Aboubacar Sombié

Arboviruses transmitted by Aedes aegypti and Aedes albopictus , including Zika, yellow fever and especially dengue and chikungunya, represent a growing public health concern in Africa. Insecticide‐based strategies remain essential for the prevention and control of arboviral outbreaks. However, insecticide resistance in Ae. aegypti is globally widespread and appears to be rising in sub‐Saharan Africa. Here, we reviewed the distribution and phenotypic and molecular evidence of insecticide resistance in Ae. aegypti across sub‐Saharan Africa and summarized the underlying resistance mechanisms and key knowledge gaps. Bibliographic databases were searched for studies published between January 2010 and December 2023. The review identified 40 studies from 18 of 47 countries in sub‐Saharan Africa. Among adults mosquitoes, resistance to dichlorodiphenyltrichloroethane (DDT) and pyrethroids was reported in multiple studies across West and Central Africa, while resistance to carbamates was also documented in several countries, comparatively fewer studies reported resistance to organophosphates. For larvae 7 of 40 studies assessed susceptibility to temephos, with potential resistance reported in only one study. Molecular investigations identified five kdr mutations including F1534C, V1016I, V410L, V1016G and S989P in 12 countries while metabolic resistance involving cytochrome P450s, carboxylesterases, glutathione S‐transferases and other detoxification enzymes was reported in a smaller number of studies and countries. Overall, the evidence base remains geographically uneven and limited for several insecticide classes and resistance mechanisms. This review highlights important knowledge gaps, including the limited assessment of larvicides, emerging adulticide options, resistance intensity and Aedes‐targeted vector control interventions, and underscores the need for more systematic and standardized insecticide resistance surveillance across sub‐Saharan Africa.

The increasing resistance of mosquito vectors to synthetic insecticides poses a major challenge to vector control and global public health, underscoring the urgent need for sustainable, environmentally safe alternatives. This study evaluated the larvicidal activity of aqueous, ethanolic, methanolic, and hydroethanolic extracts of Calotropis procera (Aiton) W.T.Aiton leaves against Aedes aegypti larvae. Significant variations in activity were observed across extraction solvent, ecological zone, and harvest season, with hydroethanolic extracts—particularly those collected in Kombissiri during the dry season—exhibiting the lowest LC₅₀ values among the tested extracts (LC₅₀ < 1600 ppm), indicating moderate larvicidal activity. Phytochemical profiling by high-performance thin-layer chromatography (HPTLC) revealed the presence of several classes of secondary metabolites, including flavonoids, phenolic compounds, tannins, sterols/triterpenes, saponins, coumarins, alkaloids, and cardenolides. Correlation analysis revealed strong negative correlations between larvicidal activity and the concentrations of flavonoids and phenolic compounds, suggesting that higher levels of these metabolites are associated with increased larvicidal effectiveness and may contribute to the observed bioactivity, although these associations remain correlative and do not establish direct causality. These findings highlight the potential of C. procera as a source of plant-based larvicides and demonstrate the influence of environmental factors on their efficacy. From an environmental health perspective, such plant-derived solutions could provide preliminary data for the future optimization of sustainable vector control strategies, while reducing ecological impact and reliance on synthetic insecticides.

In the absence of commercialized vaccines for most arboviruses, including dengue, chikungunya, and Zika, which are transmitted by Aedes aegypti, the management of vector populations to prevent disease transmission remains the cornerstone of arbovirus control strategies. Larviciding targets the early stages of the mosquito life cycle and subsequently reduces the capacity of adult population to transmit pathogens. Here, we report the susceptibility profile of Ae. aegypti larval populations from two West Africa cities, namely Niamey and Ouagadougou, to organophosphates larvicides. In Niamey, sampling was carried out using ovitraps at two sites, whereas in Ouagadougou, larvae were collected from three different types of larval containers at a single site. Temephos and fenitrothion were tested at six different concentrations each. Mosquito populations from Niamey and Ouagadougou were found susceptible to temephos and fenitrothion, with LD₅₀ < 0.015 mg/L and RR₅₀ < 5. However, Ae. aegypti populations from Ouagadougou showed reduced susceptibility to temephos compared to baseline data from 2016, as indicated by RR₅₀ values. This observation highlights the need for regular surveillance of larval susceptibility, as it may signal the emergence of temephos resistance in Ouagadougou. The acetylcholinesterase (AChE) mutation and the expression levels of metabolic genes Carboxy-/Cholinesterase (CCE) should be characterized to understand the molecular mechanisms underlying the observed phenotype response. Our results provide up-to-date data that could inform the potential deployment of these larvicides for the prevention and control of dengue and chikungunya outbreaks in Ouagadougou and Niamey.

Malaria remains a major public health threat in Burkina Faso, as in most sub-Saharan Africa countries. Malaria control relies mainly on long-lasting insecticide-treated nets (LLINs) and indoor residual spraying. In Burkina Faso, an escalating of insecticide resistance has been observed over the last decades. This study aimed to investigate insecticide resistance and the underlying mechanisms in Anopheles gambiae complex in Ouagadougou. Anopheles gambiae s.l. larvae were collected from gutters and ponds, in Zogona, Tampouy and Tanghin, 3 localities in Ouagadougou from July to October 2018. The larvae were reared in the laboratory to adults stage and susceptibility profile to pyrethroid, carbamate, and organophosphate insecticides was assessed using WHO tube assays. Mosquito species and mutations linked with insecticide resistance, were identified through PCR. More than 95% of the collected An. gambiae s.l. were An. arabiensis. An. arabiensis displayed high resistance to permethrin and deltamethrin, with mortalities below 30%, but was fully susceptible to bendiocarb, fenitrothion, and malathion. A high-frequency of the pyrethroid resistance-associated kdr mutation 1014F (0.81) was recorded, while the frequency of 1014S mutation (0.18) was lower. However, the carbamate and organophosphate-associated Ace-1 119S mutation was not detected. Localities and breeding site type appear to influence pyrethroid resistance in the An. arabiensis population of Ouagadougou. The high resistance to pyrethroids in An. arabiensis of urban Ouagadougou is underpinned, at least in part by high-frequency kdr mutations. This result supports the switch to next-generation LLINs, in well-established pyrethroid resistance zones of Burkina Faso including Ouagadougout

: Recent dengue outbreaks have occurred in Ouagadougou and Bobo-Dioulasso, the two major cities of Burkina Faso. Dengue is a viral disease transmitted primarily by Aedes aegypti, a highly anthropophilic mosquito that thrives in human-transformed environments and breeds predominantly in artificial containers. In 2018, we investigated the resting and blood-feeding habits of Ae. aegypti in urban settings of Ouagadougou. In a 3-month cross-sectional study starting in August 2018, indoors and outdoors resting adult mosquitoes were collected using Prokopack aspirators in three health districts (HD). All mosquitoes were morphologically identified, and DNA was extracted from blood-fed Ae. aegypti females. A multiplex polymerase chain reaction with specific primers was used to identify the origin of the blood meal. A total of 4,256 adult Ae. aegypti mosquitoes, including 1,908 females, were collected. A preference for exophily was recorded in Bogodogo and Nongremassom, although an unexpectedly higher proportion of blood-fed females were found indoors than outdoors. Respectively, 96.09%, 91.03%, and 95.54% of the blood meals successfully analyzed in Baskuy, Bogodogo, and Nongremassom were from a single human host, with the remainder from domestic mammals as single or multiple hosts. Modeling total Ae. aegypti and blood-fed female counts showed that among other predictors, human density, outdoor environment, and house type affect their total densities. Our study revealed an exophilic tendency as well as a pronounced anthropophilic preference of Ae. aegypti adults, critical findings to consider when planning accurate entomological surveillance and effective interventions against Ae. aegypti in urban settings.

Background Since 2013, Burkina Faso has experienced regular dengue outbreaks, especially in Ouagadougou, the capital city, and Bobo-Dioulasso. Insufficient knowledge of the disease and some daily practices and attitudes of the human population may contribute to the proliferation of the vector and subsequently to dengue transmission. The objective of this study was to assess the levels of population knowledge of dengue and its primary vector, Aedes aegypti, and to elucidate the behavioural and environmental factors associated with the proliferation of this species. Methods A cross-sectional Knowledge, Attitude, and Practice (KAP) survey was conducted among 514 individuals, in 514 houses concurrently with a survey on Ae. aegypti larval sites, between September and October 2021 in three health districts (HDs) of Ouagadougou. Compound characteristics, including building materials, annual income, presence of waste, and water storage practices, were also documented. Results A proportion of94.36% of the respondents demonstrated knowledge of dengue, with 50% recognizing primary symptoms like fever and headaches, and 70.52% knowing about its transmission mode. Only 53.51% could identify Aedes larval containers, while 14.04% were familiar with mosquito immature stages. Certain practices were linked to increased dengue vector proliferation or biting, including water storage, open water containers, water-holding waste, and the absence of mosquito screens. The study noted a high number and diversity of potential Aedes larval sites with elevated Stegomyia indices (Container Index >47%, House Index >86%, and Breteau Index >230) across all HDs. Moreover, compound infestation by immature mosquitoes was correlated with tap water presence, resident count, and construction type. Conclusion Despite the dengue outbreaks in the city of Ouagadougou over the past decade and the resulting awareness campaigns, population knowledge of dengue and its vector remains limited. Therefore, there is a critical need to enhance awareness activities through campaigns aimed at changing practices and attitudes, and improving the population’s knowledge regarding the disease and its vector.

The number of dengue cases worldwide has increased ten-fold over the past decade as Aedes aegypti , the primary vector of this disease, thrives and expands its distribution, revealing limitations to current control methods. To better understand how Ae. aegypti evolved from a forest dwelling, generalist species to a highly anthropophilic urban species and the impact of contemporary gene flow on the future of dengue control, we sequenced 1,206 genomes from mosquitoes collected at 74 locations around the globe. Here we show that after evolving a preference for humans in the Sahel region of West Africa, the origin of the fully domesticated, anthropophilic subspecies Ae. aegypti aegypti ( Aaa ) occurred in the Americas during the Atlantic Slave Trade era and was followed by its explosive expansion around the globe. In recent decades, Aaa has invaded coastal Africa, the ancestral home range, introducing insecticide resistance mutations and an affinity for human hosts. Evidence of back-to-Africa migration is found in regions with recent dengue outbreaks, raising concern that global movement of Aaa could increase transmission risk of arboviruses including dengue in urban Africa. These data provide a platform to further study this important mosquito vector species and underscore developing complexity in the fight to limit the spread of dengue, Zika, and chikungunya diseases.

Background: Ae. aegypti is the vector of important μ arboviruses, including dengue, Zika, chikungunya and yellow fever. Despite not being specifically targeted by insecticide-based control programs in West Africa, resistance to insecticides in Ae. aegypti has been reported in countries within this region. In this study, we investigated the status and mechanisms of Ae. aegypti resistance in Niamey, the capital of Niger. This research aims to provide baseline data necessary for arbovirus outbreak prevention and preparedness in the country. Methods: Ovitraps were used to collect Ae. aegypti eggs, which were subsequently hatched in the insectary for bioassay tests. The hatched larvae were then reared to 3–5-day-old adults for WHO tube and CDC bottle bioassays, including synergist tests. The kdr mutations F1534C, V1016I, and V410L were genotyped using allele-specific PCR and TaqMan qPCR methods. Results: Ae. aegypti from Niamey exhibited moderate resistance to pyrethroids but susceptibility to organophosphates and carbamates. The kdr mutations, F1534C, V1016I and V410L were detected with the resistant tri-locus haplotype 1534C+1016L+410L associated with both permethrin and deltamethrin resistance. Whereas the homozygote tri-locus resistant genotype 1534CC+1016LL+410LL was linked only to permethrin resistance. The involvement of oxidase and esterase enzymes in resistance mechanisms was suggested by partial restoration of mosquitoes’ susceptibility to pyrethroids in synergist bioassays. Conclusion: This study is the first report of Ae. aegypti resistance to pyrethroid insecticides in Niamey. The resistance is underpinned by target site mutations and potentially involves metabolic enzymes. The observed resistance to pyrethroids coupled with susceptibility to other insecticides, provides data to support evidence-based decision-making for Ae. aegypti control in Niger.

Background: Resistance to insecticides is spreading among populations of Aedes aegypti , the primary vector of important human arboviruses. The escalating insecticide resistance poses a significant threat to dengue vector control, with an expanding number of countries affected by the disease. To gain a deeper insight into the evolution of insecticide resistance, it is essential to have longitudinal surveillance results, which are currently lacking, particularly from African Ae. aegypti populations. Here we report on three-years of surveillance of Ae. aegypti susceptibility to insecticide resistance phenotypes and associated kdr mutations in Burkina Faso, a country with regular dengue outbreaks. Methods: Ae. aegypti susceptibility to insecticides and the V410L, V1016I, and F1534C kdr target site mutations linked to pyrethroid insecticide resistance were monitored in Ouagadougou from 2016 to 2018. Larvae were collected from artificial containers at two sites and reared to adulthood in an insectary. Bioassays were conducted on female adults, alongside with a laboratory-susceptible strain, following standard WHO protocols. Allele-specific PCR genotyping assays were utilized to identify the V410L, V1016I, and F1534C kdr pyrethroid target site mutations. Results: Bioassays revealed a high level of resistance to permethrin and deltamethrin that progressively increased over the three-year period in both localities. The 1534C mutation was nearly fixed throughout the three years at each locality, and while the closely related 410L and 1016I mutations did not vary between localities, their frequency notably increased from 2016 to 2018. Interestingly, Ae. aegypti populations in both areas remained susceptible to bendiocarb, fenitrothion, and malathion. Modeling the mortality data further confirmed the escalating resistance trend over the years and emphasized the significant role played by the three kdr mutations in conferring resistance to pyrethroids. Conclusion: Mortality rates indicate that Ae. aegypti populations from Ouagadougou are becoming increasingly resistant to pyrethroid insecticides, likely due to an increase in the frequencies of the 410L and 1016I kdr mutations . Organophosphate insecticides are likely to be better alternative options for control.

Background: Since 2000, Burkina Faso has experienced regular dengue cases and outbreaks, making dengue an increasingly important health concern for the country. Previous studies in Burkina Faso reported that resistance of Aedes aegypti to pyrethroid insecticides was associated with the F1534C and V1016I kdr mutations. The current study reports high resistance of Ae. aegypti populations to pyrethroid insecticides, likely supported by mutations in the voltage-gated sodium channel, here evidenced by genotyping the kdr SNPs V410L, V1016I and F1534C. We also describe a new multiplex PCR-based diagnostic of F1534C and V1016I kdr SNPs. Methods: Larvae of Ae. aegypti were collected from three health districts of Ouagadougou in 2018. The resistance status of Ae. aegypti to permethrin (15 μg/ml) and deltamethrin (10 μg/ml) was tested using bottles and to malathion (5%) using WHO tube tests. All bioassays used 1-h exposure and mortality recorded 24 h post-exposure. Bioassay results were interpreted according to WHO thresholds for resistance diagnosis. The kdr mutations were screened using AS-PCR and TaqMan methods in exposed and non-exposed Aedes mosquitoes. Results: Females from all health districts were resistant to permethrin and deltamethrin (< 20% mortality) but were fully susceptible to 5% malathion. The F1534C and V1016I kdr mutations were successfully detected using a newly developed multiplex PCR in perfect agreement with TaqMan method. The 1534C/1016I/410L haplotype was correlated with permethrin resistance but not with deltamethrin resistance; however, the test power was limited by a low frequency of dead individuals in deltamethrin exposure. Conclusions: Resistance to pyrethroid insecticides is associated with kdr mutant haplotypes, while the absence of substantial resistance to malathion suggests that it remains a viable option for dengue vector control in Ouagadougou.