals as a route of delivery of insecticides in first-instar nymphs of R. prolixus. The effect of sugar feeding on the physiology of these different species of triatomines was recorded. Results: First instar nymphs ingested sucrose more strongly than other stages, and showed high mortality rates. In different species of triatomines, sucrose induced an ingestion, but engorgement varied according to the species. R. prolixus nymphs showed an indiscriminate intake of various sugars, with very different physiological effects. Furthermore, ingesting different combinations of insecticides + sugar significantly reduced insect survival. Discussion: In summary, we described for the first-time sugar feeding as a widespread behavior in several species of triatomines, and the possibility of the use of toxic sugar baits for the control of these vectors. The knowledge of feeding behavior in these insects can be fundamental for the development of new strategies to control Chagas disease.

Genotype distribution and allele frequency of thioester-containing protein 1(Tep1) and its effect on development of Plasmodium oocyst in populations of Anopheles arabiensis in Ethiopia.

Thioester-containing protein 1 (TEP1) is a crucial component of mosquitoes' natural resistance to parasites. To effectively combat malaria, there is a need to better understand how TEP1 polymorphism affects phenotypic traits during infections. Therefore, the purpose of this study was to determine the Tep1 genotype frequency in malaria vector populations from south-western Ethiopia and investigate its effect on Plasmodium oocyst development in Anopheles arabiensis populations. Using standard dippers, Anopheles mosquito larvae were collected from aquatic habitats in Asendabo, Arjo Dedessa, and Gambella in 2019 and 2020. Collected larvae were reared to adults and identified morphologically. Female An. gambiae s.l. were allowed to feed on infected blood containing the same number of gametocytes obtained from P. falciparum and P. vivax gametocyte-positive individuals using indirect membrane feeding methods. Polymerase Chain Reaction (PCR) was used to identify An. gambiae s.l. sibling species. Three hundred thirty An. gambiae s.l. were genotyped using Restricted Fragment Length Polymorphism (RFLP) PCR and sub samples were sequenced to validate the TEP1 genotyping. Among the 330 samples genotyped, two TEP1 alleles, TEP1*S1 (82% frequency) and TEP1*R1 (18% frequency), were identified. Three equivalent genotypes, TEP1*S1/S1, TEP1*R1/R1, and TEP1*S1/R1, had mean frequencies of 65.15%, 2.12%, and 32.73%, respectively. The nucleotide diversity was ranging from 0.36554 to 0. 46751 while haplotype diversity ranged from 0.48871 to 0.63161, across all loci. All sample sites had positive Tajima's D and Fu's Fs values. There was a significant difference in the TEP1 allele frequency and genotype frequency among mosquito populations (p < 0.05), except populations of Anopheles arabiensis from Asendabo and Gambella (p > 0.05). In addition, mosquitoes with the TEP1 *RR genotype were susceptible and produced fewer Plasmodium oocysts than mosquitoes with the TEP1 *SR and TEP1 *SS genotypes. The alleles identified in populations of An. arabiensis were TEP1*R1 and TEP1*S1. There was no significant variation in TEP1*R1 allele frequency between the high and low transmission areas. Furthermore, An. arabiensis carrying the TEP1*R1 allele was susceptible to Plasmodium infection. Further studies on vector-parasite interactions, particularly on the TEP1 gene, are required for vector control techniques.

Evaluating the impact of biogenic nanoparticles and pesticide application in controlling cotton leaf curl virus disease (CLCuD) in cotton (Gossypium hirsutum L.)

BackgroundCotton leaf curl virus disease (CLCuD) is one of the major concerns for cotton growers. The traditional approach to managing CLCuD involves the control of the vector (whitefly) population through the use of pesticides. This study compares the efficacy of zinc oxide, iron oxide, copper and silver nanoparticles with conventional pesticides. Nanoparticles dose was optimized by evaluating their phytotoxic threshold in our previous study. In this study, optimized doses of nanoparticles such as zinc oxide (100 ppm), iron oxide (50 ppm), copper (50 ppm) and silver nanoparticles (25 ppm) were applied in a field trial of cotton against cotton leaf curl virus disease (CLCuD). Morphological parameters (height of stem, monopodial branches, sympodial branches, staple length, boll weight and number of bolls), yield parameters (seed cotton yield and ginning outturn), chlorophyll content (chlorophyll a, chlorophyll b, carotenoids and total chlorophyll), biochemical parameters (superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), hydrogen peroxide (H2O2) and electrolyte leakage) and disease parameters (reduction infection, disease severity and disease incidence) were determined in this study.ResultsThe incidence of cotton leaf curl virus was confirmed by triple antibody sandwich–enzyme-linked immunosorbent assay (TAS-ELISA). The pesticide Imidacloprid significantly reduced the infection by 79.3%. However, in comparison to pesticide, application of nanoparticles also reduced the infection. ZnO NPs reduced the infection by 42.33%, FeO NPs by 41%, Cu NPs by 34.7%, and Ag NPs by 44.8%. Moreover, these nanoparticles also improved the plant growth parameters as compared to control treatment. ZnO NPs enhanced morphological, yield parameters, and chlorophyll content by 36%, 22%, and 29%, respectively. FeO NPs showed improvements by 38%, 21%, and 29%; Cu NPs 39%, 25%, and 29%; and Ag NPs 31%, 19%, and 18%, respectively.ConclusionAlthough treatment pesticide showed the least disease incidence compared to nanoparticles, nanoparticles are eco-friendly and safe as compared to pesticides. Farmers can apply these nanoparticles at their optimal thresholds through foliar application as an alternative to traditional pesticides. It is concluded that nanocomposites and hybrid modes may be used for managing CLCuD efficiently in the future.Graphical abstract

A century of medical records reveal earlier onset of the malaria season in Haut-Katanga induced by climate change

BackgroundDespite worldwide efforts to eradicate malaria over the past century, the disease remains a significant challenge in the Democratic Republic of the Congo (DRC) today. Climate change is even anticipated...

Changes in seasonality and sex ratio of scrub typhus: a case study of South Korea from 2003 to 2019 based on wavelet transform analysis

BackgroundScrub typhus (ST, also known as tsutsugamushi disease) is a common febrile vector-borne disease in South Korea and commonly known as autumn- and female-dominant disease. Although understanding changes in seasonality and sex differences in ST is essential for preparing health interventions, previous studies have not dealt with variations in periodicity and demographic characteristics in detail. Therefore, we aimed to quantify the temporal dynamics of seasonal patterns and sex differences in the incidence of ST in South Korea.MethodsWe extracted epidemiological week (epi-week)-based ST cases from 2003 to 2019 Korean National Health Insurance Service data (ICD-10-CM code: A75.3). To determine changes in seasonality and sex differences, year-, sex-, and age-group-stratified male-to-female ratios and wavelet transform analyses were conducted.ResultsBetween 2003 and 2019, 213,976 ST cases were identified. The incidence per 100,000 population increased by 408.8% from 9.1 in 2003 to 37.2 in 2012, and subsequently decreased by 59.7% from 2012 to 15.0 in 2019. According to the continuous wavelet transform results, ST exhibited a dual seasonal pattern with dominant seasonality in autumn and smaller seasonality in spring from 2005 to 2019. Overall, the periodicity of seasonality decreased, whereas its strength decreased in autumn and increased in spring. With an overall male-to-female ratio being 0.68:1, the ratio has increased from 0.67:1 in 2003 to 0.78:1 in 2019 (Kendall’s τ = 0.706, p < 0.001). However, interestingly, the ratio varied significantly across different age groups.ConclusionsOur findings quantitatively demonstrated changes in seasonality with dual seasonal pattern and shortened overall periodicity and a decrease in sex differences of ST in South Korea. Our study suggests the need for continuous surveillance on populations of vector and host to address ST dynamics to preemptively prepare against global warming.

Space-time dynamics of the dengue epidemic in Brazil, 2024: an insight for decision making

BackgroundDengue is a vector-borne viral infection caused by the dengue virus transmitted to humans primarily by Aedes aegypti. The year 2024 has been a historic year for dengue in Brazil, with the highest number of probable cases ever registered. Herein, we analyze the temporal trend and spatio-temporal dynamics of dengue cases in Brazil during the first nine epidemiological weeks (EW) of 2024.MethodsThis is an ecological study, including all probable cases of dengue in Brazil during the period, carried out in two steps: time series analysis to assess the temporal trend and spatial analysis to identify high-risk clusters.Results1,345,801 probable cases of dengue were reported. The regions with the highest increasing trend were the Northeast with an average epidemiologic week percent change (AEPC) of 52.4 (95% CI: 45.5–59.7; p < 0.001) and the South with 35.9 (95% CI: 27.7–44.5; p < 0.001). There was a statistically significant increasing trend in all states, except Acre (AEPC = -4.1; 95% CI: -16.3–10; p = 0.55), Amapá (AEPC = 1.3; 95% CI: -16.2–22.3; p = 0.9) and Espírito Santo (AEPC = 8.9; 95% CI: -15.7–40.6; p = 0.5). The retrospective space-time analysis showed a cluster within the Northeast, Central-West and Southeast regions, with a radius of 515.3 km, in which 1,267 municipalities and 525,324 of the cases were concentrated (RR = 6.3; p < 0.001). Regarding the spatial variation of the temporal trend, 21 risk areas were found, all of them located in Southeast or Central-West states. The area with the highest relative risk was Minas Gerais state, where 5,748 cases were concentrated (RR = 8.1; p < 0.001). Finally, a purely spatial analysis revealed 25 clusters, the one with the highest relative risk being composed of two municipalities in Acre (RR = 6.9; p < 0.001).ConclusionsWe described a detailed temporal-spatial analysis of dengue cases in the first EWs of 2024 in Brazil, which were mainly concentrated in the Southeast and Central-West regions. Overall, it is recommended that governments adopt public policies to control the the vector population in high-risk areas, as well as to prevent the spread of dengue fever to other areas of Brazil.

Seroprevalence of dengue, yellow fever, and related flaviviruses among the rural human population in Nguruman and Kerio Valley, Kenya

BackgroundYellow fever virus (YFV) and dengue virus (DENV) are among the major re-emerging arboviruses that pose a significant threat to public health. Their associated burden and prevalence can be substantially underestimated due to insufficient surveillance and inadequate diagnosis. This study aimed to determine evidence of dengue, yellow and related flaviviruses circulation among the rural human populations residing in Nguruman (Kajiado County) and Kerio Valley (Baringo County), two dryland ecosystems in the Kenyan Rift Valley.MethodsSerum samples obtained from febrile patients between 5 and 85 years through a hospital-based cross-sectional survey from July 2020 – May 2023, were screened for neutralizing antibodies to YFV, DENV-2 and related flaviviruses, West Nile virus (WNV) and Zika virus (ZIKV) via Plaque reduction neutralization test (PRNT). The study sites and important demographic characteristics were obtained using a structural questionnaire and the data analyzed and seroprevalence compared. A multinomial logistic regression model was done to predict risk for each of the most prevalent viruses with covariates; age, gender, and occupation.ResultsOverall, 54.5% (50.1–59.0% 95% confidence interval (CI) of the samples tested positive for at least one of the four Flaviviruses. The percentage was significantly higher in Kerio Valley (64.34%, 184/286) than in Nguruman (40.2%, 78/194) (P&amp;lt;0.0001). YFV had the highest prevalence, followed by WNV (16.25%), ZIKV (5.2%), and DENV-2 (1%). Kerio Valley had a significantly higher YFV seroprevalence (51%) than Nguruman (6%) (P&amp;lt;0.0001), while DENV-2 was observed only in Nguruman with a low seropositivity of 2%. In contrast to Nguruman, where seropositivity rates were higher in males at 47.47% (P=0.049), in Kerio Valley, females showed considerably higher viral seropositivity at 60.82% than males (P&amp;lt;0001).ConclusionThe study suggests that there is significant circulation of Flaviviruses in both regions, posing a public health risk, that could potentially contribute to clinical disease. However, seropositivity rates vary for each specific site. Furthermore, there could be a risk of YFV, WNV, and ZIKV transmission in both sites with DENV transmission specifically noted in Nguruman. The study findings inform direct cost-effective actions (such as YF vaccines) and precise surveillance data of vector populations for improved disease risk prediction.

Variation in spatial population structure in the Anopheles gambiae species complex.

Anopheles gambiae, Anopheles coluzzii, and Anopheles arabiensis are three of the most widespread vectors of malaria parasites, with geographical ranges stretching across wide swaths of Africa. Understanding the population structure of these closely related species, including the extent to which populations are connected by gene flow, is essential for understanding how vector control implemented in one location might indirectly affect vector populations in other locations. Here, we assessed the population structure of each species based on a combined data set of publicly available and newly processed whole-genome sequences. The data set included single nucleotide polymorphisms from whole genomes of 2,410 individual mosquitoes sampled from 128 locations across 19 African countries. We found that A. gambiae sampled from several countries in West and Central Africa showed low genetic differentiation from each other according to principal components analysis (PCA) and ADMIXTURE modeling. Using Estimated Effective Migration Surfaces (EEMS), we showed that this low genetic differentiation indicates high effective migration rates for A. gambiae across this region. Outside of this region, we found eight groups of sampling locations from Central, East, and Southern Africa for which A. gambiae showed higher genetic differentiation, and lower effective migration rates, between each other and the West/Central Africa group. These results indicate that the barriers to and corridors for migration between populations of A. gambiae differ across the geographical range of this malaria vector species. Using the same methods, we found higher genetic differentiation and lower migration rates between populations of A. coluzzii in West and Central Africa than for A. gambiae in the same region. In contrast, we found lower genetic differentiation and higher migration rates between populations of A. arabiensis in Tanzania, compared to A. gambiae in the same region. These differences between A. gambiae, A. coluzzii, and A. arabiensis indicate that migration barriers and corridors may vary, even between very closely related species. Overall, our results demonstrate that migration rates vary both within and between species of Anopheles mosquitoes, presumably based on species-specific responses to the ecological or environmental conditions that may impede or facilitate migration, and the geographical patterns of these conditions across the landscape. Together with previous findings, this study provides robust evidence that migration rates between populations of malaria vectors depend on the ecological context, which should be considered when planning surveillance of vector populations, monitoring for insecticide resistance, and evaluating interventions.

Cryptic population structure and insecticide resistance in Anopheles gambiae from the southern Democratic Republic of Congo

The Democratic Republic of Congo (DRC) suffers from one of the highest malaria burdens worldwide, but information on its Anopheles vector populations is relatively limited. Preventative malaria control in DRC is reliant on pyrethroid-treated nets, raising concerns over the potential impacts of insecticide resistance. We sampled Anopheles gambiae from three geographically distinct populations (Kimpese, Kapolowe and Mikalayi) in southern DRC, collecting from three sub-sites per population and characterising mosquito collections from each for resistance to pyrethroids using WHO tube bioassays. Resistance to each of three different pyrethroids was generally high in An. gambiae with < 92% mortality in all tests, but varied between collections, with mosquitoes from Kimpese being the most resistant. Whole genome sequencing of 165 An. gambiae revealed evidence for genetic differentiation between Kimpese and Kapolowe/Mikalayi, but not between the latter two sample sites despite separation of approximately 800 km. Surprisingly, there was evidence of population structure at a small spatial scale between collection subsites in Kimpese, despite separation of just tens of kilometres. Intra-population (H12) and inter-population (FST) genome scans identified multiple peaks corresponding to genes associated with insecticide resistance such as the voltage gated sodium channel (Vgsc) target site on chromosome 2L, a Cyp6 cytochrome P450 cluster on chromosome arm 2R, and the Cyp9k1 P450 gene on chromosome X. In addition, in the Kimpese subsites, the P450 redox partner gene Cpr showed evidence for contemporary selection (H12) and population differentiation (FST) meriting further exploration as a potential resistance associated marker.

Whole-genome sequencing of major malaria vectors reveals the evolution of new insecticide resistance variants in a longitudinal study in Burkina Faso

BackgroundIntensive deployment of insecticide based malaria vector control tools resulted in the rapid evolution of phenotypes resistant to these chemicals. Understanding this process at the genomic level is important for the deployment of successful vector control interventions. Therefore, longitudinal sampling followed by whole genome sequencing (WGS) is necessary to understand how these evolutionary processes evolve over time. This study investigated the change in genetic structure and the evolution of the insecticide resistance variants in natural populations of Anopheles gambiae over time and space from 2012 to 2017 in Burkina Faso.MethodsNew genomic data have been generated from An. gambiae mosquitoes collected from three villages in the western part of Burkina Faso between 2012 and 2017. The samples were whole-genome sequenced and the data used in the An. gambiae 1000 genomes (Ag1000G) project as part of the Vector Observatory. Genomic data were analysed using the analysis pipeline previously designed by the Ag1000G project.ResultsThe results showed similar and consistent nucleotide diversity and negative Tajima’s D between An. gambiae sensu stricto (s.s.) and Anopheles coluzzii. Principal component analysis (PCA) and the fixation index (FST) showed a clear genetic structure in the An. gambiae sensu lato (s.l.) species. Genome-wide FST and H12 scans identified genomic regions under divergent selection that may have implications in the adaptation to ecological changes. Novel voltage-gated sodium channel pyrethroid resistance target-site alleles (V402L, I1527T) were identified at increasing frequencies alongside the established alleles (Vgsc-L995F, Vgsc-L995S and N1570Y) within the An. gambiae s.l. populations. Organophosphate metabolic resistance markers were also identified, at increasing frequencies, within the An. gambiae s.s. populations from 2012 to 2017, including the SNP Ace1-G280S and its associated duplication. Variants simultaneously identified in the same vector populations raise concerns about the long-term efficacy of new generation bed nets and the recently organophosphate pirimiphos-methyl indoor residual spraying in Burkina Faso.ConclusionThese findings highlighted the benefit of genomic surveillance of malaria vectors for the detection of new insecticide resistance variants, the monitoring of the existing resistance variants, and also to get insights into the evolutionary processes driving insecticide resistance.

Flupyradifurone application: A promising approach to curtail tomato leaf curl New Delhi virus (ToLCNDV) transmission vectored by Bemisia tabaci in potato farming

The whitefly, Bemisia tabaci, serves as a carrier and transmitter of the tomato leaf curl New Delhi virus (ToLCNDV) in potatoes, leading to the emergence of potato apical leaf curl disease. Among the six insecticides tested against B. tabaci, flupyradifurone resulted in the highest mortality of nymphs and adults. Three effective insecticides were then further evaluated for their ability to prevent the acquisition and transmission of ToLCNDV by B. tabaci. Utilizing qPCR techniques, we determined the amount of virus acquired by B. tabaci from virus-positive plants that had undergone prior insecticide treatment. The results revealed a significant reduction in virus levels in the whitefly's body, flupyradifurone was found to be most effective among the tested insecticides in reducing ToLCNDV acquisition. Flupyradifurone also exhibited the highest efficacy in reducing ToLCNDV transmission by B. tabaci. Experiments conducted in the glasshouse 24 h post insecticide application demonstrated the complete prevention of ToLCNDV transmission in all plants treated with flupyradifurone. In the field experiment also, flupyradifurone effectively suppressed whitefly-mediated ToLCNDV transmission for up to 14 days following insecticide application. The findings indicate that the use of flupyradifurone has the potential to manage the vector population and control associated viral disease, which is known to cause significant losses in potato crops.

Innovation in vector control of dengue hemorrhagic fever using portable devices mechanical electric methods

This innovation was created to control the dengue hemorrhagic fever (DHF) vector population in the larval cycle because several previous control methods were considered less sensitive, effective, and efficient. To test the effectiveness of portable electrical-mechanical methods in controlling Aedes aegypti larvae. The research design was posttest only which was tested on 80-liter and 90-liter volume containers in light and dark colors. Statistical analysis used the independent samples t-test, and Pearson correlation (α=5%). Laboratory test results show that the average time needed to suck all the larvae in a light-colored container with a volume of 80 liters is 38 seconds (28-57 seconds) and a volume of 90 liters is 99.6 seconds (80-119 seconds). In a dark-colored container, the 80-liter volume is 50.8 seconds (3-89 seconds) and the 90-liter volume is 106.8 seconds (88-122 seconds). This tool sucks larvae faster in containers with a volume of 80 liters compared to a volume of 90 liters. The greater the volume of water and the higher the water surface, the longer it takes to suck the larvae. This tool is effective and efficient in speeding up the process of monitoring, collecting, and controlling larvae in large containers.

The bioefficacy of a novel VECTRON™ T500 indoor residual spray formulation in an experimental huts trial against Anopheles gambiae s.l. populations

Background: The emergence of insecticide resistance and its spread through populations of malaria vectors has decreased the number of insecticides available for control. Insecticide resistance has been observed in vector populations across sub-Saharan Africa in malaria endemic areas. Therefore, new compounds with different modes of action are needed that can be used in the management of resistance. The current study assessed the bioefficacy of the new indoor residual spray formulation, VECTRON™ T500 against Klypson 500 WG and water against laboratory reared and wild populations of Anopheles gambiae s.l.. The comparative experimental hut trial was implemented between June 2022 and December 2022 to determine the efficacy of VECTRON™ T500, containing the active ingredient (ai) broflanilide as a 50 % wettable powder (WP). The efficacy of VECTRON™ T500 was compared with a positive control, Klypson 500 WG, a wettable granule (WG) formulation that contains 50 % clothianidin. Cement and mud walls were sprayed with VECTRON™ T500, Klypson 500 WG with water sprayed as a negative control. The two insecticides and negative control were evaluated monthly for six months against laboratory and the field-derived An. gambiae s.l. using the standard WHO cone bioassays. Each wall had two cones on each day of testing. VECTRON™ T500 was sprayed on both surface types at a rate of 100mg ai/m2 whilst Klypson 500 WG was applied at a rate of 300 mg ai/m2. For both wall surface types, the vector from the laboratory-reared and the wild populations exhibited a low knockdown effect to both VECTRON™ T500 and Klypson 500 WG. A total of 3,840 mosquitoes were used of which 2,880 (75 %) were susceptible colony of An. gambiae s.s. and 960 (25 %) were wild An. gambiae s.l.. The VECTRON™ T500 induced a mortality of 97.8 %-98.1 % in the laboratory population and 83.2-95.0 % wild population mosquitoes on cement and mud-walled huts respectively while Klypson 500 WG ranged from 89.6-99.0 % for wild and 99.0-99.3 % for the laboratory population mosquitoes on cement and mud walls respectively. The knockdown due to VECTRON™ T500 was 7.08 % in the sixth month, while for Klypson 500 WG was 16.04-17.50 %. The monthly wall cone bioassay mortality with VECTRON™ T500 remained over 80 % for 6 months post-spraying for both laboratory and wild populations. The findings of this study have shown VECTRON™ T500 to have extended efficacy against malaria vector mosquitoes when applied to cement and mud walls. The evaluated new IRS formulation, VECTRON™ T500, performed equally with the positive control, Klypson 500 WG, regarding its impact on vector mortality.