Crimean-Congo haemorrhagic fever outbreak in Northern Senegal in 2022: Prevalence of the virus in livestock and ticks, associated risk factors and epidemiological implications.

OBJECTIVE: Crimean-Congo haemorrhagic fever (CCHF) is a severe zoonotic arboviral disease that occurs widely in Eastern and Western Europe, Asia and Africa. The disease is becoming of growing public health importance in Senegal. However, analysis of tick infestation, CCHF virus (CCHFV) circulation extent and risk factors during ongoing outbreak are scarce. A thorough outbreak investigation was carried out during a CCHF outbreak in Podor (Northern Senegal) in August 2022. METHODS: Ticks and blood samples were collected from animals (cattle, goats and sheep) randomly selected from confirmed CCHF human cases houses, neighbourhoods and surrounding villages. Blood samples were tested for CCHFV antibodies using a commercial enzyme-linked immunosorbent assay (ELISA) test. Tick samples were screened for CCHFV RNA by RT-PCR. RESULTS: Overall, tick infestation rate (TIR) and CCHFV seroprevalence of livestock were 52.12% (95% confidence interval (CI): 45.54%-58.64%) and 43.28% (95% CI: 36.33%-50.44%), respectively. The TIRs were 87.7% in cattle, 57.6% in sheep and 20.0% in goats. These rates were significantly associated with location, host species and tick control (p < 0.001) but not with animal age and sex (p > 0.7). CCHFV seroprevalence was 80.4% (95% CI: 67.57%-89.77%) in cattle, 35.4% (95% CI: 25.00%-47.01%) in sheep and 21.2% (95% CI: 12.11%-33.02%) in goats. Age, sex, location, animal host and presence of ticks were significantly associated to the presence of antibodies. The 950 ticks collected included among other species, Hyalomma impeltatum (48.84%) and H. rufipes (10.21%). Five pools of Hyalomma ssp. were found CCHFV RT-PCR positive. These infected ticks included 0.86% (4/464) of H. impeltatum collected on cattle and sheep and 1.03% (1/97) of H. rufipes collected on a sheep. CONCLUSIONS: To our knowledge, this is the first report on the extend of tick infestation and CCHFV infection in livestock during an outbreak in Senegal. The results highlight the risk of human infections and the importance of strengthening vector, animal and human surveillance as well as tick control measures in this area to prevent CCHF infections in humans.

Emergence of Crimean-Congo Hemorrhagic Fever Virus in Eastern Senegal in 2022.

Crimean-Congo hemorrhagic fever (CCHF), the most widespread tick-borne viral human infection, poses a threat to global health. In this study, clinical samples collected through national surveillance systems were screened for acute CCHF virus (CCHFV) infection using RT-PCR and for exposure using ELISA. For any CCHF-positive sample, livestock and tick samples were also collected in the neighborhood of the confirmed case and tested using ELISA and RT-PCR, respectively. Genome sequencing and phylogenetic analyses were also performed on samples with positive RT-PCR results. In Eastern Senegal, two human cases and one Hyalomma tick positive for CCHF were identified and a seroprevalence in livestock ranging from 9.33% to 45.26% was detected. Phylogenetic analyses revealed that the human strain belonged to genotype I based on the available L segment. However, the tick strain showed a reassortant profile, with the L and M segments belonging to genotype I and the S segment belonging to genotype III. Our data also showed that our strains clustered with strains isolated in different countries, including Mauritania. Therefore, our findings confirmed the high genetic variability inside the CCHF genotypes and their introduction to Senegal from other countries. They also indicate an increasing CCHF threat in Senegal and emphasize the need to reinforce surveillance using a one-health approach.

Rapid On-Site Detection of Arboviruses by a Direct RT-qPCR Assay.

Arthropod-borne diseases currently constitute a source of major health concerns worldwide. They account for about 50% of global infectious diseases and cause nearly 700,000 deaths every year. Their rapid increase and spread constitute a huge challenge for public health, highlighting the need for early detection during epidemics, to curtail the virus spread, and to enhance outbreak management. Here, we compared a standard quantitative polymerase chain reaction (RT-qPCR) and a direct RT-qPCR assay for the detection of Zika (ZIKV), Chikungunya (CHIKV), and Rift Valley Fever (RVFV) viruses from experimentally infected-mosquitoes. The direct RT-qPCR could be completed within 1.5 h and required 1 µL of viral supernatant from homogenized mosquito body pools. Results showed that the direct RT-qPCR can detect 85.71%, 89%, and 100% of CHIKV, RVFV, and ZIKV samples by direct amplifications compared to the standard method. The use of 1:10 diluted supernatant is suggested for CHIKV and RVFV direct RT-qPCR. Despite a slight drop in sensitivity for direct PCR, our technique is more affordable, less time-consuming, and provides a better option for qualitative field diagnosis during outbreak management. It represents an alternative when extraction and purification steps are not possible because of insufficient sample volume or biosecurity issues.

Ornithodoros sonrai Soft Ticks and Associated Bacteria in Senegal.

The soft ticks, Ornithodoros sonrai, are known as vectors of the tick-borne relapsing fever caused by Borrelia spp. and have also been reported to carry other micro-organisms. The objective of this study was to collect and to identify O. sonrai ticks and to investigate the micro-organisms associated with them. In 2019, an investigation of burrows within human dwellings was conducted in 17 villages in the Niakhar area and in 15 villages in the Sine-Saloum area in the Fatick region of Senegal. Ticks collected from the burrows were identified morphologically and by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Micro-organism screening was performed by bacteria-specific qPCR and some identifications were made by standard PCR and gene sequencing. O. sonrai ticks were found in 100% (17/17) of the villages surveyed in the Niakhar area and in 66% (10/15) of the villages in the Sine-Saloum area. A total of 1275 soft tick specimens were collected from small mammal burrows. The ticks collected were morphologically identified as O. sonrai. About 20% (259/1275) of the specimens were also submitted to MALDI-TOF MS for identification. Among the resulting MS profiles, 87% (139/159) and 95% (95/100) were considered good quality specimens, preserved in alcohol and silica gel, respectively. All spectra of good quality were tested against our MALDI-TOF MS arthropod spectra database and identified as O. sonrai species, corroborating the morphological classification. The carriage of four micro-organisms was detected in the ticks with a high prevalence of Bartonella spp., Anaplasmataceae, and Borrelia spp. of 35, 28, and 26%, respectively, and low carriage of Coxiella burnetii (2%). This study highlights the level of tick infestation in domestic burrows, the inventory of pathogens associated with the O. sonrai tick, and the concern about the potential risk of tick involvement in the transmission of these pathogens in Senegal.

Survey of bed bug infestations in homeless shelters in southern France.

Bed bug has become a major public health pest worldwide. Infestation may result in numerous negative health effects. Homeless shelters are one of the most habitats that can be infested with bed bugs, a few studies have focused on bed bug infestations in these settings. We conducted a survey of infestations of bed bugs in a homeless shelter in southern France, using an innovative seven-level scale (0-6) to assess the degree of infestation, MALDI TOF-MS to identify bed bugs, and a biomolecular tool to detect bacteria. Bed bug infestations were documented in 13% (9/68) of investigated rooms. A total of 184 bed bugs were collected and morphologically identified as Cimex lectularius. MALDI TOF-MS analysis allowed us to obtain high-quality MS spectra for all 184 specimens, to correctly identify all specimens, and included 178/184 (97%) Log Score Values higher than 1.8. Among the bacteria tested, Wolbachia sp. DNA was found in 149/184 (81%) of the bed bugs, and one sample was positive for Coxiella burnetii, the agent of Q fever. Our study is the first of its kind that offers new perspectives for increasing public awareness of the conditions in homeless shelters.

Novel Amplicon-Based Sequencing Approach to West Nile Virus.

West Nile virus is a re-emerging arbovirus whose impact on public health is increasingly important as more and more epidemics and epizootics occur, particularly in America and Europe, with evidence of active circulation in Africa. Because birds constitute the main reservoirs, migratory movements allow the diffusion of various lineages in the world. It is therefore crucial to properly control the dispersion of these lineages, especially because some have a greater health impact on public health than others. This work describes the development and validation of a novel whole-genome amplicon-based sequencing approach to West Nile virus. This study was carried out on different strains from lineage 1 and 2 from Senegal and Italy. The presented protocol/approach showed good coverage using samples derived from several vertebrate hosts and may be valuable for West Nile genomic surveillance.

Detection of Crimean-Congo Haemorrhagic Fever Virus from Livestock Ticks in Northern, Central and Southern Senegal in 2021.

Crimean-Congo haemorrhagic fever virus (CCHFV) occurs sporadically in Senegal, with a few human cases each year. This active circulation of CCHFV motivated this study which investigated different localities of Senegal to determine the diversity of tick species, tick infestation rates in livestock and livestock infections with CCHFV. The samples were collected in July 2021 from cattle, sheep and goats in different locations in Senegal. Tick samples were identified and pooled by species and sex for CCHFV detection via RT-PCR. A total of 6135 ticks belonging to 11 species and 4 genera were collected. The genus Hyalomma was the most abundant (54%), followed by Amblyomma (36.54%), Rhipicephalus (8.67%) and Boophilus (0.75%). The prevalence of tick infestation was 92%, 55% and 13% in cattle, sheep and goats, respectively. Crimean-Congo haemorrhagic fever virus (CCHFV) was detected in 54/1956 of the tested pools. The infection rate was higher in ticks collected from sheep (0.42/1000 infected ticks) than those from cattle (0.13/1000), while all ticks collected from goats were negative. This study confirmed the active circulation of CCHFV in ticks in Senegal and highlights their role in the maintenance of CCHFV. It is imperative to take effective measures to control tick infestation in livestock to prevent future CCHFV infections in humans.

Human and Livestock Surveillance Revealed the Circulation of Rift Valley Fever Virus in Agnam, Northern Senegal, 2021.

The mosquito-borne disease caused by the Rift Valley Fever Virus (RVFV) is a viral hemorrhagic fever that affects humans and animals. In 1987, RVFV emerged in Mauritania, which caused the first RVFV outbreak in West Africa. This outbreak was shortly followed by reported cases in humans and livestock in Senegal. Animal trade practices with neighboring Mauritania suggest northern regions of Senegal are at high risk for RVF. In this study, we aim to conduct a molecular and serological survey of RVFV in humans and livestock in Agnam (northeastern Senegal) by RT-PCR (reverse transcription real-time polymerase chain reaction) and ELISA (Enzyme-Linked Immunosorbent Assay), respectively. Of the two hundred fifty-five human sera, one (0.39%) tested RVFV IgM positive, while fifty-three (20.78%) tested positive for RVFV IgG. For animal monitoring, out of 30 sheep recorded and sampled over the study period, 20 (66.67%) showed seroconversion to RVFV IgG antibodies, notably during the rainy season. The presence of antibodies increased significantly with age in both groups (p < 0.05), as the force of RVF infection (FOI), increased by 16.05% per year for humans and by 80.4% per month for livestock sheep. This study supports the usefulness of setting up a One Health survey for RVF management.

Assessment of the Risk of Exotic Zika Virus Strain Transmission by Aedes aegypti and Culex quinquefasciatus from Senegal Compared to a Native Strain.

Zika virus (ZIKV) shows an enigmatic epidemiological profile in Africa. Despite its frequent detection in mosquitoes, few human cases have been reported. This could be due to the low infectious potential or low virulence of African ZIKV lineages. This study sought to assess the susceptibility of A. aegypti and C. quinquefasciatus to ZIKV strains from Senegal, Brazil, and New Caledonia. Vertical transmission was also investigated. Whole bodies, legs/wings and saliva samples were tested for ZIKV by real-time PCR to estimate infection, dissemination and transmission rates as well as the infection rate in the progeny of infected female A. aegypti. For A. aegypti, the Senegalese strain showed at 15 days post-exposure (dpe) a significantly higher infection rate (52.43%) than the Brazilian (10%) and New Caledonian (0%) strains. The Brazilian and Senegalese strains were disseminated but not detected in saliva. No A. aegypti offspring from females infected with Senegalese and Brazilian ZIKV strains tested positive. No infection was recorded for C. quinquefasciatus. We observed the incompetence of Senegalese A. aegypti to transmit ZIKV and the C. quinquefasciatus were completely refractory. The effect of freezing ZIKV had no significant impact on the vector competence of Aedes aegypti from Senegal, and vertical transmission was not reported in this study.

Power optimization of a photovoltaic system with artificial intelligence algorithms over two seasons in tropical area.

Power output from the PV module changes continuously with time depending upon the climatic condition. This changes are most important in tropical area like Senegal due to the variation of the seasons (dry and rainy). Furthermore, different types of maximum power point tracking (MPPT) algorithm are presented in literature in order to get maximum output from the PV system. They can be summarized in two categories: classical and intelligent methods. The classical methods in no uniform weather condition are not efficient and an important loss of energy is showed. However, faced to this problematics like energy loss and no uniform weather conditions an Adaptative methods is used to optimize the PVs energy. In this study, two intelligent controllers based on artificial neural networks (ANN) and Adaptive Neuro Fuzzy Inference System (ANFIS) are proposed to optimize the PVs production in non-uniform weather conditions and compared in order to show the most powerful model. For the ANN, the main challenge is to find the optimal neural in the hidden layer and in the paper, it is obtained using evaluator factor like mean squared error (MSE). These techniques using artificial intelligence (AI) algorithms are used for power optimization of a photovoltaic system are trained and validated with real data from a photovoltaic micro power plant in dry and rainy season installed at polytechnic high school of Dakar. The performances of the controllers to optimize the PVs power are evaluated during the dry and rainy seasons. Simulation results show that the ANFIS MPPT controller is more efficient and robust than ANN in non-uniform weather conditions. They have the ability of generalization and adaption to each meteorological conditions. These bullet summarize the applied methodology•A real electrical characteristics of photovoltaic panel are used for learning and validation of the controllers.•A comparative study of the methods in two different season is done.•ANFIS gives best performance in weather conditions compared to the ANN.

Pathogen Detection in Ornithodoros sonrai Ticks and Invasive House Mice Mus musculus domesticus in Senegal.

Ornithodoros sonrai (O. sonrai) ticks are the only known vectors of Borrelia crocidurae, an agent of tick-borne relapsing fever (TBRF) borreliosis. Rodents serve as principal natural reservoirs for Borrelia. Our research objective was to detect TBRF Borrelia and other zoonotic bacterial infections in ticks and in house mice Mus musculus domesticus, an invasive species currently expanding in rural northern Senegal. Real-time and conventional PCR were utilized for detecting Borrelia and other bacterial taxa. The analyses were performed on 253 specimens of O. sonrai and 150 samples of brain and spleen tissue from rodents. Borrelia crocidurae was found in one O. sonrai tick and 18 Mus musculus domesticus samples, with prevalences of 0.39 percent and 12 percent, respectively, as well as Ehrlichia sp. in one Mus musculus domesticus. Further, we were able to detect the presence of a potentially infectious novel species belonging to the Anaplasmataceae family for the first time in O. sonrai ticks. More attention should be paid to the house mouse and O. sonrai ticks, as they can be potential hosts for novel species of pathogenic bacteria in humans.

Re-Introduction of West Nile Virus Lineage 1 in Senegal from Europe and Subsequent Circulation in Human and Mosquito Populations between 2012 and 2021.

West Nile virus (WNV) is a virus of the Japanese encephalitis antigenic complex and belongs to the family Flaviviridae of the genus flavivirus. The virus can cause infection in humans which in most cases is asymptomatic, however symptomatic cases exist and the disease can be severe causing encephalitis and meningoencephalitis. The virus is maintained in an enzootic cycle involving mosquitoes and birds, humans and other mammals such as horses can be accidental hosts. A mosquito-based arbovirus surveillance system and the sentinel syndromic surveillance network (4S) have been in place since 1988 and 2015 respectively, to better understand the transmission dynamics of arboviruses including WNV in Senegal. Arthropod and human samples have been collected from the field and analysed at Institut Pasteur de Dakar using different methods including RT-PCR, ELISA, plaque reduction neutralization test and viral isolation. RT-PCR positive samples have been analysed by Next Generation Sequencing. From 2012 to 2021, 7912 samples have been analysed and WNV positive cases have been detected, 20 human cases (19 IgM and 1 RT-PCR positive cases) and 41 mosquito pools. Phylogenetic analyzes of the sequences of complete genomes obtained showed the circulation of lineage 1a, with all these recent strains from Senegal identical to each other and very close to strains isolated from horse in France in 2015, Italy and Spain. Our data showed lineage 1a endemicity in Senegal as previously described, with circulation of WNV in humans and mosquitoes. Phylogenetic analyzes carried out with the genome sequences obtained also revealed exchanges of WNV strains between Europe and Senegal which could be possible via migratory birds. The surveillance systems that have enabled the detection of WNV in humans and arthropods should be extended to animals in a one-health approach to better prepare for global health threats.

Multiple genotypes of Crimean-Congo hemorrhagic fever virus detected in ticks during a one health survey in Agnam, Northeastern Senegal.

A Crimean-Congo Hemorrhagic Fever Virus (CCHFV) survey in Agnam (North Senegal) permits the detection of three isolates in ticks. These isolates belong genetically to multiple genotypes (I, II, III) and clustered with strains from Uganda, Sudan, Mauritania, and Senegal. The role of ticks in CCHF emergence and widespread is highlighted.

Crimean-Congo Hemorrhagic Fever Virus Survey in Humans, Ticks, and Livestock in Agnam (Northeastern Senegal) from February 2021 to March 2022.

Crimean-Congo hemorrhagic fever virus (CCHFV) is widespread in Asia, Europe, and Africa. In Senegal, sporadic cases of CCHFV have been reported since 1960. Bordering Mauritania in northeastern Senegal, Agnam is an arid area in the region of Matam where CCHFV is endemic, which harbors a pastoralist community. Given the drought conditions of Agnam, inhabitants are in constant movement with their animals in search of pasture, which brings them into contact with pathogens such as arboviruses. To identify CCHFV in this area, we established a One Health site in order to analyze animal livestock, ticks and human samples collected over a one-year period by qRT-PCR and ELISA. Our analysis showed one (1/364) patient carried anti-CCHFV IgM and thirty-seven carried anti-CCHFV IgG (37/364). In livestock, anti-CCHFV IgG was detected in 13 (38.24%) of 34 sentinel sheep. The risk of CCHFV infection increased significatively with age in humans (p-value = 0.00117) and sheep (p-value = 1.18 × 10-11). Additional risk factors for CCHFV infection in sheep were dry seasons (p-value = 0.004) and time of exposure (p-value = 0.007). Furthermore, we detected a total of three samples with CCHFV RNA within Rhipicephalus evertsi evertsi and Rhipicephalus guilhoni tick species. Our results highlighted the usefulness of a One Health survey of CCHFV in pastoral communities at risk of arboviruses.

Dengue vectors in Africa: A review.

Dengue fever is a mosquito-borne-disease of growing public health importance in Africa. The continuous increase of number and frequency of outbreaks of dengue fever, especially in urban area in Africa underline the need to review the current data available on vectors involved in dengue virus transmission in Africa. Here, we summarized the available data on vectors involved in the transmission of dengue virus in the sylvatic and urban environments, vertical transmission, vector competence studies, and vector control strategies used in Africa. The virus was isolated mainly from Aedes furcifer, Ae. luteocephalus, and Ae. taylori in the sylvatic environment and from Ae. aegypti and Ae. albopictus in the urban areas. Prospective and urgently needed studies on vectors biology, behavior, and alternative control strategies are suggested.

Blood Feeding Patterns of Aedes aegypti Populations in Senegal.

Aedes aegypti plays an important role in the transmission of several arboviruses of medical importance. The availability of information on the blood-feeding preferences of mosquito vectors is a critical step in the understanding of the transmission of human pathogens and implementation of control strategies. In Senegal, no data currently exist on the feeding pattern of Ae. aegypti in urban areas. To fill this gap, Ae. aegypti blood-fed females were collected in five localities by aspiration and using BG Sentinel 2 traps. Collections were carried out monthly between July and November 2019 inside and outside human dwellings. The origin of the blood meal of Ae. aegypti females were identified by an ELISA technique. A total of 1,710 blood-engorged females were examined and showed that Ae. aegypti preferentially fed on human with 78.6% of the identified blood meals. The other blood meals were from animals including dog, cat, horse, cattle, sheep, and rat. This is the first report on the feeding behavior of Ae. aegypti in urban settings in West Africa. It demonstrated that this species is highly anthropophilic.

Morphological, Molecular and MALDI-TOF MS Identification of Bedbugs and Associated Wolbachia Species in Rural Senegal.

Bed bugs are known to carry several microorganisms. The purpose of this study was to assess the prevalence of bed bug infestation in two rural areas of Senegal and determine the species present in the population. A screening was conducted to detect some arthropod associated pathogenic bacteria in bed bugs and to evaluate the prevalence of endosymbiont carriage. One survey took place in 17 villages in Niakhar and two surveys in Dielmo and Ndiop and surroundings area in the same 20 villages. Bed bugs collected were identified morphologically and by MALDI-TOF MS tools. Microorganisms screening was performed by qPCR and confirmed by sequencing. During the survey in the Niakhar region, only one household 1/255 (0.4%) in the village of Ngayokhem was found infested by bed bugs. In a monitoring survey of the surroundings of Dielmo and Ndiop area, high prevalence was found during the two rounds of surveys in 65/314 (21%) in 16/20 villages (January-March) and 93/351 (26%) in 19/20 villages (December). All bed bugs were morphologically identified as the species Cimex hemipterus, of which 285/1,637 (17%) were randomly selected for MALDI-TOF MS analysis and bacteria screening. Among the Bacteria tested only Wolbachia (Alphaproteobacteria, Rickettsiales, Rickettsiaceae) DNA was found in 248/276 (90%) of the bedbugs. We briefly describe a high level of non-generalized bed bug infestation in rural Senegal and the diversity of Wolbachia strains carried by C. hemipterus. This study opens perspectives for raising household awareness of bed bug infestations and possibilities for appropriate control.

Detection of Coxiella burnetii and Borrelia spp. DNA in Cutaneous Samples and in Household Dust in Rural Areas, Senegal.

Q fever and tick-borne borreliosis are two zoonotic diseases rarely diagnosed in Senegalese health facilities, particularly in rural areas. Our study aims to better understand the circulation of Coxiella burnetii and Borrelia spp. DNA on human skin and the domestic environment in rural areas. Cutaneous swabs were taken from febrile patients being treated for borreliosis and/or Q fever, the members of patients' households and control households in the Niakhar area. Dust samples were also collected from 90 households where 54 cases of borreliosis and Q fever were reported as well as from the households of members of control populations in Dielmo, Ndiop, and Niakhar. C. burnetii and Borrelia spp. DNA were detected by quantitative PCR in cutaneous swabs and dust samples targeting spacers IS1111_IS30A and Bor 16S gene. Of 1365 persons tested, 76 were shown to carry C. burnetii, 13 Borrelia spp., and 6 were identified as carrying both C. burnetii and Borrelia spp. The prevalence of Borrelia spp. DNA in households was 16.7% in Dielmo, 6.7% in Ndiop, and 23.3% in all other villages in the Niakhar area, and the presence of C. burnetii in the same localities was 10%, 13.3% and 66.7%, respectively. Furthermore, C. burnetii genotyping identified the presence of Multispacer Sequence Typing group 6. These results revealed for the first time the carriage on the skin of C. burnetii and Borrelia spp. DNA in humans and its wide distribution across households. Our findings suggest that many populations are exposed to these diseases, with frequent contaminating cases of infectious origin arising from the domestic environment.

Yellow Fever Outbreak in Eastern Senegal, 2020-2021.

Yellow fever virus remains a major threat in low resource countries in South America and Africa despite the existence of an effective vaccine. In Senegal and particularly in the eastern part of the country, periodic sylvatic circulation has been demonstrated with varying degrees of impact on populations in perpetual renewal. We report an outbreak that occurred from October 2020 to February 2021 in eastern Senegal, notified and managed through the synergistic effort yellow fever national surveillance implemented by the Senegalese Ministry of Health in collaboration with the World Health Organization, the countrywide 4S network set up by the Ministry of Health, the Institut Pasteur de Dakar, and the surveillance of arboviruses and hemorrhagic fever viruses in human and vector populations implemented since mid 2020 in eastern Senegal. Virological analyses highlighted the implication of sylvatic mosquito species in virus transmission. Genomic analysis showed a close relationship between the circulating strain in eastern Senegal, 2020, and another one from the West African lineage previously detected and sequenced two years ago from an unvaccinated Dutch traveler who visited the Gambia and Senegal before developing signs after returning to Europe. Moreover, genome analysis identified a 6-nucleotide deletion in the variable domain of the 3'UTR with potential impact on the biology of the viral strain that merits further investigations. Integrated surveillance of yellow fever virus but also of other arboviruses of public health interest is crucial in an ecosystem such as eastern Senegal.

Insecticide resistance status and mechanisms in Aedes aegypti populations from Senegal.

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.