Biology subjects

Becker, S. C.

Publications and source records attributed to Becker, S. C..

4 recordsLinked to original sources

bioRxiv2026

Field-isolate recombinant tick-borne encephalitis viruses define reporter-stability guidelines for antiviral screening in flaviviruses

As arthropod-borne viruses continue to threaten populations globally, there is a pressing need for experimental systems that enable rapid antiviral discovery. Reverse-genetics platforms producing recombinant reporter orthoflaviviruses have been developed to address this gap. Here, we present two new recombinant tick-borne encephalitis viruses (TBEVrec) generated on a European-subtype Haselmuehl Tiho1 isolate backbone. A reporter gene, either eGFP or Nluc, was inserted in the capsid-coding region of the genome downstream of the capsid RNA regulatory signal and separated from the complete viral polyprotein by a 2A self-cleaving peptide. TBEVrec was better rescued using the circular polymerase extension reaction (CPER) than with the infectious subgenomic amplicon (ISA) method. TBEVrec replicated efficiently in relevant human cell lines, with comparable replication to wild-type TBEV in a neuronal cell line and moderately reduced titers and RNA levels in immune-derived cell lines. Using either eGFP or Nluc, we illustrate how TBEVrec enabled high-content RNAi screening, highlighting Nucleolin and PRKD1 as potential TBEV host factors, and drug testing on a benchtop plate reader. Nanopore sequencing of the eGFP insert revealed that the reporter is excised without affecting flanking regions. Comparative analysis of eGFP and Nluc further shows that this instability is time- and cell type-dependent, and that Nluc is comparatively more stable. From these observations, we outline safeguards and design principles that are broadly applicable both to the rescue of existing constructs and to the design of future recombinant reporter virus platforms.

microbiology↗

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↗

bioRxiv2020

A developmental analysis of juxtavascular microglia dynamics and interactions with the vasculature

Microglia, the resident macrophages of the central nervous system (CNS), are dynamic cells, constantly extending and retracting their processes as they contact and functionally regulate neurons and other glial cells. There is far less known about microglia-vascular interactions, particularly under healthy steady-state conditions. Here, we use the male and female mouse cerebral cortex to show that a higher percentage of microglia associate with the vasculature during the first week of postnatal development compared to older ages and the timing of these associations are dependent on the fractalkine receptor (CX3CR1). Similar developmental microglia-vascular associations were detected in the prenatal human brain. Using live imaging in mice, we found that juxtavascular microglia migrated when microglia are actively colonizing the cortex and became stationary by adulthood to occupy the same vascular space for nearly 2 months. Further, juxtavascular microglia at all ages contact vascular areas void of astrocyte endfeet and the developmental shift in microglial migratory behavior along vessels corresponded to when astrocyte endfeet more fully ensheath vessels. Together, our data provide a comprehensive assessment of microglia-vascular interactions. They support a mechanism by which microglia use the vasculature to migrate within the developing brain parenchyma. This migration becomes restricted upon the arrival of astrocyte endfeet when juxtavascular microglia then establish a long-term, stable contact with the vasculature. SIGNIFICANCE STATEMENTWe report the first extensive analysis of juxtavascular microglia in the healthy, developing and adult brain. Live imaging revealed that juxtavascular microglia within the cortex are highly motile and migrate along vessels as they are colonizing cortical regions. Using confocal, expansion, super-resolution, and electron microscopy, we determined that microglia associate with the vasculature at all ages in areas lacking full coverage astrocyte endfoot coverage and motility of juxtavascular microglia ceases as astrocyte endfeet more fully ensheath the vasculature. Our data lay the fundamental groundwork to investigate microglia-astrocyte crosstalk and juxtavascular microglial function in the healthy and diseased brain. They further provide a potential vascular-dependent mechanism by which microglia colonize the brain to later regulate neural circuit development.

neuroscience↗