Biology subjects

Zahouli, J. Z. B.

Publications and source records attributed to Zahouli, J. Z. B..

6 recordsLinked to original sources

bioRxiv2026

Multi-site phenotypic characterisation of Kisumu colonies for comparison of insecticide susceptibility between testing centres

Testing of insecticides and insecticide-based vector control tools relies on the use of bioassays whereby insects are exposed and mortality, or another relevant entomological endpoint, is measured. To be able to compare results between products and across time and space standard laboratory strains are used. Insecticide-susceptible strains are often used as comparators in studies involving insecticide-resistant populations. Kisumu is a long-established, widely-used insecticide-susceptible strain of Anopheles gambiae. In this study, 16 facilities across different countries exposed their Kisumu colonies aged 3-5 days to four insecticides (permethrin, alpha-cypermethrin, DDT and pirimiphos-methyl) at a range of concentrations in WHO tube assays to assess susceptibility. Insecticide-treated filter papers were made at the Liverpool School of Tropical Medicine and sent to testing centres, along with a standard protocol and testing conditions requirements, to standardise testing as much as possible. A first observation was that DDT results were affected by the use of Risella oil, the WHO-recommended carrier oil but immiscible in acetone, leading to uneven coating of papers and increased variability in bioassay results (40x variance between colonies). Bioassay data generated by the testing facilities suggest a wide range of susceptibility to different insecticides between colonies of Kisumu: LC50 values between colonies differed, though not significantly, by up to 4x for permethrin, 6x for pirimiphos-methyl, and 15x for alpha-cypermethrin. Some colonies are classified as insecticide resistant based on the WHO definition of <98% mortality on exposure to a discriminating concentration. The assumption that Kisumu is a standard susceptible strain, consistent between facilities is challenged, which has implications when comparing results between studies. We propose genotypic analysis of the colonies to identify signs of resistance markers indicative of contamination from resistant strains or wild mosquitoes, and generation of guidance to support the maintenance and monitoring of susceptible mosquito strains.

zoology↗

bioRxiv2025

Morphological and genetic heterogeneity in Aedes aegypti (Diptera: Culicidae) populations across diverse landscapes in West Africa

Native to sub-Saharan Africa, Aedes aegypti has spread across the globe and is now one of the most significant vectors of arboviruses worldwide. However, data on the ranges of its populations remain sparse, and the genetic variability and ecological adaptability in West Africa are still poorly understood. In this study, we characterized the morphological and genetic diversity of Ae. aegypti across four landscape types (urban, peri-urban, rural, and sylvatic sites) in three West African countries (Burkina Faso, Cote dIvoire, and Ghana). Ae. aegypti exhibited significant variation in abdominal scaling patterns across countries and landscape types, with the sylvatic and urban populations in Burkina Faso displaying the highest proportions of white scales (>50% white scales), while black scales predominated among those from Cote dIvoire and Ghana (>80% black scales). Wing shape displayed limited differentiation between the countries, landscape types, and genetic clusters. Bayesian analysis indicated high gene flow among populations, with notable outliers observed in sylvatic sites from Burkina Faso and admixture patterns suggesting possible human-mediated dispersal. Additionally, two major mitochondrial lineages, clades A and B, were identified. Most samples were categorized under clade B, showing no evidence of clustering by country or landscape type. In contrast, clade A comprised primarily sylvatic specimens from Burkina Faso and a single urban individual from Cote dIvoire. These findings highlight the complex interplay of genetic, environmental, and ecological factors shaping the variations in Ae. aegypti populations in West Africa. They provide insights into the phenotypic and genetic diversity of Ae. aegypti, offering valuable implications for understanding arbovirus transmission dynamics and formulating targeted interventions against arboviral diseases.

ecology↗

bioRxiv2025

Mosquito diversity and arbovirus circulation at the Taï National Park, western Cote d'Ivoire

Understanding the ecological and virological dynamics of mosquito populations across different landscapes is essential for predicting and mitigating the risk of arbovirus spillover. From December 2021 to September 2022, we conducted an entomological and molecular survey across sylvatic, transition, and urban zones in the Tai region of western Cote dIvoire. We collected 4,414 mosquitoes, representing 29 taxa, and grouped them into 1,553 pools of the same taxa for virus detection and identification. While Eretmapoditis sp. were dominant across all zones, their species composition varied between the zones, with Er. fraseri being most abundant in the sylvatic and urban zones. In the transition zone Er. quinquevittatus was the dominant species. Abundance of other species also varied across zones. Aedes aegypti and Anopheles sp. were most frequent in the urban zone with An. gambiae s.l. and An. paludis being the most common ones. Molecular screening revealed flavivirus RNA being present in multiple pools, with the highest detection rates in the transition zone. We were able to assemble three flavivirus contigs, including Cimo flaviviruses II and VIII, known as insect-specific flaviviruses that can influence vector competence. Notably, Anopheles sp. had the highest estimated infection rates in the sylvatic and transition zones, suggesting a potential role in arbovirus ecology. Our findings suggest that Eretmapodites sp., particularly Er. fraseri, may serve as key bridge vectors due to their widespread presence, mammalian feeding behaviour and potential virus competence. The transition zone emerged as a hotspot for arbovirus diversity and vector-host interactions. This study provides the first comprehensive ecological and molecular characterization of mosquito communities in the Tai region since more than twenty years and underscores the importance of longitudinal and habitat-specific surveillance for anticipating spillover risks. Author summaryMosquitoes are important to study because they can carry viruses that spread to humans and animals. These viruses, known as arboviruses, often come from wildlife and can spill over into people, especially when natural and human environments overlap. From late 2021 to 2022, we collected and studied mosquitoes in western Cote dIvoire, across forest, village-forest edges, and towns. We wanted to understand which mosquito species were present, how their populations varied across different landscapes, and whether they carried any viruses. We found that one group of mosquitoes, called Eretmapodites, was common in all areas, with different species dominating in different zones. We also found that some mosquito groups, including Anopheles, carried viruses that could potentially affect humans or influence how diseases spread. The area between forest and town, the transition zone, showed the greatest variety of viruses and mosquitoes. Our work helps show how changes in land use and mosquito ecology can affect the risk of disease outbreaks. By understanding where and when mosquitoes are most likely to carry viruses, we can improve surveillance and better prepare for future disease emergence. This is especially important in regions where people and wildlife live close together.

ecology↗

bioRxiv2025

Patterns of Aedes aegypti immature ecology and arboviral epidemic risks in peri-urban and intra-urban villages of Cocody-Bingerville, Cote d'Ivoire: insights from a dengue outbreak

BackgroundIn Cote dIvoire, Aedes vector studies and arboviral outbreak responses have mostly focused on urbanized neighborhoods including intra-urban villages, but have often neglected peripheral villages. We assessed and compared Aedes aegypti population dynamics and dengue (DEN) and yellow fever (YF) epidemic risks among peri-urban and intra-urban villages during the 2023-2024 DEN outbreaks in Cocody-Bingerville, southern Cote dIvoire. MethodsFrom August 2023 to July 2024, we sampled Aedes eggs, larvae and pupae in the domestic and peridomestic ecozones of three peri-urban and three intra-urban villages. We compared Ae. aegypti larval infestation, container productivity, Stegomyia indices (house index: HI, container index: CI, and Breteau index: BI) and pupal indices (pupae per house index: PHI, pupae per container index: PCI, and pupae per person index: PPI) between the study villages. ResultsAedes aegypti widely dominated Aedes fauna in both peri-urban (98.1%) and intra-urban (99.8%) villages. Immatures were sampled from seven container types. However, the most productive containers were small containers, tires and medium containers which produced 81.8% of all the pupae in the peri-urban villages, and tires and small containers yielding 83.2% in the intra-urban villages. These key containers produced substantially more pupae in the domestic ecozones (70.9%) in the peri-urban villages, but equitably between the domestic (48.8%) and peridomestic (51.2%) ecozones in the intra-urban villages. In each study village, they yielded around 90% and 80% of pupae during the short dry and long rainy seasons, respectively. CI, HI and BI were comparable between the peri-urban (29.9%, 35.9% and 41.4) and intra-urban (36.7%, 48.0% and 56.2) villages, and surpassed the World Health Organization (WHO) DEN and YF epidemic thresholds. PCI (1.26 vs. 3.38 pupae/container) and PHI (1.75 vs. 5.18 pupae/house) were lower in the peri-urban than in the intra-urban villages, while PPI (0.54 vs. 1.25 pupae/person) was similar between the villages. Unlike temperature and relative humidity, all indices were strongly associated with rainfall in all the study villages. ConclusionIn Cocody-Bingerville, all sampled peri-urban and intra-urban villages exhibited high densities of Ae. aegypti immatures and habitats. Although larval habitats were diverse, a limited number of container types accounted for over 80% of pupal production. Stegomyia indices remained consistently elevated, exceeding WHO epidemic thresholds for DEN and YF across all study villages, potentially contributing to ongoing DEN outbreaks. Therefore, vector surveillance and outbreak responses should be extended to peri-urban villages, as they could act as arbovirus re-introduction sources. Community-based interventions targeting the identified key containers could help control the outbreaks. This study provides a baseline for strategically reducing human exposure to arboviruses in the study villages.

ecology↗

bioRxiv2025

Assessing the oviposition and larval ecologies of mosquitoes and Stegomyia indices along an urban-rural gradient during ongoing dengue outbreaks in the arboviral hotspots of Cocody-Bingerville, southeastern Cote d'Ivoire

BackgroundCote dIvoire (West Africa) has recurrently faced multiple outbreaks of Aedes mosquito-transmitted arboviral diseases (e.g., dengue (DEN) and yellow fever (YF)), mainly in the health district of Cocody-Bingerville subjected to rapid urbanization. Thus, this study assessed the ecology of mosquito immatures and Stegomyia indices along an urban-rural gradient during ongoing dengue outbreaks within arboviral hotspots in Cocody-Bingerville. MethodsBetween August 2023 and July 2024, we collected mosquito eggs and larvae in urban, suburban and rural areas of Cocody-Bingerville using standard ovitraps and larval surveys. Collections were done in the domestic and peridomestic ecozones, and during rainy and dry seasons. Species composition, oviposition indices (ovitrap positive index (OPI), mean egg counts per ovitrap (MEO) and egg density index (EDI)) and Stegomyia indices (house index (HI), container index (CI) and Breteau index (BI)) were compared across the study areas, ecozones and seasons, and with the World Health Organization (WHO) DEN and YF epidemic thresholds. ResultsOverall, all the study areas were highly infested with diversified mosquito species, with the highest Stegomyia risk indices recorded in the urban areas. We identified (individuals: species) in the all study (70,550: 15), urban (32,331: 10), suburban (19,768: 14) and rural (18,451: 15) areas. Mosquitoes were mostly abundant in the domestic ecozones and rainy seasons. Larvae bred mainly in tires in the urban and suburban, and small containers in the rural areas. Wild Aedes species (Aedes dendrophilus, Aedes lilii, Aedes fraseri, Aedes luteocephalus, Aedes metallicus and Aedes vittatus) were mostly restricted in the suburban and rural areas, as well as mosquito predatory larvae (Lutzia tigripes, Toxorhynchites and Eretmapodites). However, Aedes aegypti spread and dominated throughout, showing highest proportions in the urban (90.2%), followed by the suburban (68.6%) and rural (68.5%) areas. OPI, MEO (egg/ovitrap/week) and EDI (egg/ovitrap/week) values were higher in the urban areas (53.0%, 8.7 and 16.4) than in the suburban (43.1%, 5.56 and 12.9) and rural (33.7%, 4.4 and 13.0) areas, respectively, and correlated with Stegomyia indices. HI, CI and BI were higher in the urban (48.0%, 40.4% and 61.8) compared with the suburban (37.8%, 32.0% and 43.3) and rural (34.5%, 28.87% and 39.8) areas. Stegomyia indices corresponded to the WHO-density scales of 6-8 in the urban and 5-7 in the suburban and rural areas. Stegomyia indices were all above the WHO epidemic thresholds: YF risk was high the urban and moderate in the suburban and rural areas, while people were permanently exposed to high risk of DEN outbreaks in all the areas. Conclusions/significanceIn Cocody-Bingerville, urbanization shifts mosquito biodiversity, with restriction of wild Aedes and predatory species in the rural and suburban areas and dominance of Ae. aegypti in the urban areas. Stegomyia indices exceeded the WHO DEN and YF epidemic thresholds in all the areas, with highest risks in the urban areas. This could explain the current DEN outbreaks in urban Cocody-Bingerville. Our study provides a baseline for raising local community awareness and guiding appropriate preventive actions, including managing identified larval habitats to contain ongoing dengue outbreaks in Cote dIvoire. Author summaryCote dIvoire has experienced several epidemics of dengue and yellow fever transmitted by Aedes mosquitoes. Over 80-90% of dengue and yellow fever cases were reported in the urban areas of the health district of Cocody-Bingerville, southeastern Cote dIvoire. The increase in the frequency, magnitude and burden of these outbreaks has paralleled to the fast and uncontrolled urbanization. However, data are still lacking on how urbanization influences the ecology of the local mosquito vectors and the risks of transmission of dengue and yellow fever, thus compromising adequate planning of preventive actions. Therefore, we assessed the mosquito species composition and larval breeding sites, and Stegomyia indices in urban, suburban and rural areas within the disease hotspots during ongoing dengue outbreaks in the Cocody-Bingerville. Our results showed that mosquito species diversity altered considerably from urban to rural areas, leading to a dominance of the main vector Aedes aegypti in all the study areas. Moreover, Aedes aegypti showed the highest proportions in the urban areas that contained more larval breeding sites (e.g., tires and small containers). Stegomyia indices were very high and above the World Health Organization (WHO) epidemic thresholds, suggesting that people were exposed to high dengue risks and moderate yellow fever risks in all the study areas, but were more exposed to both diseases in the urban areas. This could explain the recurrent and present dengue outbreaks in urban Cocody-Bingerville. A community-based management of identified larval habitats might help to control the ongoing dengue outbreaks in Cocody-Bingerville, and more widely in similar settings.

ecology↗

bioRxiv2022

Semi-field evaluation of the space spray efficacy of Fludora Co-Max EW against wild insecticide-resistant Aedes aegypti and Culex quinquefasciatus mosquito populations from Abidjan, Cote d'Ivoire

BackgroundSpace spraying of insecticides is still an important mean of controlling Aedes and Culex mosquitoes and arboviral diseases. This study evaluated the space spray efficacy of Fludora Co-Max EW (a combination of flupyradifurone and transfluthrin, with Film Forming Aqueous Spray Technology (FFAST)) against wild, insecticide-resistant Aedes aegypti and Culex quinquefasciatus populations from Abidjan, Cote dIvoire, against K-Othrine EC (deltamethrin-only product), through small-scale field trials. MethodologyWild Ae. aegypti and Cx. quinquefasciatus mosquito larvae were collected in Abidjan, Cote dIvoire from August to December 2020. Mosquito larvae were reared until adult stage. Emerged adult females were tested against Fludora Co-Max EW and K-Othrine EC using ultra-low volume cold fogging (ULV) and thermal fogging (TF) both outdoors and indoors in Agboville, Cote dIvoire. Cages containing 20 mosquitoes each were placed at 10, 25, 50, 75 and 100 m from the spraying line for outdoor spraying, and at ceiling, mid-height and floor levels for indoor house spraying. Knockdown and mortality were recorded at each checkpoint and compared by treatments. Principal findingsOverall, Fludora Co-Max EW induced significantly higher knockdown and mortality effects in the wild insecticide-resistant Ae. aegypti and Cx. quinquefasciatus compared with K-Othrine EC. With both species, Fludora Co-Max EW mortality rates were above 80% (up to 100%) for outdoor ULV spray at each distance checkpoint (i.e. 10 to 100 m), and 100% for indoor ULV and TF sprays at all level checkpoints (i.e. ceiling, mid-height and floor). K-Othrine EC induced high mortality indoors (97.9-100%), whereas outdoor mortality rapidly declined in Ae. aegypti from 96.7% to 36.7% with ULV, and 85.0% to 38.3% with TF, from 10 to 100 m. For outdoor Fludora Co-Max EW spray, ULV showed both higher knockdown and killing performance Ae. aegypti and Cx. quinquefasciatus compared with TF. Fludora Co-Max EW performed better against Cx. quinquefasciatus compared with Ae. aegypti. Conclusion/significanceFludora Co-Max EW induced high mortality and knockdown effects against wild insecticide-resistant Ae. aegypti and Cx. quinquefasciatus Abidjan strains and performed better than K-Othrine EC. The presence of flupyradifurone and transfluthrin (with new and independent modes of action) and FFAST technology in the current Fludora Co-Max EW formulation appears to have broadened its killing capacity. Fludora Co-Max EW is thus an effective adulticide and may be a useful tool for Aedes and Culex mosquito and arbovirus control in endemic areas. Author SummarySpace spraying of insecticides is an important tool to control Aedes and Culex mosquitoes and prevent the viral diseases (i.e. dengue, yellow fever, etc.) that they transmit. We studied the efficacy of the product Fludora Co-Max EW (a new space spray insecticide) against adult wild insecticide-resistant populations of Aedes aegypti and Culex quinquefasciatus mosquitoes from Abidjan, Cote dIvoire. We compared Fludora Co-Max EW knockdown and mortality effects in these mosquitoes with the local insecticide K-Othrine EC using ultra-low volume (ULV) and thermal fogging (TF) spraying outdoors and indoors. The product Fludora Co-Max EW induced high rates of knockdown and mortality (i.e. 80-100%) in these wild insecticide-resistant mosquitoes and performed better than the product K-Othrine EC. Additionally, ULV sprays of Fludora Co-Max EW demonstrated higher knockdown and killing efficacy at larger distances (i.e. up to 100 m) compared with TF. The higher efficacy of Fludora Co-Max EW may be due to the interaction of two unrelated insecticides, flupyradifurone and transfluthrin, in combination with Film Forming Aqueous Spray Technology (FFAST). Fludora Co-Max EW therefore appears to be an effective and useful tool to control adult populations of wild insecticide-resistant Aedes and Culex mosquitoes and may be recommended for preventing related mosquito-transmitted viral diseases.

ecology↗