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Aedes aegypti is the main epidemic vector of arboviruses in Africa. In Senegal, control activities are mainly limited to mitigation of epidemics, with limited information available for Ae . aegypti populations. A better understanding of the current Ae . aegypti susceptibility status to various insecticides and relevant resistance mechanisms involved is needed for the implementation of effective vector control strategies. The present study focuses on the detection of insecticide resistance and reveals the related mechanisms in Ae . aegypti populations from Senegal. Bioassays were performed on Ae . aegypti adults from nine Senegalese localities (Matam, Louga, Barkedji, Ziguinchor, Mbour, Fatick, Dakar, Kédougou and Touba). Mosquitoes were exposed to four classes of insecticides using the standard WHO protocols. Resistance mechanisms were investigated by genotyping for pyrethroid target site resistance mutations (V1016G, V1016I, F1534C and S989P) and measuring gene expression levels of key detoxification genes ( CYP6BB2 , CYP9J26 , CYP9J28 , CYP9J32 , CYP9M6 , CCEae3a and GSTD4 ). All collected populations were resistant to DDT and carbamates except for the ones in Matam (Northern region). Resistance to permethrin was uniformly detected in mosquitoes from all areas. Except for Barkédji and Touba, all populations were characterized by a susceptibility to 0.75% Permethrin. Susceptibility to type II pyrethroids was detected only in the Southern regions (Kédougou and Ziguinchor). All mosquito populations were susceptible to 5% Malathion, but only Kédougou and Matam mosquitoes were susceptible to 0.8% Malathion. All populations were resistant to 0.05% Pirimiphos-methyl, whereas those from Louga, Mbour and Barkédji, also exhibited resistance to 1% Fenitrothion. None of the known target site pyrethroid resistance mutations was present in the mosquito samples included in the genotyping analysis (performed in > 1500 samples). In contrast, a remarkably high (20-70-fold) overexpression of major detoxification genes was observed, suggesting that insecticide resistance is mostly mediated through metabolic mechanisms. These data provide important evidence to support dengue vector control in Senegal.

Aedes aegypti is the primary vector of dengue, Zika, yellow fever and chikungunya viruses to humans. In Africa, two subspecies, Ae . aegypti aegypti ( Aaa ) and Ae . aegypti formosus ( Aaf ) have been described. Until very recently, it was considered that the two forms were sympatric in East Africa and that only Aaf was present in Central and West Africa. However, recent data suggests that Aaa was also common in Senegal without any clear evidence of genetic differences with Aaf . This study was carried out in different Ae . aegypti populations from Senegal to better clarify their taxonomic status. The larvae, pupae and eggs were collected between July and September 2018 and reared individually to adult stage. For each population, F 1 progeny from eggs laid by a single female F 0 were reared as sibling samples. The number of pale scales on the first abdominal tergite (T 1 ) and the basal part of the second tergite (T 2 ) were counted. Individuals with no pale scale on T 1 were classified as Aaf while those with at least one pale scale on this tergite were classified as Aaa . The morphological variations within families of Aaf were studied across 4 generations. In total, 2400 individuals constituting 240 families were identified, of which 42.5% were heterogeneous (families with both forms). Multivariate statistical analysis of variance including T 1 and T 2 data together showed that populations were significantly different from each other. Statistical analysis of T 1 alone showed a similarity between populations from the southeast while variations were observed within northwest population. The analysis of family composition across generations showed the presence of Aaa and Aaf forms in each generation. The classification of Ae . aegypti into two subspecies is invalid in Senegal. Populations exhibit morphological polymorphism at the intra-family level that could have biological and epidemiological impacts.

Aedes aegypti is the primary vector of arboviruses in Senegal, yet this species is not typically targeted by routine vector control programs. Through entomological surveillance, we investigated over a one-year (2022–2023) the risk of arbovirus transmission in Dakar, Senegal, the spatial distribution of insecticide resistance and the underlying resistance mechanisms. Weekly ovitraps were deployed in 15 localities (10 per locality), and monthly adult mosquito collections were conducted in six localities. Arboviruses were detected in adult Ae. aegypti using Real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and positive sample were sequenced for phylogenetic analysis to determine the genetic diversity. Blood-feeding preferences and resting behaviors were assessed, and WHO tube bioassays evaluated susceptibility to pyrethroids, organophosphates, and carbamates. Molecular screening targeted knockdown resistance ( kdr ) mutations (F1534C, V1016G/I, S989P). Ovitrap positivity peaked between August and October, coinciding with the rainy season. Ae. aegypti was detected in all surveyed localities, and dengue virus (DENV) was found in adult mosquitoes between September and December 2022, confirming active transmission risk. Females predominantly fed on humans and were found resting both indoors and outdoors. All tested populations were resistant to permethrin and bendiocarb, with suspected resistance to malathion. kdr mutations of F1534C (CC, FC), V1016G (VG), S989P (SP, and PP) were detected. These findings demonstrate a substantial entomological risk of arbovirus transmission in Dakar, characterized by high vector density, confirmed DENV infection, and widespread insecticide resistance. In this study, we detected three kdr mutations (F1534C, V1016G, and S989P), while previous studies in Senegal have documented metabolic resistance mechanisms. Together, these resistance mechanisms may compromise the efficacy of vector control strategies. Integrated vector management combining rational insecticide use, source reduction, and innovative control tools is recommended for sustainable Aedes -borne disease control in Senegal.

Background Mosquitoes are well-known vectors for arthropod-borne viruses, yet their role as passive carriers of non-arthropod-borne viruses remains underexplored. Xenosurveillance, a method that utilizes blood-feeding arthropods to sample host and pathogen genetic material, has emerged as a valuable tool in viral ecology. In this study, we investigated the viral landscape of blood-fed mosquitoes from Senegal and report the first detection of Jaagsiekte Sheep Retrovirus (JSRV)-related and Enzootic Nasal Tumor Virus 2 (ENTV-2)-related sequences , alongside endemic arboviruses. Our study aimed to investigate whether mosquitoes can serve as sentinels for detecting both pathogens and host-derived markers in complex ecosystems. Methods Mosquitoes were collected between 2016 and 2019 from three ecologically significant regions in Senegal (Louga, Barkedji, and Kedougou). Blood-fed mosquitoes were pooled and subjected to RNA extraction and metagenomic sequencing using Illumina NextSeq550. Sequencing data were analyzed with CZ-ID and BLAST for viral identification. RT-qPCR assays were designed to validate the presence of JSRV-related sequences, targeting conserved regions of the envelope gene and 3' untranslated region. Phylogenetic analysis was conducted using MAFFT and IQ-TREE to compare the detected sequence with global exogenous and endogenous JSRV references. Results Sequencing revealed a broad viral diversity across mosquito species, including insect-specific viruses, arboviruses (West Nile, Sindbis, Bagaza, Usutu, Barkedji), and two retroviral sequences. A JSRV-related sequence was confirmed in a pool from Barkedji (2019) and clustered phylogenetically with endogenous JSRV . A nearly complete ENTV-2 genome, closely related to pathogenic Chinese strains, was recovered from the same pool . Other viruses grouped within established African lineages, supporting persistent regional circulation. Discussion This study presents the first report of retroviral sequences detected in mosquitoes, alongside the identification of actively circulating arboviruses and insect-specific viruses, highlighting the broader potential of mosquitoes as environmental sentinels. While mosquitoes are not biological vectors for retroviruses, their ability to capture both host-derived retroviral material and pathogenic viral genomes through bloodmeals reinforces the value of xenosurveillance for monitoring livestock–vector–environment interactions. These findings contribute to broader efforts in integrated disease surveillance and underscore the utility of combining metagenomics with molecular diagnostics to detect diverse viral signals in high-risk ecological settings.

Senegal has experienced periodic epidemics of dengue in urban areas with increased incidence in recent years. However, few data are available on the local ecology of the epidemic vectors. In October 2021, a dengue outbreak was reported in northern Senegal to the Institute Pasteur de Dakar. Entomologic investigations then were undertaken to identify the areas at risk of transmission and to identify the vector(s). Adult mosquitoes were collected indoors and outdoors at selected households, while containers with water were inspected for mosquito larvae. All the Aedes aegypti (L.) collected were tested for dengue virus NS1 protein using a rapid diagnostic test (RDT), and positive samples were confirmed by real-time RT–PCR. The qRT–PCR positive samples were subjected to whole genome sequencing using Nanopore technology. The majority of the larvae-positive containers (83.1%) were used for water storage. The Breteau and Container indices exceeded the WHO-recommended thresholds for the risk of dengue virus transmission except at 2 localities. Ae. aegypti, the only reputed dengue vector, was collected resting indoors as well as outdoors and biting during the day and night. The NS1 protein was detected in 22 mosquito pools, including one pool of females emerging from field-collected larvae. All NS1-positive results were confirmed by RT-PCR. Virus serotyping showed that the outbreak was caused by DENV-1. This study demonstrates the need for continuous control of adult and aquatic stages of Ae. aegypti to prevent future dengue epidemics in Senegal. RDTs appear to be a promising tool for dengue diagnostics and surveillance. Graphical Abstract

Aedes aegypti (Linnaeus) is the main vector of most arboviruses in tropical and subtropical urban areas. In West Africa, particularly in Senegal, domestic and wild populations have been described. Both Ae. aegypti aegypti (Aaa) and Ae. aegypti formosus (Aaf) were found in progenies of Ae. aegypti families from several localities of Senegal. However, nothing is known about their resting and trophic behavior, which are key data for vector control. To fill this gap, blood-fed mosquitoes were collected monthly indoors and outdoors with BackPack aspirators and BG-Sentinel 2 traps between July and November 2019 from four urban sites. The enzyme-linked immunosorbent assay technique was used to analyze blood-fed Aaa and Aaf specimens. Both forms were found resting in all investigated places with the highest proportions found in scrap metals (51.7% for Aaa and 44.1% for Aaf) and used tires (19.2% for Aaa and 26.1% for Aaf). Blood-fed Aaf females showed lower occupation of the indoors environment compared to Aaa. Overall, the percentages of single bloodmeals from human were 80.5% (916/1138) for Aaa and 71.1% (263/370) for Aaf. A low frequency of other domestic hosts, including bovine, ovine, and cat were detected for both forms. This study provides the first data on resting and trophic behavior of Aaa and Aaf in Senegal. Both forms showed differences in their resting behavior but fed primarily on human and highlight the risk of arboviruses transmission in urban areas.

Aedes aegypti is the primary vector of dengue, Zika, yellow fever and chikungunya viruses to humans. In Africa, two subspecies, Ae. aegypti aegypti (Aaa) and Ae. aegypti formosus (Aaf) have been described. Until very recently, it was considered that the two forms were sympatric in East Africa and that only Aaf was present in Central and West Africa. However, recent data suggests that Aaa was also common in Senegal without any clear evidence of genetic differences with Aaf. This study was carried out in different Ae. aegypti populations from Senegal to better clarify their taxonomic status. The larvae, pupae and eggs were collected between July and September 2018 and reared individually to adult stage. For each population, F1 progeny from eggs laid by a single female F0 were reared as sibling samples. The number of pale scales on the first abdominal tergite (T1) and the basal part of the second tergite (T2) were counted. Individuals with no pale scale on T1 were classified as Aaf while those with at least one pale scale on this tergite were classified as Aaa. The morphological variations within families of Aaf were studied across 4 generations. In total, 2400 individuals constituting 240 families were identified, of which 42.5% were heterogeneous (families with both forms). Multivariate statistical analysis of variance including T1 and T2 data together showed that populations were significantly different from each other. Statistical analysis of T1 alone showed a similarity between populations from the southeast while variations were observed within northwest population. The analysis of family composition across generations showed the presence of Aaa and Aaf forms in each generation. The classification of Ae. aegypti into two subspecies is invalid in Senegal. Populations exhibit morphological polymorphism at the intra-family level that could have biological and epidemiological impacts.

Background The overlap in the epidemiology of malaria and helminths has been identified as a potential area to exploit for the development of an integrated control strategy that may help to achieve elimination of malaria and helminths. A randomized, controlled, observer-blind trial was conducted to assess the feasibility and safety of combining mass drug administration (MDA) for schistosomiasis and soil transmitted helminths (STH) with seasonal malaria chemoprevention (SMC) among children living in Senegal. Methods Female and male children aged 1–14 years were randomized 1:1:1, to receive Vitamin A and Zinc on Day 0, followed by SMC drugs (sulfadoxine-pyrimethamine and amodiaquine) on Days 1–3 (control group); or praziquantel and Vitamin A on Day 0, followed by SMC drugs on Days 1–3 (treatment group 1); or albendazole and praziquantel on Day 0, followed by SMC drugs on Days 1–3 (treatment group 2). Safety assessment was performed by collecting adverse events from all children for six subsequent days following administration of the study drugs. Pre- and post-intervention, blood samples were collected for determination of haemoglobin concentration, malaria microscopy, and PCR assays. Stool samples were analyzed using Kato-Katz, Merthiolate-iodine-formalin and PCR methods. Urine filtration, PCR and circulating cathodic antigen tests were also performed. Results From 9 to 22 June 2022, 627 children aged 1–14 years were randomized into the three groups described above. Mild, transient vomiting was observed in 12.6% (26/206) of children in treatment group 2, in 10.6% (22/207) in group 1, and in 4.2% (9/214) in the control group (p = 0.005). Pre-intervention, the geometric mean value of Plasmodium falciparum parasite density was highest among children who received albendazole, praziquantel with SMC drugs. Post-intervention, the parasite density was highest among children who received SMC drugs only. Children who received praziquantel and SMC drugs had a lower risk of developing severe anaemia than their counterparts who received SMC drugs alone (OR = 0.81, 95% CI 0.13–5.00, p = 0.63). Conclusions Integration of MDA for helminths with SMC drugs was safe and feasible among Senegalese children. These findings support further evaluation of the integrated control model. Trial registration : The study is registered at Clinical Trial.gov NCT05354258.

Rift Valley fever (RVF) is a re-emerging vector-borne zoonosis with a high public health and veterinary impact. In West Africa, many lineages were previously detected, but since 2020, lineage H from South Africa has been the main cause of the outbreaks. In this study, clinical samples collected through national surveillance were screened for RVF virus (RVFV) acute infection by RT-PCR and IgM ELISA tests. Sequencing, genome mapping and in vitro phenotypic characterization in mammal cells were performed on RT-PCR positive samples in comparison with other epidemic lineages (G and C). Four RVFV human cases were detected in Senegal and the sequence analyses revealed that the strains belonged to lineage H. The in vitro kinetics and genome mapping showed different replication efficiency profiles for the tested RVFV lineages and non-conservative mutations, which were more common to lineage G or specific to lineage H. Our findings showed the re-emergence of lineage H in Senegal in 2022, its high viral replication efficiency in vitro and support the findings that genetic diversity affects viral replication. This study gives new insights into the biological properties of lineage H and calls for deeper studies to better assess its potential to cause a future threat in Senegal.