A cocktail polymerase chain reaction assay to identify members of the Anopheles funestus (Diptera: Culicidae) group

Phenotypic and genotypic insecticide resistance profiles of main malaria vectors in Kwale county, coastal Kenya

BACKGROUND

Long-lasting insecticidal nets are the primary malaria vector control measure in coastal Kenya. In 2018, phenotypic resistance to pyrethroids and low frequency of L1014S kdr mutation were reported in the Anopheles gambiae complex. Since then, additional pyrethroid-treated nets were distributed in 2021. The objectives of this study were to determine the insecticide resistance profiles of An. gambiae and Anopheles funestus from Kwale County and evaluate potential resistance mechanisms.

METHODS

From July 2023 to May 2024, adult and larval collections of An. funestus and An. gambiae mosquitoes were done with the aim of conducting insecticide susceptibility bioassays using WHO protocol for permethrin, deltamethrin, bendiocarb, DDT and pirimiphos-methyl. Species found resistant to pyrethroids were subjected to synergism testing by pre-exposure to piperonyl-butoxide (PBO). This was followed by genotyping of resistance-associated mutations in An. funestus (CYP6P9a, CYP6P9b, GSTe2-L119F and 6.5kb S.V) and An. gambiae (kdr L1014S and L1014F). Sibling species identification was done using PCR. The association between genetic markers and phenotypic resistance was explored using logistic regression.

RESULTS

A total of 1826 An. gambiae and 715 An. funestus were used in insecticide susceptibility bioassays. Both An. gambiae and An. funestus were resistant to permethrin (mortality, 58.7% and 57.1, respectively) and deltamethrin (mortality 51% and 76%, respectively), but susceptible to DDT, bendiocarb and Pirimiphos-methyl. Pre-exposure to PBO increased susceptibility to deltamethrin in both species. Both kdr west and east were detected in Anopheles arabiensis (L1014S freq = 0.083, L1014F freq = 0.063) and Anopheles quadriannulatus (L1014S freq = 0.074, L1014F freq = 0.043) at low frequencies. Anopheles funestus sensu stricto and Anopheles rivolurum had the presence of CYP6Pa, CYP6Pb, 6.5kb S.V and GSTe2-L119F, with low allele frequencies. There were no significant associations between the genotypes and phenotypic profile.

CONCLUSIONS

Malaria vectors in Kwale are resistant to pyrethroids. PBO fully restored susceptibility, indicating this resistance could be caused by metabolic mechanism. The presence of kdr and metabolic resistance alleles suggests a recent selection on Anopheles mosquitoes. Pyrethroid-only nets may not fully ensure community protection against malaria in coastal Kenya due to resistance. Operational failure remains uncertain, requiring further studies. Net distribution programs should consider pyrethroid-PBO nets to enhance malaria control effectiveness.

Susceptibility profile of Anopheles and target site resistance mechanism against organophosphates in Cameroon

Escalating pyrethroid resistance in malaria vectors jeopardizes vector control, necessitating the use of alternative insecticides such as pirimiphos-methyl (organophosphate) for indoor residual spraying (IRS). Tracking the spread of resistance and elucidating its molecular basis are essential for effective resistance management against these insecticides. This study monitored resistance to two organophosphates, malathion (MA) and pirimiphos methyl (PM), in three malaria vectors (Anopheles gambiae s.s., An. coluzzii, and An. funestus s.s.) across Cameroon and explored related resistance mechanisms. WHO tube assays revealed that An. funestus s.s. populations were fully susceptible to both organophosphates; An. coluzzii populations were either fully susceptible (North) or potentially resistant (South; 97% mortality). In contrast, the two An. gambiae s.s. populations in this study were resistant: in the rural agricultural hotspots of Mangoum (94% mortality to PM; 50% to MA) and in peri-urban cultivated location of Nkolondom, which exhibited the highest resistance to both PM (80% mortality) and MA (46% mortality), associated with recorded use of organophosphates by farmers. Genotyping the Ace-1 markers revealed a close association with susceptibility profile, as no resistance allele was observed in An. funestus s.s. and in the northern population of An. coluzzii and a very low frequency in Njombe (3%). In contrast, a higher frequency of Ace-1R was observed in An. gambiae s.s. with a significant association observed with resistance (PM: OR = 20.33, P = 0.04; MA: OR = 98.33, P = 0.0019). Furthermore, analysis of 100 Ace-1 clones showed copy number variation was linked to resistance, as resistant mosquitoes displayed higher copy numbers compared to susceptible individuals. These findings suggest that malaria control with organophosphate-based IRS is a viable alternative in Cameroon; however, it will be necessary to consider the distribution of species and the development of resistance.

Adjusting vector surveillance for human behaviors reveals Anopheles funestus drove a resurgence in malaria despite IRS with clothianidin in Uganda

After remarkable success following the implementation of indoor residual spraying (IRS) and repeated rounds of universal distribution of insecticidal treated nets in Tororo District, eastern Uganda, a switch to clothianidin-based IRS in March 2020 was associated with a resurgence of malaria transmission. A previous study suggested Anopheles funestus may be driving the resurgence. This study was undertaken to assess the role of An. funestus in the resurgence and improve our understanding of how human-vector interaction affects malaria transmission in settings with extensive vector control. Using human landing catches and human behavioral observations, we found An. funestus infective biting, calculated from human-behavior adjusted biting rates and species-specific sporozoite rates, was 4.3 (95% Confidence Interval [CI]: 1.81 to 10.33) times higher after multiple rounds of clothianidin-based IRS when transmission was high and then dropped off markedly with a switch back to the organophosphate Actellic in March 2023. This finding was bolstered by a causal analysis showing a link between clothianidin-based IRS and 8.6 (95% CI: 2.0 to 37.0) times higher human-behavior adjusted human biting rates due to An. funestus. These findings highlight the importance of integrating monitoring of human-vector interaction and vector bionomics when introducing or evaluating changes in vector control interventions.

Age structure and parity status determination of Afrotropical malaria vectors using MALDI-TOF MS

The age structure of a mosquito population helps estimate the proportion of vectors capable of transmitting malaria. Many malaria transmission models rely on mosquito longevity as key parameter. However, these are rarely measured in the field due to lack of a reliable and scalable age-grading method. An accurate method could improve predictions of malaria risk and the impact assessment of interventions. This study aimed to investigate the use of Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) for malaria vector age-grading using insectary-reared and wild-caught mosquitoes. Anopheles gambiae s.s. mosquitoes were reared in the insectary to different known physiological and chronological ages to evaluate if MALDI-TOF MS could be used to distinguish between different age groups. Wild mosquitoes were collected from Mozambique and Kenya and dissected to determine their parity status. Reference spectra were obtained from mosquito's cephalothorax and used to create predictive databases which were validated using independent samples. MALDI-TOF MS identified the physiological and chronological age of insectary-reared mosquitoes with 94.52% and 77% accuracy respectively. Field-collected mosquitoes were primarily An. funestus s.s. and An. gambiae s.s. Parity prediction accuracy was between 81% and 87%. MALDI-TOF MS was able to distinguish and differentiate mosquitoes based on their age structure (chronological and physiological) and parity status.

Impact of Late-Rainy Season Indoor Residual Spraying on Holoendemic Malaria Transmission: A Cohort Study in Northern Zambia

BACKGROUND

Indoor residual spraying (IRS) is a malaria control strategy implemented before the rainy season. Nchelenge District, Zambia, is a holoendemic setting where IRS has been conducted since 2008 with little impact on malaria incidence or parasite prevalence. Pre-rainy season IRS may not reduce the post-rainy season peak abundance of the major vector Anopheles funestus.

METHODS

A controlled, pretest-posttest, prospective cohort study assessed the impact of late-rainy season IRS on malaria prevalence, incidence, hazard, and vector abundance. A total of 382 individuals were enrolled across 4 household clusters, of which 2 were sprayed in April 2022 toward the end of the rainy season. Monthly household and individual surveys and indoor overnight vector collections were conducted through August 2022. Multivariate regression and time-to-event analyses estimated the impact of IRS on outcomes measured by rapid diagnostic tests, microscopy, and quantitative polymerase chain reaction.

RESULTS

Among participants, 72% tested positive by rapid diagnostic test at least once, and incidence by microscopy was 3.4 infections per person-year. Residing in a household in a sprayed area was associated with a 52% reduction in infection hazard (hazards ratio, 0.48; 95% CI, .29-.78) but not with changes in incidence, prevalence, or vector abundance. The study-wide entomologic inoculation rate was 34 infectious bites per person per year.

CONCLUSIONS

Monthly tracking of incidence and prevalence did not demonstrate meaningful changes in holoendemic transmission intensity. However, hazard of infection, which provides greater power for detecting changes in transmission, demonstrated that late-rainy season IRS reduced malaria risk.

Effect of a novel house design (star home) on indoor malaria mosquito abundance in rural Tanzania: secondary outcomes of an open-label, household, randomised controlled trial

BACKGROUND

Screening houses can reduce malaria transmission in sub-Saharan Africa. Our study evaluated whether a novel screened house design (star home) with bedrooms on the second storey reduced indoor mosquito abundance compared with traditional houses in Mtwara, Tanzania.

METHODS

In this open-label, household, randomised controlled trial, indoor mosquito abundance was assessed in 110 star homes and 110 neighbouring traditional houses in 59 villages from Jan 5, 2022, to Dec 20, 2023. Mosquitoes were collected using US Centers for Disease Control light traps every 7 weeks. Anopheles gambiae and Anopheles funestus species were identified using PCR and Plasmodium falciparum sporozoites detected using ELISA. Nightly temperature, CO2 concentrations, and duration of door opening was recorded. Differences between study groups were analysed using generalised linear mixed-effects models. The trial is registered with ClinicalTrials.gov (NCT04529434).

FINDINGS

Of 9290 mosquitoes collected, 1899 were A gambiae, 69 were A funestus, and 7322 Culex species, mainly Culex quinquefasciatus. Star homes had 51% less A gambiae (adjusted risk ratio [RR] 0·49, 95% CI 0·35 to 0·69; p<0·0001) and 61% less Culex species (RR 0·39, 0·32 to 0·48; p<0·0001) than traditional houses. At night, star homes were 0·5°C cooler (95% CI 0·2 to 0·9; p=0·010), with similar concentrations of CO2 (-7 ppm, 95% CI -19 to 6; p=0·285) and had external doors open 53% less time than traditional houses (7·5 min/h vs 16·2 min/h; p<0·0001).

INTERPRETATION

Star homes reduced indoor mosquito abundance and malaria transmission risk compared with traditional houses, demonstrating the protective efficacy of houses that are well screened and air permeable in rural Africa.

FUNDING

Hanako Foundation, Singapore.

Understudied anophelines may sustain residual transmission during the dry season in a pre-elimination setting in southern Zambia

Malaria control is a public health priority but common control methods like indoor residual spraying and the use of bednets do not target outdoor-biting vectors. In settings with seasonal residual malaria transmission, we lack critical knowledge regarding anopheline species composition and their role in transmission. This study aimed to determine relative seasonal vector species abundance and associated household level factors in a low transmission setting in Choma District, Zambia. Indoor and outdoor adult vector collections were embedded in a community-based longitudinal cohort study in 60 households that were visited monthly for 2 years between 2018 and 2020. Surveys conducted at the time of trap placement collected information on animal ownership, housing structure, and the receipt of malaria interventions. Anopheline species identities were molecularly confirmed by polymerase chain reaction, and enzyme-linked immunosorbent assay was used to detect the circumsporozoite protein of Plasmodium falciparum. Generalized linear mixed effects negative binomial regression with zero-inflation models were used to describe the relationship between risk factors and the outcome of monthly anopheline counts at each household, stratified by season. The study collected 1,532 female anophelines, 76% of which were caught outdoors. The relative abundance differed by season: in the dry season, 90% of female anophelines were caught outdoors. Anopheles arabiensis was overall the most common vector, but made up only 28% of outdoor collections; the remainder were understudied anophelines including An. coustani, An. leesoni, An. rufipes, and An. squamosus. The only Plasmodium falciparum-infected mosquito was an An. squamosus that was caught outdoors. Owning more goats was associated with a 3.5 (IRR 4.47, 95% confidence interval [CI]: 2.00, 10.01) and 7.7 (IRR 8.73, 95% CI: 4.40, 17.32) times increase in indoor and outdoor anopheline collections in the dry season and a 1.2 (IRR 2.18, 95% CI: 1.12, 4.23) times higher risk of outdoor anophelines in the rainy season. Improved housing structure was associated with fewer indoor anophelines in the rainy season, but not during dry season or outdoor anopheline abundance any time of year. Vector control in this low transmission setting, therefore, needs to target anopheline mosquitoes year-round, must be expanded to target traditionally zoophillic mosquitoes, and leverage known risk factors when selecting methods of control.

Anopheles mosquito fauna, blood meal sources and transmission intensity from high and moderate malaria endemic areas of Ethiopia

This study investigates malaria vector dynamics in Lare and Asendabo, southwestern Ethiopia, areas with limited entomological information. From July to December 2021, mosquitoes were collected from 56 randomly selected houses using Pyrethrum Spray Catches, CDC light traps, and Human Landing Catches. Blood meal sources (human, bovine, goat) and circumsporozoite proteins (CSP) were detected via Enzyme-linked immunosorbent assays (ELISA), and mosquitoes were analyzed for physiological state, and Plasmodium infection. The entomological inoculation rates (EIR) for Anopheles gambiae s.l. and An. funestus were calculated, and species identification was performed by PCR on CSP-positive and randomly selected samples. A total of 2,565 mosquitoes from four Anopheles species were collected, with An. gambiae s.l. dominating. Indoor collected anophelines (53%) surpassed outdoor (47%). PCR confirmed An. gambiae s.l. as An. arabiensis and An. funestus as An. funestus and An. leesoni. Twenty two An. funestus tested positive for Plasmodium while Plasmodium-positive pools also included, An. gambiae s.l. (15), An. coustani (2), and An. pharoensis (1). The P. falciparum EIR for An. gambiae s.l. in Asendabo was 1.39 bites/person/month, while An. funestus had the highest bite rate (10.52 bites/person/month). Mixed blood meals and zoophilic behaviour were common, underscoring the need for species-specific, spatio-temporal vector control strategies.

Bionomics and distribution of malaria vectors in Kisumu city, Western Kenya: implications for urban malaria transmission

BACKGROUND

Increasing unplanned urbanization in tropical Africa may create new niches for malaria vectors, raising transmission risk, yet control efforts focus on rural ecosystems. Understanding mosquito diversity, ecology and biting behaviour in urban areas is crucial for effective control. This study assessed Anopheles diversity, abundance, behaviour, and Plasmodium infection rates in Kisumu city, Kenya.

METHODS

Indoor and outdoor host-seeking and resting adult mosquitoes were collected using CDC miniature light traps (CDC-LT) and Prokopack aspirators along an urban-rural transect. Anophelines were identified morphologically, with Anopheles gambiae sensu lato (s.l.) and Anopheles funestus group further distinguished to siblings using polymerase chain reaction (PCR). Sporozoite infection rates were determined using a multiplexed real-time quantitative PCR (qPCR) assay.

RESULTS

A total of 3,394 female Anopheles mosquitoes were collected: An. gambiae s.l. (68%), An. funestus s.l. (19.8%), Anopheles coustani (7.8%), Anopheles pharoensis (2.6%), Anopheles maculipalipis (1.6%), and Anopheles leesoni (0.2%). All six species were found in urban zone, but only three were in peri-urban and rural sites. Overall, urban collection accounted for 55.5% of mosquitoes, followed by peri-urban (30%) and rural sites (14.5%). Anopheles arabiensis dominated urban (84.3%) and peri-urban (89%) sites, while An. gambiae sensu stricto (s.s.) was predominant in rural zone (60.2%) alongside An. arabiensis (39.7%). Anopheles funestus was predominant in peri-urban (98.4%) and rural (85.7%) areas, while An. leesoni accounted for 1.6% and 14.3%, respectively. In urban areas, all An. funestus s.l. samples were An. funestus s.s.. Most (55.5%) of Anopheles mosquitoes were collected indoors, while secondary vectors were mainly outdoors. Overall, sporozoite rates were higher outdoors (3.5%) than indoors (1.45%) in rural areas. Indoor rates were 2.5% (An. funestus), 1.4% (An. gambiae s.s.), and 1% (An. arabiensis). Outdoors, An. gambiae had 5.3%, and An. arabiensis 2.1%. In peri-urban areas, An. gambiae had 2.3%. No sporozoites were found in urban samples.

CONCLUSION

The study highlights a shift in Anopheles diversity towards urban areas with increased outdoor activity and outdoor malaria transmission in rural and peri-urban areas, underscoring the need for tools targeting outdoor-biting mosquitoes. The presence of An. funestus in urban settings emphasizes the need for sustained entomological surveillance to inform integrated vector control.

Multiple insecticide resistance in Anopheles funestus from Mopeia, Central Mozambique

BACKGROUND

The main malaria vector control methods implemented in Mozambique are insecticide-treated nets (ITN's) and indoor residual spraying (IRS). These insecticide-based interventions are currently threatened by the rapidly spreading insecticide resistance in several major malaria vectors. Monitoring of insecticide resistance is necessary to inform the selection of insecticides by control programmes. This study describes the insecticide resistance profiles of the main malaria vector, Anopheles funestus sensu lato. in Mopeia district, a malaria holoendemic area of the Zambezia province of Mozambique.

METHODS

Anopheles adults and larvae were collected from 15 sentinel sites across the district between October 2021 and September 2022. Wild-caught, unfed female adults were collected using CDC-light traps and pooled over three days before exposure to the test insecticide. For mosquitoes collected as larvae, F0 adults aged 3-5 days post-emergence were used for insecticide susceptibility testing. Resistance to bendiocarb, DDT, deltamethrin and pirimiphos-methyl was evaluated using the standard WHO tube bioassay. The mechanism of resistance was probed using the PBO (piperonyl butoxide) synergistic bioassay. The presence and frequency of different genetic mutations associated with insecticide resistance was assessed using polymerase chain reaction, including A296S-Rdl, L119F-GSTe2 and 6.5 kb SV (structural variation) insertion.

RESULTS

A total of 1349 female Anopheles mosquitoes (controls included) were used for susceptibility tests with discriminating insecticide concentrations. Phenotypic resistance to bendiocarb, DDT, deltamethrin and pirimiphos-methyl was observed, with 37%, 79%, 14% and 67% mortality rate respectively. Pre-exposure to PBO partially restored susceptibility to deltamethrin to a mortality rate of 80%. The frequency of the insecticide resistance mutations was 0.49, 0.05 and 0.92, for A296S-Rdl, L119F-GSTe2 and 6.5 kb SV insertion, respectively.

CONCLUSION

Malaria vectors in Mopeia exhibit resistance to all four major public health insecticide classes: pyrethroids, organophosphates, organochlorides and carbamates. This highlights the urgent need to adopt new insecticide classes for vector control interventions. The partial restoration of susceptibility by PBO suggests resistance is being driven by various mechanisms including the involvement of metabolic resistance through cytochrome P450 monooxygenase enzymes and glutathione S-transferases.

Implications for malaria transmission: a cross-sectional study on the bionomics and susceptibility of local malaria vectors in urban and periurban settings of Ndola district

OBJECTIVES

To assess vector behaviour and phenotypic resistance for effective vector control programming.

DESIGN

This was a cross-sectional study.

SETTING

This study was conducted in the urban and periurban areas of Ndola district, Zambia.

PARTICIPANTS/STUDY UNITS

A total of 166 houses were selected for adult mosquito collection, and an additional 60 collection efforts were made for larval collection from potential larval habitats.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome was the behaviour of the malaria vectors, and the secondary outcome was their phenotypic resistance status.

RESULTS

The main breeding sites identified were irrigation trenches (4.67 larvae/dip) and garden ponds (2.72 larvae/dip) created from extensive urban agriculture practices. Anopheles funestus sensu stricto (An. funestus s.s) and Anopheles gambiae sensu stricto (An. gambiae s.s) were found to coexist in all the four sites, with An. funestus s.s identified as the most dominant malaria vector. Densities of An. gambiae s.s, seeking a blood meal (χ2=12.566, df=3, p=0.001) and resting indoors (Z=56.5, p=0.019), were found to be higher in urban than periurban sites compared with An. funestus s.s, which had similar distribution across the study sites. Sprayed houses were significantly associated with reduced mosquito numbers (B=-0.956, incidence rate ratio=0.384, p=0.001). Anopheles gambiae was fully susceptible to organophosphates and neonicotinoids but highly resistant to pyrethroids, carbamates and organochlorines.

CONCLUSIONS

The emergence of An. funestus s.s in an area previously dominated by An. gambiae s.s and its coexistence with An. gambiae s.s in the dry season pose a risk of sustaining malaria transmission all year round. Agricultural practices in urban areas resulted in highly productive mosquito breeding sites; thus, there is a need for targeted vector control.

Targeting malaria in high-risk populations in low endemic regions in northern Namibia: a quasi-experimental controlled trial to reduce malaria in seasonal agricultural workers and cattle herders

BACKGROUND

Agricultural worksites are rarely targeted by malaria control programmes, yet may play a role in maintaining local transmission due to workers' high mobility, low intervention coverage and occupational exposures.

METHODS

A quasi-experimental controlled intervention study was carried out in farming and cattle herding populations in northern Namibia to evaluate the impact of a targeted malaria intervention package. Eight health facility catchment areas in Zambezi and Ohangwena Regions were randomised to an intervention arm and eligible individuals within worksites in intervention areas received targeted drug administration with artemether-lumefantrine, mop-up indoor residual spraying and long-lasting insecticidal nets, combined with distribution of topical repellent in Zambezi Region. Impact on malaria outcomes and intervention coverage was evaluated over a single transmission season using pre-intervention and post-intervention cross-sectional surveys in a random subset of worksites and community incidence from passively detected cases. Entomological collections and residual efficacy assays on canvas and tarpaulin were conducted.

RESULTS

Delivery of a single intervention round was associated with a reduction in the prevalence of malaria (OR 0.24, 95% CI 0.1 to 0.5; risk difference (RD) -6.0%, 95% CI -9.4 to -2.8). Coverage of at least one intervention increased (RD 51.6%, 95% CI 44.4 to 58.2) among the target population in intervention compared with control areas. This effect was largely driven by results in Zambezi Region, which also observed a decline in community incidence (-1.29 cases/1000 person-weeks, 95% CI -2.2 to -0.3). Residual efficacy of pirimiphos-methyl (Actellic) on tarpaulin and canvas was high at 24hours but declined to 44.6% at 4 months.

CONCLUSION

The study shows that targeted delivery of malaria interventions to cattle herders and agricultural workers at worksites has potential to impact local transmission. Findings highlight the need for further research on the role of key populations in Plasmodium falciparum transmission in Namibia.

TRIAL REGISTRATION NUMBER

NCT04094727.

Metabolic resistance to pyrethroids with possible involvement of non-coding ribonucleic acids in Anopheles funestus, the major malaria vector in western Kenya

BACKGROUND

The resurgence of Anopheles funestus, a dominant vector of human malaria in western Kenya was partly attributed to insecticide resistance. However, evidence on the molecular basis of pyrethroid resistance in western Kenya is limited. Here, we reported metabolic resistance mechanisms and demonstrated that multiple non-coding Ribonucleic Acids (ncRNAs) could play a potential role in An. funestus resistance to pyrethroid in western Kenya. Anopheles funestus mosquitoes were sampled using aspiration methods in Bungoma, Teso, Siaya, Port Victoria and Kombewa in western Kenya. The F1 progenies were exposed to deltamethrin (0.05%), permethrin (0.75%), DDT (4%) and pirimiphos-methyl (0.25%) following WHO test guidelines. A synergist assay using piperonyl butoxide (PBO) (4%) was conducted to determine cytochrome P450s' role in pyrethroid resistance. RNA-seq was conducted on a combined pool of specimens that were resistant and unexposed, and the results were compared with those of the FANG susceptible reference strain. This approach aimed to uncover the molecular mechanisms underlying the observed phenotypic pyrethroid resistance.

RESULTS

Pyrethroid resistance was observed in all sites with an average mortality rate (MR) of 57.6%. Port Victoria had the highest level of pyrethroid resistance to permethrin (MR = 53%) and deltamethrin (MR = 11%. Teso had the lowest level of resistance to permethrin (MR = 70%) and deltamethrin (MR = 87%). Resistance to DDT was observed only in Kombewa (MR = 89%) and Port Victoria (MR = 85%). A full susceptibility to P-methyl (0.25%) was observed in all sites. PBO synergist assay revealed high susceptibility (> 98%) to pyrethroids in all the sites except for Port Victoria (MR = 96%). Whole transcriptomic analysis showed that most gene families associated with pyrethroid resistance comprised non-coding RNAs (67%), followed by immunity proteins (10%), cytochrome P450s (6%), cuticular proteins (5%), olfactory proteins (4%), glutathione S-transferases (3%), UDP-glycosyltransferases (2%), ATP-binding cassettes (2%) and carboxylesterases (1%).

CONCLUSION

This study unveils the molecular basis of insecticide resistance in An. funestus in western Kenya, highlighting for the first time the potential role of non-coding RNAs alongside metabolic detoxification in pyrethroid resistance. Targeting non-coding RNAs for intervention development could help in insecticide resistance management.

Malaria prevalence, transmission potential and efficacy of artemisinin-based combination therapy in the Kenyan Central highlands: a zone previously characterized as malaria-free

BACKGROUND

The current study sought to re-evaluate malaria prevalence, susceptibility to artemisinin-based combination therapy (ACT), transmission patterns and the presence of malaria vectors in the Kikuyu area of the Kenyan Central highlands, a non-traditional/low risk malaria transmission zone where there have been anecdotal reports of emerging malaria infections.

METHODS

Sampling of adult mosquitoes was done indoors, while larvae were sampled outdoors in June 2019. The malaria clinical study was an open label non-randomized clinical trial where the efficacy of one ACT drug, was evaluated in two health facilities. Microscopy was used at the facility while nested 18 s rRNA subunit gene PCR amplification and MSP-1 and MSP-2 family alleles genotyping was done in the laboratory. Anti-malarial resistance gene markers Pfk13 and Pfmdr1 were profiled.

RESULTS

Anopheles funestus mosquitoes were the predominant vectors at 76.35% of all larvae collections (N = 148). Only two non-blood fed, parasites negative adult mosquitoes were collected from houses sampled. Parasitological analysis of the 838 patients screened resulted in 41 positives whose treatment outcome was 100% Adequate Clinical and Parasitological Response (ACPR). From the 35 positive samples genotyped, 29 (82.9%) were polyclonal. The overall mean MOI was 2.8 (95% CI 2.36-3.35). The MOI for msp-1 and msp-2 genes, was 2.02 (95% CI 0.72-2.27) and 2.9 (95% CI 2.22-3.55), and parasite strains range of 1-3 and 1-7, respectively. Polyclonal variation in the two genes was at 76.4% and 70.3%, respectively. The Pfk13 gene revealed no single nucleotide polymorphisms (SNP) associated with suspected artemisinin resistance nor was there any pfmdr1 N86 mutant allele detected.

CONCLUSION

The Plasmodium infections positivity rate observed in the study site was very low but significant. A proportion of participants who tested positive did not report recent history of travel. This observation together with the finding of competent known vectors can probably suggest that several of the cases could have been acquired and transmitted locally. The observed genetic diversity and polyclonal variations was on the contrary and suggest that these are imported cases. This however does not rule out a likely changing malaria transmission scenario in this zone, thus the need for further investigations.

A matter of timing: Biting by malaria-infected Anopheles mosquitoes and the use of interventions during the night in rural south-eastern Tanzania

Knowing when and where infected mosquitoes bite is required for estimating accurate measures of malaria risk, assessing outdoor exposure, and designing intervention strategies. This study combines secondary analyses of a human behaviour survey and an entomological survey carried out in the same area to estimate human exposure to malaria-infected Anopheles mosquitoes throughout the night in rural villages in south-eastern Tanzania. Mosquitoes were collected hourly from 6PM to 6AM indoors and outdoors by human landing catches in 2019, and tested for Plasmodium falciparum sporozoite infections using ELISA. In nearby villages, a trained member in each selected household recorded the whereabouts and activities of the household members from 6PM to 6AM in 2016 and 2017. Vector control use was high: 99% of individuals were reported to use insecticide-treated nets and a recent trial of indoor residual spraying had achieved 80% coverage. The risk of being bitten by infected mosquitoes outdoors, indoors in bed, and indoors but not in bed, and use of mosquito nets was estimated for each hour of the night. Individuals were mainly outdoors before 9PM, and mainly indoors between 10PM and 5AM. The main malaria vectors caught were Anopheles funestus sensu stricto and An. arabiensis. Biting rates were higher in the night compared to the evening or early morning. Due to the high use of ITNs, an estimated 85% (95% CI 81%, 88%) of all exposure in children below school age and 76% (71%, 81%) in older household members could potentially be averted by ITNs under current use patterns. Outdoor exposure accounted for an estimated 11% (8%, 15%) of infective bites in children below school age and 17% (13%, 22%) in older individuals. Maintaining high levels of ITN access, use and effectiveness remains important for reducing malaria transmission in this area. Interventions against outdoor exposure would provide additional protection.

Temporal evolution of insecticide resistance and bionomics in Anopheles funestus, a key malaria vector in Uganda

Insecticide resistance escalation is decreasing the efficacy of vector control tools. Monitoring vector resistance is paramount in order to understand its evolution and devise effective counter-solutions. In this study, we monitored insecticide resistance patterns, vector population bionomics and genetic variants associated with resistance over 3 years from 2021 to 2023 in Uganda. Anopheles funestus s.s was the predominant species in Mayuge but with evidence of hybridization with other species of the An. funestus group. Sporozoite infection rates were relatively very high with a peak of 20.41% in March 2022. Intense pyrethroid resistance was seen against pyrethroids up to 10-times the diagnostic concentration but partial recovery of susceptibility in PBO synergistic assays. Among bednets, only PBO-based nets (PermaNet 3.0 Top and Olyset Plus) and chlorfenapyr-based net (Interceptor G2) had high mortality rates. Mosquitoes were fully susceptible to chlorfenapyr and organophosphates, moderately resistant to clothianidin and resistant to carbamates. The allele frequency of key P450, CYP9K1, resistance marker was constantly very high but that for CYP6P9A/b were very low. Interestingly, we report the first detection of resistance alleles for Ace1 gene (RS =  ~ 13%) and Rdl gene (RS =  ~ 21%, RR =  ~ 4%) in Uganda. The qRT-PCR revealed that Cytochrome P450s CYP9K1, CYP6P9A, CYP6P9b, CYP6P5 and CYP6M7 were consistently upregulated while a glutathione-S-transferase gene (GSTE2) showed low expression. Our study shows the complexity of insecticide resistance patterns and underlying mechanisms, hence constant and consistent spatial and temporal monitoring is crucial to rapidly detect changing resistance profiles which is key in informing deployment of counter interventions.

Insights into the biology and insecticide susceptibility of the secondary malaria vector Anopheles parensis in an area with long-term use of insecticide-treated nets in northwestern Tanzania

BACKGROUND

The Anopheles funestus group includes at least 11 sibling species, with Anopheles funestus Giles being the most studied and significant malaria vector. Other species, like Anopheles parensis, are understudied despite their potential role in transmission. This article provides insights into the biology and insecticide susceptibility of An. parensis, with observations of its densities in northwestern Tanzania.

METHODS

Mosquitoes were collected in three villages in Misungwi district, northwestern Tanzania, using CDC light traps and battery-powered aspirators indoors and human-baited double net traps outdoors. Female Anopheles adults were morphologically sorted and identified by PCR, and a subset was tested by ELISA for vertebrate blood meal sources and Plasmodium sporozoite infections. Insecticide susceptibility was assessed using the WHO protocol (2nd edition, 2018). Unfed females were dissected to assess parity, gonotrophic status and insemination status, while blood-fed females were monitored for oviposition to estimate egg counts. The prevalence of An. parensis was generally < 24% across all sites, except in Ngaya village, where it unexpectedly constituted 84% of PCR-amplified An. funestus sensu lato. This species was present in both indoor and outdoor collections, yet the females exclusively fed on non-human vertebrates, with no human blood meals detected. Parity rates were approximately 49% for resting and 46% for host-seeking females, with slightly higher percentages of both parous and inseminated females in the dry season compared to the wet season. Most parous females had oviposited once or twice, with those in the dry season ovipositing significantly more eggs. The average wing length of female An. parensis was 2.93 mm, and there was no significant impact of body size on parity, fecundity or insemination. The An. parensis mosquitoes were fully susceptible to pyrethroids, carbamates, organophosphates and organochlorides.

RESULTS

The prevalence of An. parensis was generally < 24% across all sites, except in Ngaya village, where it unexpectedly constituted 84% of PCR-amplified An. funestus sensu lato. This species was present in both indoor and outdoor collections, yet the females exclusively fed on non-human vertebrates, with no human blood meals detected. Parity rates were approximately 49% for resting and 46% for host-seeking females, with slightly higher percentages of both parous and inseminated females in the dry season compared to the wet season. Most parous females had oviposited once or twice, with those in the dry season ovipositing significantly more eggs. The average wing length of female An. parensis was 2.93 mm, and there was no significant impact of body size on parity, fecundity or insemination. The An. parensis mosquitoes were fully susceptible to pyrethroids, carbamates, organophosphates and organochlorides..

CONCLUSION

This study offers insights into the behaviours and insecticide susceptibility of An. parensis. Primarily feeding on non-human hosts, An. parensis is less significant in malaria transmission than more anthropophilic vectors. Unlike the pyrethroid-resistant An. funestus sensu stricto, An. parensis remains fully susceptible to public health insecticides despite the use of insecticidal bed nets. These findings provide a foundation for future research and may inform control strategies targeting residual malaria transmission involving An. parensis.

Two highly selected mutations in the tandemly duplicated CYP6P4a and CYP6P4b genes drive pyrethroid resistance in Anopheles funestus in West Africa

BACKGROUND

Gaining a comprehensive understanding of the genetic mechanisms underlying insecticide resistance in malaria vectors is crucial for optimising the effectiveness of insecticide-based vector control methods and developing diagnostic tools for resistance management. Considering the heterogeneity of metabolic resistance in major malaria vectors, the implementation of tailored resistance management strategies is essential for successful vector control. Here, we provide evidence demonstrating that two highly selected mutations in CYP6P4a and CYP6P4b are driving pyrethroid insecticide resistance in the major malaria vector Anopheles funestus, in West Africa.

RESULTS

Continent-wide polymorphism survey revealed escalated signatures of directional selection of both genes between 2014 and 2021. In vitro insecticide metabolism assays with recombinant enzymes from both genes showed that mutant alleles under selection exhibit higher metabolic efficiency than their wild-type counterparts. Using the GAL4-UAS expression system, transgenic Drosophila flies overexpressing mutant alleles exhibited increased resistance to pyrethroids. These findings were consistent with in silico predictions which highlighted changes in enzyme active site architecture that enhance the affinity of mutant alleles for type I and II pyrethroids. Furthermore, we designed two DNA-based assays for the detection of CYP6P4a-M220I and CYP6P4b-D284E mutations, showing their current confinement to West Africa. Genotype/phenotype correlation analyses revealed that these markers are strongly associated with resistance to types I and II pyrethroids and combine to drastically reduce killing effects of pyrethroid bed nets.

CONCLUSIONS

Overall, this study demonstrated that CYP6P4a and CYP6P4b contribute to pyrethroid resistance in An. funestus and provided two additional insecticide resistance molecular diagnostic tools that would contribute to monitoring and better management of resistance.

Genome-wide association studies unveil major genetic loci driving insecticide resistance in Anopheles funestus in four eco-geographical settings across Cameroon

BACKGROUND

Insecticide resistance is jeopardising malaria control efforts in Africa. Deciphering the evolutionary dynamics of mosquito populations country-wide is essential for designing effective and sustainable national and subnational tailored strategies to accelerate malaria elimination efforts. Here, we employed genome-wide association studies through pooled template sequencing to compare four eco-geographically different populations of the major vector, Anopheles funestus, across a South North transect in Cameroon, aiming to identify genomic signatures of adaptive responses to insecticides.

RESULTS

Our analysis revealed limited population structure within Northern and Central regions (FST<0.02), suggesting extensive gene flow, while populations from the Littoral/Coastal region exhibited more distinct genetic patterns (FST>0.049). Greater genetic differentiation was observed at known resistance-associated loci, resistance-to-pyrethroids 1 (rp1) (2R chromosome) and CYP9 (X chromosome), with varying signatures of positive selection across populations. Allelic variation between variants underscores the pervasive impact of selection pressures, with rp1 variants more prevalent in Central and Northern populations (FST>0.3), and the CYP9 associated variants more pronounced in the Littoral/Coastal region (FST =0.29). Evidence of selective sweeps was supported by negative Tajima's D and reduced genetic diversity in all populations, particularly in Central (Elende) and Northern (Tibati) regions. Genomic variant analysis identified novel missense mutations and signatures of complex genomic alterations such as duplications, deletions, transposable element (TE) insertions, and chromosomal inversions, all associated with selective sweeps. A 4.3 kb TE insertion was fixed in all populations with Njombe Littoral/Coastal population, showing higher frequency of CYP9K1 (G454A), a known resistance allele and TE upstream compared to elsewhere.

CONCLUSION

Our study uncovered regional variations in insecticide resistance candidate variants, emphasizing the need for a streamlined DNA-based diagnostic assay for genomic surveillance across Africa. These findings will contribute to the development of tailored resistance management strategies crucial for addressing the dynamic challenges of malaria control in Cameroon.

Genomic diversity of the African malaria vector Anopheles funestus

Anopheles funestus s.s. is a formidable human malaria vector across sub-Saharan Africa. To understand how the species is evolving, especially in response to malaria vector control, we sequenced 656 modern specimens (collected 2014-2018) and 45 historic specimens (collected 1927-1967) from 16 African countries. We find high levels of genetic variation with clear and stable continental patterns. Six segregating inversions might be involved in adaptation of local ecotypes. Strong recent signals of selection centred on canonical insecticide resistance genes are shared by multiple populations. A promising gene drive target in An. gambiae is highly conserved in An. funestus. This work represents a significant advance in our understanding of the genetic diversity and population structure of An. funestus and will enable smarter targeted malaria control.

The bionomics of Anopheles arabiensis and Anopheles funestus inside local houses and their implications for vector control strategies in areas with high coverage of insecticide-treated nets in South-eastern Tanzania

BACKGROUND

Residual malaria transmissions in Africa may be associated with improved coverage of insecticide-treated nets, house features, and livestock husbandry. These human-land use activities may drive the ecology and behaviour of malaria vectors which sustain residual malaria transmission. This study was conducted to assess changes in the ecology and behaviour of Anopheles funestus and Anopheles arabiensis in villages with high coverage of insecticide-treated nets to guide the selection of complementary vector control strategies against residual malaria transmission.

METHODS

Mosquitoes were collected using a CDC-light trap, miniaturized double net trap, and Prokopack aspirator from 222 households in three villages (Ebuyu, Chirombora, and Mzelezi) within Kilombero Valley. Anopheles mosquitoes were morphologically identified to their physiological status and species-complex levels. A sub-sample of Anopheles mosquitoes was exposed to laboratory analyses of sibling species, host preference, and sporozoite rates. Additionally, the local houses were geo-referenced using Global Positioning Systems (GPS) devise, and house features were recorded and associated with vector abundance.

RESULTS

The population of An. funestus s.s was abundant with high Plasmodium sporozoite rates inside houses compared to An. arabiensis. However, these vector species equally blood-fed on humans inside houses, but they also flexibly mixed human and animal blood meal. Fewer An. funestus were caught in houses with metal- than grass roofs and houses with and without animals. Contrastingly, fewer An. arabiensis were caught from houses with screened eaves compared to houses with open eaves.

CONCLUSIONS

This study confirms that An. funestus dominates residual malaria transmission over An. arabiensis. These vector species exhibit anthropophily and opportunistic blood-feeding behaviour in areas with high coverage of insecticide-treated nets, but they numerically respond differently to local house improvements. These results imply that integrating mosquito-proof houses, improved insecticide-treated nets, and livestock-based interventions could effectively reduce and eventually eliminate residual malaria transmission.

Discovery of Knock-Down Resistance in the Major African Malaria Vector Anopheles funestus

A major insecticide resistance mechanism in insect pests is knock-down resistance (kdr) caused by mutations in the voltage-gated sodium channel (Vgsc) gene. Despite being common in most malaria Anopheles vector species, kdr mutations have never been observed in Anopheles funestus, the principal malaria vector in Eastern and Southern Africa, with resistance mainly being conferred by detoxification enzymes. In a parallel study, we monitored 10 populations of An. funestus in Tanzania for insecticide resistance unexpectedly identified resistance to a banned insecticide, DDT, in the Morogoro region. Through whole-genome sequencing of 333 An. funestus samples from these populations, we found eight novel amino acid substitutions in the Vgsc gene, including the kdr variant, L976F (equivalent to L995F in An. gambiae), in tight linkage disequilibrium with another (P1842S). The mutants were found only at high frequency in one region and were accompanied by weak signatures of a selective sweep, with a significant decline between 2017 and 2023. Notably, kdr L976F was strongly associated with survivorship to exposure to DDT insecticide, while no clear association was noted with a pyrethroid insecticide (deltamethrin). The WHO prequalifies no DDT products for vector control, and the chemical is banned in Tanzania. Widespread DDT contamination and a legacy of extensive countrywide stockpiles may have selected for this mutation. Continued monitoring is necessary to understand the origin of kdr in An. funestus, and the threat posed to insecticide-based vector control in Africa.

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

BACKGROUND

Afrotropical 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.

METHODS

Host-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.

RESULTS

Nocturnal 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.

CONCLUSIONS

This 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.

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.

Molecular xenomonitoring reveals Anopheles funestus and An. rivulorum as the primary vectors of lymphatic filariasis in coastal Kenya

BACKGROUND

Lymphatic filariasis (LF) is an infectious neglected tropical disease caused by mosquito-borne nematodes such as Wuchereria bancrofti, Brugia malayi, and Brugia timori. Globally, LF affects 51 million people, with approximately 863 million at risk in 47 countries. In Kenya, filariasis is endemic along the entire coastal strip, and more recently, at the Kenya-Ugandan border. The World Health Organization (WHO) recommends mass drug administration to reduce disease transmission and morbidity. Monitoring the effectiveness of such interventions relies on robust surveillance, achieved through microscopic examination of microfilariae in nighttime blood, detection of circulating filarial antigens (CFA), and molecular xenomonitoring. We focused on molecular xenomonitoring along the Kenyan coast due to its noninvasive nature and the opportunity to identify new vectors.

METHODS

In 2022, mosquitoes were collected from Kilifi, Kwale, and Taita-Taveta counties located within the LF endemic region in Kenya. Subsequently, genomic deoxyribonucleic acid (gDNA) was extracted from these mosquitoes for speciation and analysis of Wuchereria bancrofti infection rates. The impact of sociodemographic and household attributes on infection rates was assessed using generalized estimating equations.

RESULTS

A total of 18,121 mosquitoes belonging to Culicinae (63.0%, n = 11,414) and Anophelinae (37.0%, n = 6707) subfamilies were collected. Morphological identification revealed that Anopheline mosquitoes were dominated by An. funestus (45.4%, n = 3045) and An. gambiae (42.8%, n = 2873). Wuchereria bancrofti infection rates were highest in Kilifi (35.4%; 95% CI 28.0-43.3%, n = 57/161) and lowest in Taita Taveta (5.3%; 95% CI 3.3-8.0%, n = 22/412). The major vectors incriminated are An. rivulorum, An. funestus sensu stricto, and An. arabiensis. Mosquitoes of the An. funestus complex were significantly associated with LF transmission (OR 18.0; 95% CI 1.80-180; p = 0.014). Additionally, a higher risk of transmission was observed outdoors (OR 1.74; 95% CI 1.08-2.82; p = 0.024) and in homesteads that owned livestock (OR 2.00; 95% CI 1.09-3.66; p = 0.025).

CONCLUSIONS

In this study, we identified An. funestus s.l. sibling species, An. rivulorum and An. funestus s.s., as the primary vectors of lymphatic filariasis along the Kenyan coast. These findings also highlight that a significant portion of disease transmission potentially occurs outdoors where indoor-based vector control tools, including long-lasting insecticidal nets and indoor residual spray, may not be effective. Therefore, control measures targeting outdoor resting mosquitoes such as zooprophylaxis, larval source management, and attractive sugar baits may have potential for LF transmission reduction.

Bionomics and distribution of malaria vectors in Kisumu city, Western Kenya: Implications for urban malaria transmission

Background

Increasing urbanization in tropical Africa may create new niches for malaria vectors, potentially leading to higher disease transmission rates. Vector control efforts remain largely targeted at ecologically rural bio-complexities with multiple hosts. Understanding mosquito species composition, ecology, host diversity and biting behavior in urban areas is crucial for planning effective control. This study assessed mosquito species diversity, abundance, behavioral patterns, and Plasmodium sporozoite infection rates of Anopheles vectors along an urban-rural transect in Kisumu city, western Kenya.

Methods

Indoor and outdoor host-seeking and resting adult mosquitoes were collected using Centers for Disease Control and Prevention miniature light traps (CDC-LT) and mechanical aspirators (Prokopack) along an urban-rural transect. Females Anopheles mosquitoes collected were identified using morphological taxonomic keys to species level. Specimens belonging to the Anopheles gambiae complex and Anopheles funestus group were further processed using polymerase chain reaction (PCR) to identify members of each complex/group. Subsequently, sporozoite infection rates of the anopheline mosquitoes were determined using a multiplexed real-time quantitative PCR (qPCR) assay.

Result

A total of 3,394 female Anopheles mosquitoes were collected and identified. These comprised of An. gambiae s.l. (68%), An. funestus group (19.8%), An. coustani (7.8%), An. pharoensis (2.6%), An. maculipalipis (1.6%), and An. leesoni(0.2%). All six species were found in urban zone, but only three were found in peri-urban and rural sites. Overall, urban collections accounted for the majority of these collections (55.5%) of mosquitoes collected, followed by those from peri-urban (30%) and rural sites (14.5%). Species distribution across the three ecotypes showed Anopheles arabiensis was the dominant species in urban (84.3%) and peri-urban (89%) sites, while An. gambiae s.s. was predominantly found in the rural zone (60.2%) alongside An. arabiensis (39.7%). Anopheles funestus was the predominant species in peri-urban (98.4%) and rural (85.7%) areas, with An. leesoni accounted for 1.6% and 14.3%, respectively. In urban areas, all samples from the An. funestus group were identified as An. funestus s.s.. Majority (55.5%) of Anopheles mosquitoes were collected indoors, while secondary vectors were primarily caught outdoors. Overall, sporozoite rates were higher outdoors 3.5% compared to indoors 1.45% in rural areas. Specifically, sporozoite infectivity rates for An. funestus, An. gambiae s.s and An. arabiensis collected indoors in the rural zone was 2.5%, 1.4% and 1% respectively. Outdoors in rural areas, An. gambiae had a sporozoite rate of 5.3%, while An. arabiensis had a rate of 2.1%. In peri-urban areas An. gambiae had a sporozoite rate of 2.3%. No sporozoites were detected in samples from urban sites.

Conclusion

The study highlights a shift of diversity of Anopheles species towards urban areas with increased outdoor activity, and significant outdoor malaria transmission in rural and peri-urban areas, emphasizing the need for tools targeting outdoor-biting mosquitoes. The presence of An. funestus in urban settings is of interest and highlights the critical importance of sustained entomological surveillance to inform integrated vector control and prevent future transmission risks.

Insights into malaria vectors-plant interaction in a dryland ecosystem

Improved understanding of mosquito-plant feeding interactions can reveal insights into the ecological dynamics of pathogen transmission. In wild malaria vectors Anopheles gambiae s.l. and An. funestus group surveyed in selected dryland ecosystems of Kenya, we found a low level of plant feeding (2.8%) using biochemical cold anthrone test but uncovered 14-fold (41%) higher rate via DNA barcoding targeting the chloroplast rbcL gene. Plasmodium falciparum positivity was associated with either reduced or increased total sugar levels and varied by mosquito species. Gut analysis revealed the mosquitoes to frequently feed on acacia plants (~ 89%) (mainly Vachellia tortilis) in the family Fabaceae. Chemical analysis revealed 1-octen-3-ol (29.9%) as the dominant mosquito attractant, and the sugars glucose, sucrose, fructose, talose and inositol enriched in the vegetative parts, of acacia plants. Nutritional analysis of An. longipalpis C with high plant feeding rates detected fewer sugars (glucose, talose, fructose) compared to acacia plants. These results demonstrate (i) the sensitivity of DNA barcoding to detect plant feeding in malaria vectors, (ii) Plasmodium infection status affects energetic reserves of wild anopheline vectors and (iii) nutrient content and olfactory cues likely represent potent correlates of acacia preferred as a host plant by diverse malaria vectors. The results have relevance in the development of odor-bait control strategies including attractive targeted sugar-baits.

Entomological effects of attractive targeted sugar bait station deployment in Western Zambia: vector surveillance findings from a two-arm cluster randomized phase III trial

BACKGROUND

Attractive targeted sugar bait (ATSB) stations are a novel tool with potential to complement current approaches to malaria vector control. To assess the public health value of ATSB station deployment in areas of high coverage with standard vector control, a two-arm cluster-randomized controlled trial (cRCT) of Sarabi ATSB® stations (Westham Ltd., Hod-Hasharon, Israel) was conducted in Western Province, Zambia, a high-burden location were Anopheles funestus is the dominant vector. The trial included 70 clusters and was designed to measure the effect of ATSBs on case incidence and infection prevalence over two 7-month deployments. Reported here are results of the vector surveillance component of the study, conducted in a subset of 20 clusters and designed to provide entomological context to guide overall interpretation of trial findings.

METHODS

Each month, 200 paired indoor-outdoor human landing catch (HLC) and 200 paired light trap (LT) collections were conducted to monitor An. funestus parity, abundance, biting rates, sporozoite prevalence, and entomological inoculation rates (EIR).

RESULTS

During the study 20,337 female An. funestus were collected, 11,229 from control and 9,108 from intervention clusters. A subset of 3,131 HLC specimens were assessed for parity: The mean non-parous proportion was 23.0% (95% CI 18.2-28.7%, total n = 1477) in the control and 21.2% (95% CI 18.8-23.9%, total n = 1654) in the intervention arm, an OR = 1.05 (95% CI 0.82-1.34; p = 0.688). A non-significant reduction in LT abundance (RR = 0.65 [95% CI 0.30-1.40, p = 0.267]) was associated with ATSB deployment. HLC rates were highly variable, but model results indicate a similar non-significant trend with a RR = 0.68 (95%CI 0.22-2.00; p = 0.479). There were no effects on sporozoite prevalence or EIR.

CONCLUSIONS

Anopheles funestus parity did not differ across study arms, but ATSB deployment was associated with a non-significant 35% reduction in vector LT density, results that are consistent with the epidemiological impact reported elsewhere. Additional research is needed to better understand how to maximize the potential impact of ATSB approaches in Zambia and other contexts.

TRIAL REGISTRATION NUMBER

This trial was registered with Clinicaltrials.gov (NCT04800055, 16 March 2021).

Livestock keeping, mosquitoes and community viewpoints: a mixed methods assessment of relationships between livestock management, malaria vector biting risk and community perspectives in rural Tanzania

BACKGROUND

Livestock keeping is one of the potential factors related to malaria transmission. To date, the impact of livestock keeping on malaria transmission remains inconclusive, as some studies suggest a zooprophylactic effect while others indicate a zoopotentiation effect. This study assessed the impact of livestock management on malaria transmission risks in rural Tanzania. Additionally, the study explored the knowledge and perceptions of residents about the relationships between livestock keeping and malaria transmission risks in a selected village.

METHODS

In a longitudinal entomological study in Minepa village, South Eastern Tanzania, 40 households were randomly selected (20 with livestock, 20 without). Weekly mosquito collection was performed from January to April 2023. Indoor and outdoor collections used CDC-Light traps, Prokopack aspirators, human-baited double-net traps, and resting buckets. A subsample of mosquitoes was analysed using PCR and ELISA for mosquito species identification and blood meal detection. Livestock's impact on mosquito density was assessed using negative binomial GLMMs. Additionally, in-depth interviews explored community knowledge and perceptions of the relationship between livestock keeping and malaria transmission risks.

RESULTS

A total of 48,677 female Anopheles mosquitoes were collected. Out of these, 89% were Anopheles gambiae sensu lato (s.l.) while other species were Anopheles funestus s.l., Anopheles pharoensis, Anopheles coustani, and Anopheles squamosus. The findings revealed a statistically significant increase in the overall number of An. gambiae s.l. outdoors (RR = 1.181, 95%CI 1.050-1.862, p = 0.043). Also, there was an increase of the mean number of An. funestus s.l. mosquitoes collected in households with livestock indoors (RR = 2.866, 95%CI: 1.471-5.582, p = 0.002) and outdoors (RR = 1.579,95%CI 1.080-2.865, p = 0.023). The human blood index of Anopheles arabiensis mosquitoes from houses with livestock was less than those without livestock (OR = 0.149, 95%CI 0.110-0.178, p < 0.001). The majority of participants in the in-depth interviews reported a perceived high density of mosquitoes in houses with livestock compared to houses without livestock.

CONCLUSION

Despite the potential for zooprophylaxis, this study indicates a higher malaria transmission risk in livestock-keeping communities. It is crucial to prioritize and implement targeted interventions to control vector populations within these communities. Furthermore, it is important to enhance community education and awareness regarding covariates such as livestock that influence malaria transmission.

Association of a rapidly selected 4.3kb transposon-containing structural variation with a P450-based resistance to pyrethroids in the African malaria vector Anopheles funestus

Deciphering the evolutionary forces controlling insecticide resistance in malaria vectors remains a prerequisite to designing molecular tools to detect and assess resistance impact on control tools. Here, we demonstrate that a 4.3kb transposon-containing structural variation is associated with pyrethroid resistance in central/eastern African populations of the malaria vector Anopheles funestus. In this study, we analysed Pooled template sequencing data and direct sequencing to identify an insertion of 4.3kb containing a putative retro-transposon in the intergenic region of two P450s CYP6P5-CYP6P9b in mosquitoes of the malaria vector Anopheles funestus from Uganda. We then designed a PCR assay to track its spread temporally and regionally and decipher its role in insecticide resistance. The insertion originates in or near Uganda in East Africa, where it is fixed and has spread to high frequencies in the Central African nation of Cameroon but is still at low frequency in West Africa and absent in Southern Africa. A marked and rapid selection was observed with the 4.3kb-SV frequency increasing from 3% in 2014 to 98% in 2021 in Cameroon. A strong association was established between this SV and pyrethroid resistance in field populations and is reducing pyrethroid-only nets' efficacy. Genetic crosses and qRT-PCR revealed that this SV enhances the expression of CYP6P9a/b but not CYP6P5. Within this structural variant (SV), we identified putative binding sites for transcription factors associated with the regulation of detoxification genes. An inverse correlation was observed between the 4.3kb SV and malaria parasite infection, indicating that mosquitoes lacking the 4.3kb SV were more frequently infected compared to those possessing it. Our findings highlight the underexplored role and rapid spread of SVs in the evolution of insecticide resistance and provide additional tools for molecular surveillance of insecticide resistance.

LLIN Evaluation in Uganda Project (LLINEUP)-effects of a vector control trial on Plasmodium infection prevalence and genotypic markers of insecticide resistance in Anopheles vectors from 48 districts of Uganda

Pyrethroid bednets treated with the synergist piperonyl butoxide (PBO) offer the possibility of improved vector control in mosquito populations with metabolic resistance. In 2017-2019, we conducted a large-scale, cluster-randomised trial (LLINEUP) to evaluate long-lasting insecticidal nets (LLINs) treated with a pyrethroid insecticide plus PBO (PBO LLINs), as compared to conventional, pyrethroid-only LLINs across 104 health sub-districts (HSDs) in Uganda. In LLINEUP, and similar trials in Tanzania, PBO LLINs were found to provide greater protection against malaria than conventional LLINs, reducing parasitaemia and vector density. In the LLINEUP trial, we conducted cross-sectional household entomological surveys at baseline and then every 6 months for two years, which we use here to investigate longitudinal changes in mosquito infection rate and genetic markers of resistance. Overall, 5395 female Anopheles mosquitoes were collected from 5046 households. The proportion of mosquitoes infected (PCR-positive) with Plasmodium falciparum did not change significantly over time, while infection with non-falciparum malaria decreased in An. gambiae s.s., but not An. funestus. The frequency of genetic markers associated with pyrethroid resistance increased significantly over time, but the rate of change was not different between the two LLIN types. The knock-down resistance (kdr) mutation Vgsc-995S declined over time as Vgsc-995F, the alternative resistance mutation at this codon, increased. Vgsc-995F appears to be spreading into Uganda. Distribution of LLINs in Uganda was previously found to be associated with reductions in parasite prevalence and vector density, but here we show that the proportion of infective mosquitoes remained stable across both PBO and non-PBO LLINs, suggesting that the potential for transmission persisted. The increased frequency of markers of pyrethroid resistance indicates that LLIN distribution favoured the evolution of resistance within local vectors and highlights the potential benefits of resistance management strategies.Trial registration: This study is registered with ISRCTN, ISRCTN17516395. Registered 14 February 2017, http://www.isrctn.com/ISRCTN17516395 .

Entomological survey of sibling species in the Anopheles funestus group in Tanzania confirms the role of Anopheles parensis as a secondary malaria vector

BACKGROUND

Malaria transmission in Tanzania is driven by mosquitoes of the Anopheles gambiae complex and Anopheles funestus group. The latter includes An. funestus s.s., an anthropophilic vector, which is now strongly resistant to public health insecticides, and several sibling species, which remain largely understudied despite their potential as secondary vectors. This paper provides the initial results of a cross-country study of the species composition, distribution and malaria transmission potential of members of the Anopheles funestus group in Tanzania.

METHODS

Mosquitoes were collected inside homes in 12 regions across Tanzania between 2018 and 2022 using Centres for Disease Control and Prevention (CDC) light traps and Prokopack aspirators. Polymerase chain reaction (PCR) assays targeting the noncoding internal transcribed spacer 2 (ITS2) and 18S ribosomal DNA (18S rDNA) were used to identify sibling species in the An. funestus group and presence of Plasmodium infections, respectively. Where DNA fragments failed to amplify during PCR, we sequenced the ITS2 region to identify any polymorphisms.

RESULTS

The following sibling species of the An. funestus group were found across Tanzania: An. funestus s.s. (50.3%), An. parensis (11.4%), An. rivulorum (1.1%), An. leesoni (0.3%). Sequencing of the ITS2 region in the nonamplified samples showed that polymorphisms at the priming sites of standard species-specific primers obstructed PCR amplification, although the ITS2 sequences closely matched those of An. funestus s.s., barring these polymorphisms. Of the 914 samples tested for Plasmodium infections, 11 An. funestus s.s. (1.2%), and 2 An. parensis (0.2%) individuals were confirmed positive for P. falciparum. The highest malaria transmission intensities [entomological inoculation rate (EIR)] contributed by the Funestus group were in the north-western region [108.3 infectious bites/person/year (ib/p/y)] and the south-eastern region (72.2 ib/p/y).

CONCLUSIONS

Whereas An. funestus s.s. is the dominant malaria vector in the Funestus group in Tanzania, this survey confirms the occurrence of Plasmodium-infected An. parensis, an observation previously made in at least two other occasions in the country. The findings indicate the need to better understand the ecology and vectorial capacity of this and other secondary malaria vectors in the region to improve malaria control.

Utility of MALDI-TOF MS for determination of species identity and blood meal sources of primary malaria vectors on the Kenyan coast

Background

Protein analysis using matrix-assisted laser desorption/ionisation time-of-flight mass-spectrometry (MALDI-TOF MS) represents a promising tool for entomological surveillance. In this study we tested the discriminative power of this tool for measuring species and blood meal source of main Afrotropical malaria vectors on the Kenyan coast.

Methods

Mosquito collections were conducted along the coastal region of Kenya. MALDI-TOF MS spectra were obtained from each individual mosquito's cephalothorax as well as the abdomens of blood-engorged mosquitoes. The same mosquitoes were also processed using gold standard tests: polymerase chain reaction (PCR) for species identification and enzyme linked immunosorbent assay (ELISA) for blood meal source identification.

Results

Of the 2,332 mosquitoes subjected to MALDI-TOF MS, 85% (1,971/2,332) were considered for database creation and validation. There was an overall accuracy of 97.5% in the identification of members of the An. gambiae ( An. gambiae, 100%; An. arabiensis, 91.9%; An. merus, 97.5%; and An. quadriannulatus, 90.2%) and An. funestus ( An. funestus, 94.2%; An. rivulorum, 99.4%; and An. leesoni, 94.1%) complexes. Furthermore, MALDI-TOF MS also provided accurate (94.5% accuracy) identification of blood host sources across all mosquito species.

Conclusions

This study provides further evidence of the discriminative power of MALDI-TOF MS to identify sibling species and blood meal source of Afrotropical malaria vectors, further supporting its utility in entomological surveillance. The low cost per sample (<0.2USD) and high throughput nature of the method represents a cost-effective alternative to molecular methods and could enable programs to increase the number of samples analysed and therefore improve the data generated from surveillance activities.

Distribution and insecticide resistance profile of the major malaria vector Anopheles funestus group across the African continent

There has been significant progress in malaria control in the last 2 decades, with a decline in mortality and morbidity. However, these gains are jeopardised by insecticide resistance, which negatively impacts the core interventions, such as insecticide-treated nets (ITN) and indoor residual spraying (IRS). While most malaria control and research efforts are still focused on Anopheles gambiae complex mosquitoes, Anopheles funestus remains an important vector in many countries and, in some cases, contributes to most of the local transmission. As countries move towards malaria elimination, it is important to ensure that all dominant vector species, including An. funestus, an important vector in some countries, are targeted. The objective of this review is to compile and discuss information related to A. funestus populations' resistance to insecticides and the mechanisms involved across Africa, emphasising the sibling species and their resistance profiles in relation to malaria elimination goals. Data on insecticide resistance in An. funestus malaria vectors in Africa were extracted from published studies. Online bibliographic databases, including Google Scholar and PubMed, were used to search for relevant studies. Articles published between 2000 and May 2023 reporting resistance of An. funestus to insecticides and associated mechanisms were included. Those reporting only bionomics were excluded. Spatial variation in species distribution and resistance to insecticides was recorded from 174 articles that met the selection criteria. It was found that An. funestus was increasingly resistant to the four classes of insecticides recommended by the World Health Organisation for malaria vector control; however, this varied by country. Insecticide resistance appears to reduce the effectiveness of vector control methods, particularly IRS and ITN. Biochemical resistance due to detoxification enzymes (P450s and glutathione-S-transferases [GSTs]) in An. funestus was widely recorded. However, An. funestus in Africa remains susceptible to other insecticide classes, such as organophosphates and neonicotinoids. This review highlights the increasing insecticide resistance of An. funestus mosquitoes, which are important malaria vectors in Africa, posing a significant challenge to malaria control efforts. While An. funestus has shown resistance to the recommended insecticide classes, notably pyrethroids and, in some cases, organochlorides and carbamates, it remains susceptible to other classes of insecticides such as organophosphates and neonicotinoids, providing potential alternative options for vector control strategies. The study underscores the need for targeted interventions that consider the population structure and geographical distribution of An. funestus, including its sibling species and their insecticide resistance profiles, to effectively achieve malaria elimination goals.

Discovery of knock-down resistance in the major African malaria vector Anopheles funestus

A major mechanism of insecticide resistance in insect pests is knock-down resistance (kdr) caused by mutations in the voltage-gated sodium channel (Vgsc) gene. Despite being common in most malaria Anopheles vector species, kdr mutations have never been observed in Anopheles funestus, the principal malaria vector in Eastern and Southern Africa. While monitoring 10 populations of An. funestus in Tanzania, we unexpectedly found resistance to DDT, a banned insecticide, in one location. Through whole-genome sequencing of 333 An. funestus samples from these populations, we found 8 novel amino acid substitutions in the Vgsc gene, including the kdr variant, L976F (L1014F in An. gambiae), in tight linkage disequilibrium with another (P1842S). The mutants were found only at high frequency in one region, with a significant decline between 2017 and 2023. Notably, kdr L976F was strongly associated with survivorship to the exposure to DDT insecticide, while no clear association was noted with a pyrethroid insecticide (deltamethrin). Further study is necessary to identify the origin and spread of kdr in An. funestus, and the potential threat to current insecticide-based vector control in Africa.

Genetic markers associated with the widespread insecticide resistance in malaria vector Anopheles funestus populations across Tanzania

BACKGROUND

Anopheles funestus is a leading vector of malaria in most parts of East and Southern Africa, yet its ecology and responses to vector control remain poorly understood compared with other vectors such as Anopheles gambiae and Anopheles arabiensis. This study presents the first large-scale survey of the genetic and phenotypic expression of insecticide resistance in An. funestus populations in Tanzania.

METHODS

We performed insecticide susceptibility bioassays on An. funestus mosquitoes in nine regions with moderate-to-high malaria prevalence in Tanzania, followed by genotyping for resistance-associated mutations (CYP6P9a, CYP6P9b, L119F-GSTe2) and structural variants (SV4.3 kb, SV6.5 kb). Generalized linear models were used to assess relationships between genetic markers and phenotypic resistance. An interactive R Shiny tool was created to visualize the data and support evidence-based interventions.

RESULTS

Pyrethroid resistance was universal but reversible by piperonyl-butoxide (PBO). However, carbamate resistance was observed in only five of the nine districts, and dichloro-diphenyl-trichloroethane (DDT) resistance was found only in the Kilombero valley, south-eastern Tanzania. Conversely, there was universal susceptibility to the organophosphate pirimiphos-methyl in all sites. Genetic markers of resistance had distinct geographical patterns, with CYP6P9a-R and CYP6P9b-R alleles, and the SV6.5 kb structural variant absent or undetectable in the north-west but prevalent in all other sites, while SV4.3 kb was prevalent in the north-western and western regions but absent elsewhere. Emergent L119F-GSTe2, associated with deltamethrin resistance, was detected in heterozygous form in districts bordering Mozambique, Malawi and the Democratic Republic of Congo. The resistance landscape was most complex in western Tanzania, in Tanganyika district, where all five genetic markers were detected. There was a notable south-to-north spread of resistance genes, especially CYP6P9a-R, though this appears to be interrupted, possibly by the Rift Valley.

CONCLUSIONS

This study underscores the need to expand resistance monitoring to include An. funestus alongside other vector species, and to screen for both the genetic and phenotypic signatures of resistance. The findings can be visualized online via an interactive user interface and could inform data-driven decision-making for resistance management and vector control. Since this was the first large-scale survey of resistance in Tanzania's An. funestus, we recommend regular updates with greater geographical and temporal coverage.

The Impact of Climatic Factors on Temporal Mosquito Distribution and Population Dynamics in an Area Targeted for Sterile Insect Technique Pilot Trials

It is widely accepted that climate affects the mosquito life history traits; however, its precise role in determining mosquito distribution and population dynamics is not fully understood. This study aimed to investigate the influence of various climatic factors on the temporal distribution of Anopheles arabiensis populations in Mamfene, South Africa between 2014 and 2019. Time series analysis, wavelet analysis, cross-correlation analysis, and regression model combined with the autoregressive integrated moving average (ARIMA) model were utilized to assess the relationship between climatic factors and An. arabiensis population density. In total 3826 adult An. arabiensis collected was used for the analysis. ARIMA (0, 1, 2) (0, 0, 1)12 models closely described the trends observed in An. arabiensis population density and distribution. The wavelet coherence and time-lagged correlation analysis showed positive correlations between An. arabiensis population density and temperature (r = 0.537 ), humidity (r = 0.495) and rainfall (r = 0.298) whilst wind showed negative correlations (r = -0.466). The regression model showed that temperature (p = 0.00119), rainfall (p = 0.0436), and humidity (p = 0.0441) as significant predictors for forecasting An. arabiensis abundance. The extended ARIMA model (AIC = 102.08) was a better fit for predicting An. arabiensis abundance compared to the basic model. Anopheles arabiensis still remains the predominant malaria vector in the study area and climate variables were found to have varying effects on the distribution and abundance of An. arabiensis. This necessitates other complementary vector control strategies such as the Sterile Insect Technique (SIT) which involves releasing sterile males into the environment to reduce mosquito populations. This requires timely mosquito and climate information to precisely target releases and enhance the effectiveness of the program, consequently reducing the malaria risk.

Rapid assessment of the blood-feeding histories of wild-caught malaria mosquitoes using mid-infrared spectroscopy and machine learning

BACKGROUND

The degree to which Anopheles mosquitoes prefer biting humans over other vertebrate hosts, i.e. the human blood index (HBI), is a crucial parameter for assessing malaria transmission risk. However, existing techniques for identifying mosquito blood meals are demanding in terms of time and effort, involve costly reagents, and are prone to inaccuracies due to factors such as cross-reactivity with other antigens or partially digested blood meals in the mosquito gut. This study demonstrates the first field application of mid-infrared spectroscopy and machine learning (MIRS-ML), to rapidly assess the blood-feeding histories of malaria vectors, with direct comparison to PCR assays.

METHODS AND RESULTS

Female Anopheles funestus mosquitoes (N = 1854) were collected from rural Tanzania and desiccated then scanned with an attenuated total reflectance Fourier-transform Infrared (ATR-FTIR) spectrometer. Blood meals were confirmed by PCR, establishing the 'ground truth' for machine learning algorithms. Logistic regression and multi-layer perceptron classifiers were employed to identify blood meal sources, achieving accuracies of 88%-90%, respectively, as well as HBI estimates aligning well with the PCR-based standard HBI.

CONCLUSIONS

This research provides evidence of MIRS-ML effectiveness in classifying blood meals in wild Anopheles funestus, as a potential complementary surveillance tool in settings where conventional molecular techniques are impractical. The cost-effectiveness, simplicity, and scalability of MIRS-ML, along with its generalizability, outweigh minor gaps in HBI estimation. Since this approach has already been demonstrated for measuring other entomological and parasitological indicators of malaria, the validation in this study broadens its range of use cases, positioning it as an integrated system for estimating pathogen transmission risk and evaluating the impact of interventions.

Rapid classification of epidemiologically relevant age categories of the malaria vector, Anopheles funestus

BACKGROUND

Accurately determining the age and survival probabilities of adult mosquitoes is crucial for understanding parasite transmission, evaluating the effectiveness of control interventions and assessing disease risk in communities. This study was aimed at demonstrating the rapid identification of epidemiologically relevant age categories of Anopheles funestus, a major Afro-tropical malaria vector, through the innovative combination of infrared spectroscopy and machine learning, instead of the cumbersome practice of dissecting mosquito ovaries to estimate age based on parity status.

METHODS

Anopheles funestus larvae were collected in rural south-eastern Tanzania and reared in an insectary. Emerging adult females were sorted by age (1-16 days old) and preserved using silica gel. Polymerase chain reaction (PCR) confirmation was conducted using DNA extracted from mosquito legs to verify the presence of An. funestus and to eliminate undesired mosquitoes. Mid-infrared spectra were obtained by scanning the heads and thoraces of the mosquitoes using an attenuated total reflection-Fourier transform infrared (ATR-FT-IR) spectrometer. The spectra (N = 2084) were divided into two epidemiologically relevant age groups: 1-9 days (young, non-infectious) and 10-16 days (old, potentially infectious). The dimensionality of the spectra was reduced using principal component analysis, and then a set of machine learning and multi-layer perceptron (MLP) models were trained using the spectra to predict the mosquito age categories.

RESULTS

The best-performing model, XGBoost, achieved overall accuracy of 87%, with classification accuracy of 89% for young and 84% for old An. funestus. When the most important spectral features influencing the model performance were selected to train a new model, the overall accuracy increased slightly to 89%. The MLP model, utilizing the significant spectral features, achieved higher classification accuracy of 95% and 94% for the young and old An. funestus, respectively. After dimensionality reduction, the MLP achieved 93% accuracy for both age categories.

CONCLUSIONS

This study shows how machine learning can quickly classify epidemiologically relevant age groups of An. funestus based on their mid-infrared spectra. Having been previously applied to An. gambiae, An. arabiensis and An. coluzzii, this demonstration on An. funestus underscores the potential of this low-cost, reagent-free technique for widespread use on all the major Afro-tropical malaria vectors. Future research should demonstrate how such machine-derived age classifications in field-collected mosquitoes correlate with malaria in human populations.

Comparison of different trapping methods to collect malaria vectors indoors and outdoors in western Kenya

BACKGROUND

Vector surveillance is among the World Health Organization global vector control response (2017-2030) pillars. Human landing catches are a gold standard but difficult to implement and potentially expose collectors to malaria infection. Other methods like light traps, pyrethrum spray catches and aspiration are less expensive and less risky to collectors.

METHODS

Three mosquito sampling methods (UV light traps, CDC light traps and Prokopack aspiration) were evaluated against human landing catches (HLC) in two villages of Rarieda sub-county, Siaya County, Kenya. UV-LTs, CDC-LTs and HLCs were conducted hourly between 17:00 and 07:00. Aspiration was done indoors and outdoors between 07:00 and 11:00 a.m. Analyses of mosquito densities, species abundance and sporozoite infectivity were performed across all sampling methods. Species identification PCR and ELISAs were done for Anopheles gambiae and Anopheles funestus complexes and data analysis was done in R.

RESULTS

Anopheles mosquitoes sampled from 608 trapping efforts were 5,370 constituting 70.3% Anopheles funestus sensu lato (s.l.), 19.7% Anopheles coustani and 7.2% An. gambiae s.l. 93.8% of An. funestus s.l. were An. funestus sensu stricto (s.s.) and 97.8% of An. gambiae s.l. were Anopheles arabiensis. Only An. funestus were sporozoite positive with 3.1% infection prevalence. Indoors, aspiration captured higher An. funestus (mean = 6.74; RR = 8.83, P < 0.001) then UV-LT (mean = 3.70; RR = 3.97, P < 0.001) and CDC-LT (mean = 1.74; RR = 1.89, P = 0.03) compared to HLC. UV-LT and CDC-LT indoors captured averagely 0.18 An. arabiensis RR = 5.75, P = 0.028 and RR = 5.87, P = 0.028 respectively. Outdoors, UV-LT collected significantly higher Anopheles mosquitoes compared to HLC (An. funestus: RR = 5.18, P < 0.001; An. arabiensis: RR = 15.64, P = 0.009; An. coustani: RR = 11.65, P < 0.001). Anopheles funestus hourly biting indoors in UV-LT and CDC-LT indicated different peaks compared to HLC.

CONCLUSIONS

Anopheles funestus remains the predominant mosquito species. More mosquitoes were collected using aspiration, CDC-LTs and UV-LTs indoors and UV-LTs and CD-LTs outdoors compared to HLCs. UV-LTs collected more mosquitoes than CDC-LTs. The varied trends observed at different times of the night suggest that these methods collect mosquitoes with diverse activities and care must be taken when interpreting the results.

Molecular and entomological surveillance of malaria vectors in urban and rural communities of Benguela Province, Angola

BACKGROUND

Malaria is a major public health problem in Angola, with Anopheles gambiae sensu lato (s.l.) and An. funestus s.l. being the primary vectors. This study aimed to clarify the information gaps concerning local Anopheles mosquito populations. Our objectives were to assess their abundance, geographical dispersion, and blood-feeding patterns. We also investigated their insecticide resistance. Molecular methods were used to identify sibling species, determine the origin of blood meals, measure Plasmodium falciparum infection rates, and detect the presence of knockdown resistance (kdr) mutations.

METHODS

Adult mosquitoes were collected indoors using CDC light traps from nine randomly selected households at two sentinel sites with distinct ecological characteristics. The samples were collected from 1 February to 30 June 2022. Anopheles mosquitoes were morphologically identified and subjected to molecular identification. Unfed Anopheles females were tested for the presence of P. falciparum DNA in head and thorax, and engorged females were screened for the source of the blood meals. Additionally, members of An. gambiae complex were genotyped for the presence of the L1014F and L1014S kdr mutations.

RESULTS

In total, 2226 adult mosquitoes were collected, including 733 Anopheles females. Molecular identification revealed the presence of Anopheles coluzzii, An. gambiae senso stricto (s.s.), An. arabiensis, and An. funestus s.s. Notably, there was the first record of An. coluzzii/An. gambiae s.s. hybrid and An. vaneedeni in Benguela Province. Plasmodium falciparum infection rates for An. coluzzii at the urban sentinel site and An. funestus s.s. at the rural site were 23.1% and 5.7%, respectively. The L1014F kdr mutation was discovered in both resistant and susceptible An. coluzzii mosquitoes, while the L1014S mutation was detected in An. gambiae s.s. for the first time in Benguela Province. No kdr mutations were found in An. arabiensis.

CONCLUSIONS

This study provides valuable insights into the molecular characteristics of malaria vectors from the province of Benguela, emphasising the need for continuous surveillance of local Anopheles populations regarding the establishment of both kdr mutations for tailoring vector control interventions.

Early morning anopheline mosquito biting, a potential driver of malaria transmission in Busia County, western Kenya

BACKGROUND

Insecticide-treated nets (ITNs) contributed significantly to the decline in malaria since 2000. Their protective efficacy depends not only on access, use, and net integrity, but also location of people within the home environment and mosquito biting profiles. Anopheline mosquito biting and human location data were integrated to identify potential gaps in protection and better understand malaria transmission dynamics in Busia County, western Kenya.

METHODS

Direct observation of human activities and human landing catches (HLC) were performed hourly between 1700 to 0700 h. Household members were recorded as home or away; and, if at home, as indoors/outdoors, awake/asleep, and under a net or not. Aggregated data was analysed by weighting hourly anopheline biting activity with human location. Standard indicators of human-vector interaction were calculated using a Microsoft Excel template.

RESULTS

There was no significant difference between indoor and outdoor biting for Anopheles gambiae sensu lato (s.l.) (RR = 0.82; 95% CI 0.65-1.03); significantly fewer Anopheles funestus were captured outdoors than indoors (RR = 0.41; 95% CI 0.25-0.66). Biting peaked before dawn and extended into early morning hours when people began to awake and perform routine activities, between 0400-0700 h for An. gambiae and 0300-0700 h for An. funestus. The study population away from home peaked at 1700-1800 h (58%), gradually decreased and remained constant at 10% throughout the night, before rising again to 40% by 0600-0700 h. When accounting for resident location, nearly all bites within the peri-domestic space (defined as inside household structures and surrounding outdoor spaces) occurred indoors for unprotected people (98%). Using an ITN while sleeping was estimated to prevent 79% and 82% of bites for An. gambiae and An. funestus, respectively. For an ITN user, most remaining exposure to bites occurred indoors in the hours before bed and early morning.

CONCLUSION

While use of an ITN was estimated to prevent most vector bites in this context, results suggest gaps in protection, particularly in the early hours of the morning when biting peaks and many people are awake and active. Assessment of additional human exposure points, including outside of the peri-domestic setting, are needed to guide supplementary interventions for transmission reduction.

Overexpression and nonsynonymous mutations of UDP-glycosyltransferases are potentially associated with pyrethroid resistance in Anopheles funestus

UDP-glycosyltransferases (UGTs) enzymes are pivotal in insecticide resistance by transforming hydrophobic substrates into more hydrophilic forms for efficient cell elimination. This study provides the first comprehensive investigation of Anopheles funestus UGT genes, their evolution, and their association with pyrethroid resistance. We employed a genome-wide association study using pooled sequencing (GWAS-PoolSeq) and transcriptomics on pyrethroid-resistant An. funestus, along with deep-targeted sequencing of UGTs in 80 mosquitoes Africa-wide. UGT310B2 was consistently overexpressed Africa-wide and significant gene-wise Fst differentiation was observed between resistant and susceptible populations: UGT301C2 and UGT302A3 in Malawi, and UGT306C2 in Uganda. Additionally, nonsynonymous mutations in UGT genes were identified. Gene-wise Tajima's D density curves provide insights into population structures within populations across these countries, supporting previous observations. These findings have important implications for current An. funestus control strategies facilitating the prediction of cross-resistance to other UGT-metabolised polar insecticides, thereby guiding more effective and targeted insecticide resistance management efforts.

Non-Coding RNAs Potentially Involved in Pyrethroid Resistance of Anopheles funestus Population in Western Kenya

Backgrounds

The resurgence of Anopheles funestus, a dominant vector of human malaria in western Kenya was partly attributed to insecticide resistance. However, evidence on the molecular basis of pyrethroid resistance in western Kenya is limited. Noncoding RNAs (ncRNAs) form a vast class of RNAs that do not code for proteins and are ubiquitous in the insect genome. Here, we demonstrated that multiple ncRNAs could play a potential role in An. funestusresistance to pyrethroid in western Kenya.

Materials and Methods

Anopheles funestus mosquitoes were sampled by aspiration methods in Bungoma, Teso, Siaya, Port Victoria and Kombewa in western Kenya. The F1 progenies were exposed to deltamethrin (0.05%), permethrin (0.75%), DDT (4%) and pirimiphos-methyl (0.25%) following WHO test guidelines. A synergist assay using piperonyl butoxide (PBO) (4%) was conducted to determine cytochrome P450s' role in pyrethroid resistance. RNA-seq was conducted on a combined pool of specimens that were resistant and unexposed, and the results were compared with those of the FANG susceptible strain. This approach aimed to uncover the molecular mechanisms underlying pyrethroid resistance.

Results

Pyrethroid resistance was observed in all the sites with an average mortality rate of 57.6%. Port Victoria had the highest level of resistance to permethrin (MR=53%) and deltamethrin (MR=11%) pyrethroids. Teso had the lowest level of resistance to permethrin (MR=70%) and deltamethrin (MR=87%). Resistance to DDT was observed only in Kombewa (MR=89%) and Port Victoria (MR=85%). A full susceptibility to P-methyl (0.25%) was observed in all the sites. PBO synergist assay revealed high susceptibility (>98%) to the pyrethroids in all the sites except for Port Victoria (MR=96%, n=100). Whole transcriptomic analysis showed that most of the gene families associated with pyrethroid resistance comprised non-coding RNAs (67%), followed by imipenemase (10%), cytochrome P450s (6%), cuticular proteins (5%), olfactory proteins (4%), glutathione S-transferases (3%), UDP-glycosyltransferases (2%), ATP-binding cassettes (2%) and carboxylesterases(1%).

Conclusions

This study unveils the molecular basis of insecticide resistance in An. funestus in western Kenya, highlighting for the first time the potential role of non-coding RNAs in pyrethroid resistance. Targeting non-coding RNAs for intervention development could help in insecticide resistance management.

Evaluation of the DN-Mini (miniaturized double net) trap for sampling host-seeking Anopheles mosquitoes in malaria-endemic villages of southern Tanzania

BACKGROUND

Surveillance of malaria vectors is crucial for assessing the transmission risk and impact of control measures. Human landing catches (HLC) directly estimate the biting rates but raise ethical concerns due to the exposure of volunteers to mosquito-borne pathogens. A common alternative is the CDC-light trap, which is effective for catching host-seeking mosquitoes indoors but not outdoors. New, exposure-free methods are needed for sampling mosquitoes indoors and outdoors in ways that reflect their natural risk profiles. The aim of this study was therefore to evaluate the efficacy of the miniaturized double net trap (DN-Mini) for sampling host-seeking mosquitoes in south-eastern Tanzania, where malaria transmission is dominated by Anopheles funestus.

METHODS

Adult mosquitoes were collected from 222 randomly selected houses across three villages (74 per village) in Ulanga district, south-eastern Tanzania, using the DN-Mini traps, CDC-Light traps, and Prokopack aspirators. First, we compared CDC-light and DN-Mini traps for collecting indoor host-seeking mosquitoes, while Prokopack aspirators were used for indoor-resting mosquitoes. Second, we deployed the DN-Mini and Prokopack aspirators to collect host-seeking and resting mosquitoes indoors and outdoors. Generalized linear mixed models (GLMM) with a negative binomial distribution were used to compare the effectiveness of the traps for catching different mosquito species.

RESULTS

The DN-Mini was 1.53 times more efficient in collecting An. funestus indoors (RR = 1.53, 95% CI: 1.190-1.98) compared to the CDC-Light trap. However, for Anopheles arabiensis, the DN-Mini caught only 0.32 times as many mosquitoes indoors as the CDC-Light traps (RR = 0.32, 95% CI: 0.183-0.567). Both An. funestus and An. arabiensis were found to be more abundant indoors than outdoors when collected using the DN-Mini trap. Similarly, the Prokopack aspirator was greater indoors than outdoors for both An. funestus and An. arabiensis.

CONCLUSION

The DN-Mini outperformed the CDC-light trap in sampling the dominant malaria vector, An. funestus species, but was less effective in capturing An. arabiensis, and for both vector species, the biting risk was greater indoors than outdoors when measured using the DN-Mini trap. These findings highlight the importance of selecting appropriate trapping methods based on mosquito species and behaviors.

Dynamics of malaria vector composition and Plasmodium falciparum infection in mainland Tanzania: 2017-2021 data from the national malaria vector entomological surveillance

BACKGROUND

In 2015, Tanzania National Malaria Control Programme (NMCP) established a longitudinal malaria vector entomological surveillance (MVES). The MVES is aimed at a periodical assessment of malaria vector composition and abundance, feeding and resting behaviours, and Plasmodium falciparum infection in different malaria epidemiological strata to guide the NMCP on the deployment of appropriate malaria vector interventions. This work details the dynamics of malaria vector composition and transmission in different malaria epidemiological strata.

METHODS

The MVES was conducted from 32 sentinel district councils across the country. Mosquitoes were collected by the trained community members and supervised by the NMCP and research institutions. Three consecutive night catches (indoor collection with CDC light trap and indoor/outdoor collection using bucket traps) were conducted monthly in three different households selected randomly from two to three wards within each district council. Collected mosquitoes were sorted and morphologically identified in the field. Thereafter, the samples were sent to the laboratory for molecular characterization using qPCR for species identification and detection of P. falciparum infections (sporozoites). ELISA technique was deployed for blood meal analysis from samples of blood-fed mosquitoes to determine the blood meal indices (BMI).

RESULTS

A total of 63,226 mosquitoes were collected in 32 district councils from January 2017 to December 2021. Out of which, 39,279 (62%), 20,983 (33%) and 2964 (5%) were morphologically identified as Anopheles gambiae sensu lato (s.l.), Anopheles funestus s.l., and as other Anopheles species, respectively. Out of 28,795 laboratory amplified mosquitoes, 13,645 (47%) were confirmed to be Anopheles arabiensis, 9904 (34%) as An. funestus sensu stricto (s.s.), and 5193 (19%) as An. gambiae s.s. The combined average entomological inoculation rates (EIR) were 0.46 (95% CI 0.028-0.928) for An. gambiae s.s., 0.836 (95% CI 0.138-1.559) for An. arabiensis, and 0.58 (95% CI 0.165-0.971) for An. funestus s.s. with variations across different malaria transmission strata. Anopheles funestus s.s. and An. arabiensis were predominant in the Lake and South-Eastern zones, respectively, mostly in high malaria transmission areas. Monthly mosquito densities displayed seasonal patterns, with two peaks following the rainy seasons, varying slightly across species and district councils.

CONCLUSION

Anopheles arabiensis remains the predominant vector species followed by An. funestus s.s. in the country. Therefore, strengthening integrated vector management including larval source management is recommended to address outdoor transmission by An. arabiensis to interrupt transmission particularly where EIR is greater than the required elimination threshold of less than one (< 1) to substantially reduce the prevalence of malaria infection.

Multiple Anopheles species complicate downstream analysis and decision-making in a malaria pre-elimination area in southern Mozambique

BACKGROUND

Different anopheline species (even within a species group/complex) can differ in their feeding and resting behaviours, which impact both malaria transmission patterns as well as the efficacy of vector control interventions. While morphological identification of sampled specimens is an important first step towards understanding species diversity and abundance, misidentification can result in the implementation of less effective vector control measures, and consequently smaller reductions in the number of local malaria cases. Focusing on southern Mozambique, a malaria pre-elimination area where malaria remains persistent, the aims of this preliminary study were to use molecular identification (CO1 and ITS2 barcoding) to (1) validate the results from the morphological identification (with a particular focus on Anopheles pharoensis and Anopheles squamosus), and (2) have a closer look at the Anopheles coustani group (which includes Anopheles tenebrosus and Anopheles ziemanni).

METHODS

Female anopheline mosquitoes (n = 81) were identified morphologically and subsequently sequenced at the ribosomal DNA internal transcribed spacer region 2 (ITS2) and/or cytochrome oxidase subunit 1 (CO1) loci towards species determination.

RESULTS

Out of the 62 specimens that were identified morphologically to species, 4 (6.5%) were misidentified. Regarding the An. coustani group, morphological identification showed that several members are present in southern Mozambique, including An. coustani sensu lato (s.l.), An. ziemanni and An. tenebrosus. However, based on both ITS2 and CO1 sequences, the exact species remains unknown for the latter two members until voucher sequences are available for comparison.

CONCLUSION

The reason(s) for morphological misidentification of anopheline mosquitoes need to be mitigated. This is usually related to both the capacity (i.e. training) of the microscopist to identify anopheline species, and the information provided in the dichotomous identification key. As the An. coustani complex contributes to (residual) malaria transmission in sub-Saharan Africa, it may play a role in the observed persistent malaria in southern Mozambique. A better baseline characterizing of the local anophelines species diversity and behaviours will allow us to improve entomological surveillance strategies, better understand the impact of vector control on each local vector species, and identify new approaches to target those vector species.

Entomological indicators of Plasmodium species transmission in Goma Tsé-Tsé and Madibou districts, in the Republic of Congo

BACKGROUND

Malaria remains a major public health problem in the Republic of Congo, with Plasmodium falciparum being the deadliest species of Plasmodium in humans. Vector transmission of malaria is poorly studied in the country and no previous report compared rural and urban data. This study aimed to determine the Anopheles fauna and the entomological indices of malaria transmission in the rural and urban areas in the south of Brazzaville, and beyond.

METHODS

Indoor household mosquitoes capture using electric aspirator was performed in rural and urban areas during raining and dry seasons in 2021. The identification of Anopheles species was done using binocular magnifier and nested-PCR. TaqMan and nested-PCR were used to detect the Plasmodium species in the head/thorax and abdomens of Anopheles. Some entomological indices including the sporozoite infection rate, the entomological inoculation rate and the man biting rate were estimated.

RESULTS

A total of 699 Anopheles mosquitoes were collected: Anopheles gambiae sensu lato (s.l.) (90.7%), Anopheles funestus s.l. (6.9%), and Anopheles moucheti (2.4%). Three species of An. gambiae s.l. were identified including Anopheles gambiae sensu stricto (78.9%), Anopheles coluzzii (15.4%) and Anopheles arabiensis (5.7%). The overall sporozoite infection rate was 22.3% with a predominance of Plasmodium falciparum, followed by Plasmodium malariae and Plasmodium ovale. Anopheles aggressiveness rate was higher in households from rural area (1.1 bites/night) compared to that from urban area (0.8 ib/p/n). The overall entomological inoculation rate was 0.13 ib/p/n. This index was 0.17 ib/p/n and 0.092 ib/p/n in rural and in urban area, respectively, and was similar during the dry (0.18 ib/p/n) and rainy (0.14 ib/p/n) seasons.

CONCLUSION

These findings highlight that malaria transmission remains high in rural and urban area in the south of Republic of Congo despite the ongoing control efforts, thereby indicating the need for more robust interventions.

Presence of Plasmodium vivax in Anopheles gambiae and absence in other malaria vectors in Cove-Zagnanando-Ouinhi health zone in southern Benin, West Africa

BACKGROUND

Malaria remains a major public health problem in sub-Saharan Africa, particularly in Benin. The present study aims to evaluate the different Plasmodium species transmitted by malaria vectors in the communes of Cove, Zagnanado and Ouinhi, Southern Benin.

METHODS

The study was conducted between December 2021 and October 2022 in 60 villages spread over the three study communes. Adult mosquitoes were collected from four houses in each village using human landing catches (HLCs). After morphological identification, a subsample of Anopheles gambiae, Anopheles funestus and Anopheles nili was analysed by PCR to test for their infection to the different Plasmodium species.

RESULTS

Anopheles gambiae was collected at higher frequency in all the three study communes, representing 93.5% (95% CI 92.9-94) of all collected mosquitoes (n = 10,465). In total, five molecular species were found, An. gambiae sensu stricto (s.s.) and Anopheles coluzzii of the Gambiae complex, An. funestus and Anopheles leesoni of the Funestus group, and An. nili s.s., the sole species of the Nili group. From the five molecular species, four (An. gambiae s.s., An. coluzzii, An. funestus s.s. and An. nili s.s.) were found to be infected. Plasmodium falciparum was the main Plasmodium species in the study area, followed by Plasmodium vivax and Plasmodium ovale. Only An. gambiae s.s. was infected with all three Plasmodium species, while An. coluzzii was infected with two species, P. falciparum and P. vivax.

CONCLUSIONS

Plasmodium falciparum was the only species tested for in malaria vectors in Benin, and remains the only one against which most control tools are directed. It is, therefore, necessary that particular attention be paid to secondary Plasmodium species for an efficient control of the disease. The presence of P. vivax emphasizes the need for an update of case management for malaria.

Anopheles arabiensis continues to be the primary vector of Plasmodium falciparum after decades of malaria control in southwestern Ethiopia

BACKGROUND

Investigating the species distribution and their role in malaria transmission is important as it varies from place to place and is highly needed to design interventions appropriate to the site. The current study aimed to investigate the Anopheles mosquito species distribution and their infection rate in southwestern Ethiopia.

METHODS

The study was conducted in 14 malaria-endemic kebeles (the smallest administrative unit), which were situated in eight different malaria-endemic districts and four zones in southwestern Ethiopia. Ten per cent of households in each village were visited to collect adult mosquitoes using Centers for Disease Control and Prevention (CDC) light traps. The larval and pupal collection was done from breeding sites within the villages, and reared to adults. Female mosquitoes were morphologically identified. The head and thorax of adult Anopheles mosquitoes were tested for circumsporozoite proteins (CSPs) using ELISA. At the same time, legs, wings, and abdomen were used to identify sibling species using PCR targeting the rDNA intergenic spacers region for species typing of the Anopheles funestus group and the internal transcribed spacer 2 region genes for Anopheles gambiae complex.

RESULTS

A total of 1445 Anopheles mosquitoes comprising eight species were collected. Of 813 An. gambiae complex tested by PCR, 785 (97%) were Anopheles arabiensis, and the remaining 28 (3%) were not amplified. There were 133 An. funestus group captured and tested to identify the species, of which 117 (88%) were positive for Anopheles parensis, and 15 (11%) were not amplified. A single specimen (1%) showed a band with a different base pair length from the known An. funestus group species. Sequencing revealed this was Anopheles sergentii. Among 1399 Anopheles tested for CSPs by ELISA, 5 (0.4%) An. arabiensis were positive for Plasmodium falciparum and a single (0.07%) was positive for Plasmodium vivax.

CONCLUSIONS

Anopheles arabiensis continues to play the principal role in malaria transmission despite implementing indoor-based interventions for decades. Sequencing results suggest that An. sergentii was amplified by the An. funestus group primer, producing PCR amplicon size of different length. Therefore, relying solely on amplifying a specific gene of interest in grouping species could be misleading, as different species may share the same gene.