The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Endothelin-1 as a mediator of endothelial cell-pericyte interactions in bovine brain capillaries

International audienceEndothelial cells and pericytes are closely associated in brain capillaries. Together with astrocytic foot processes, they form the blood-brain barrier. Capillaries were isolated from bovine brain cortex. Pure populations of endothelial cells and pericytes were isolated and cultured in vitro. Polarized monolayers of endothelial cells preferentially secreted immunoreactive endothelin-1 (Et-1) at their abluminal (brain-facing) membrane. They did not express receptors for Et-1. Pericytes expressed BQ-123-sensitive ETA receptors for endothelins as evidenced by 125I-Et-1 binding experiments. These receptors were coupled to phospholipase C as demonstrated by intracellular calcium measurements using indo-1-loaded cells. Addition of Et-1 to pericytes induced marked changes in the cell morphology that were associated with a reorganization of F-actin and intermediate filaments. It is concluded that Et-1 is a paracrine mediator at the bovine blood-brain barrier and that capillary pericytes are target cells for endothelium-derived Et-1

Charge transport through one-dimensional Moiré crystals

Moiré superlattices were generated in two-dimensional (2D) van der Waals heterostructures and have revealed intriguing electronic structures. The appearance of mini-Dirac cones within the conduction and valence bands of graphene is one of the most striking among the new quantum features. A Moiré superstructure emerges when at least two periodic sub-structures superimpose. 2D Moiré patterns have been particularly investigated in stacked hexagonal 2D atomic lattices like twisted graphene layers and graphene deposited on hexagonal boron-nitride. In this letter, we report both experimentally and theoretically evidence of superlattices physics in transport properties of one-dimensional (1D) Moiré crystals. Rolling-up few layers of graphene to form a multiwall carbon nanotube adds boundaries conditions that can be translated into interference fringes-like Moiré patterns along the circumference of the cylinder. Such a 1D Moiré crystal exhibits a complex 1D multiple bands structure with clear and robust interband quantum transitions due to the presence of mini-Dirac points and pseudo-gaps. Our devices consist in a very large diameter (>80nm) multiwall carbon nanotubes of high quality, electrically connected by metallic electrodes acting as charge reservoirs. Conductance measurements reveal the presence of van Hove singularities assigned to 1D Moiré superlattice effect and illustrated by electronic structure calculations

Hunting, Sale, and Consumption of Bushmeat Killed by Lead-Based Ammunition in Benin

Human consumption of animal meat killed by lead ammunition has been reported as a risk factor for elevated blood lead levels. However, little is known about how meat killed by lead ammunition is hunted, prepared, sold, and consumed. We explored the process from hunting to consumption within communities in Benin from the perspective of preventive measures. We conducted 38 semi-structured interviews with hunters (n = 9) and sellers (n = 8) of bushmeat and families (n = 21) as consumers of bushmeat killed by lead ammunition. Data were transcribed, translated, and coded for analysis. We conducted content analysis to identify and describe key themes and processes from hunting to consumption. Many hunters (n = 7/9) used lead-based ammunition. After the meat is hunted, market sellers often buy it directly from the hunters. Amongst the hunters and sellers, few (n = 4/17) acknowledged removing the meat impacted by lead shot prior to sale. Many families (n = 15/21) mentioned consumption of the hunted bushmeat. The meat is cooked before sharing with children. Many families (n = 19/21) mentioned they look for the remains of the lead shot or remove the meat impacted by the shot. The finding suggests that hunting, sale, and consumption of bushmeat killed by lead ammunition are well-known practices in Allada, Benin. The bushmeat often hunted illegally with lead shot is sold in the markets and eventually consumed by families who attempt to clean the meat impacted by the lead shot before cooking it

Selection of a Relevant In Vitro Blood-Brain Barrier Model to Investigate Pro-Metastatic Features of Human Breast Cancer Cell Lines.

International audienceAround 7-17% of metastatic breast cancer patients will develop brain metastases, associated with a poor prognosis. To reach the brain parenchyma, cancer cells need to cross the highly restrictive endothelium of the Blood-Brain Barrier (BBB). As treatments for brain metastases are mostly inefficient, preventing cancer cells to reach the brain could provide a relevant and important strategy. For that purpose an in vitro approach is required to identify cellular and molecular interaction mechanisms between breast cancer cells and BBB endothelium, notably at the early steps of the interaction. However, while numerous studies are performed with in vitro models, the heterogeneity and the quality of BBB models used is a limitation to the extrapolation of the obtained results to in vivo context, showing that the choice of a model that fulfills the biological BBB characteristics is essential. Therefore, we compared pre-established and currently used in vitro models from different origins (bovine, mice, human) in order to define the most appropriate tool to study interactions between breast cancer cells and the BBB. On each model, the BBB properties and the adhesion capacities of breast cancer cell lines were evaluated. As endothelial cells represent the physical restriction site of the BBB, all the models consisted of endothelial cells from animal or human origins. Among these models, only the in vitro BBB model derived from human stem cells both displayed BBB properties and allowed measurement of meaningful different interaction capacities of the cancer cell lines. Importantly, the measured adhesion and transmigration were found to be in accordance with the cancer cell lines molecular subtypes. In addition, at a molecular level, the inhibition of ganglioside biosynthesis highlights the potential role of glycosylation in breast cancer cells adhesion capacities

Giant spin signals in chemically functionalized multiwall carbon nanotubes

Transporting quantum information such as the spin information over micrometric or even millimetric distances is a strong requirement for the next-generation electronic circuits such as low-voltage spin-logic devices. This crucial step of transportation remains delicate in nontopologically protected systems because of the volatile nature of spin states. Here, a beneficial combination of different phenomena is used to approach this sought-after milestone for the beyond–Complementary Metal Oxide Semiconductor (CMOS) technology roadmap. First, a strongly spin-polarized charge current is injected using highly spin-polarized hybridized states emerging at the complex ferromagnetic metal/molecule interfaces. Second, the spin information is brought toward the conducting inner shells of a multiwall carbon nanotube used as a confined nanoguide benefiting from both weak spin-orbit and hyperfine interactions. The spin information is finally electrically converted because of a strong magnetoresistive effect. The experimental results are also supported by calculations qualitatively revealing exceptional spin transport properties of this system

Charge injection and transport properties of large area organic junctions based on aryl thin films covalently attached to a multilayer graphene electrode

International audienceThe quantum interaction between molecules and electrode's material at molecules/electrode interfaces is a major ingredient in the electronic transport properties of organic junctions. Driven by the coupling strength between the two materials, it results mainly in a broadening and an energy shift of the interacting molecular orbitals. Using new electrodes materials, such as the recent semi-conducting two-dimensional nanomaterials, has become a recent challenge in the field of molecular/organic electronics that opens new possibilities for controlling the interfacial electronic properties and thus the charge injection properties. In this article, we report the use of atomically thin two-dimensional multilayer graphene films as base electrode in organic junctions with a vertical architecture. The interfacial electronic structure dominated by the covalent bonding between bis-thienyl benzene diazonium-based molecules and the multilayer graphene electrode has been probed by ultraviolet photoelectron spectroscopy and the results compared with those obtained on junctions with standard Au electrodes. Room temperature injection properties of such interfaces have been also explored by electronic transport measurements. We find that, despite strong variations of the density of states, the Fermi energy and the injection barriers, both organic junctions with Au base electrodes and multilayer graphene base electrodes show similar electronic responses. We explain this observation by the strong orbital coupling occurring at the bottom electrode/ bis-thienyl benzene molecules interface and by the pinning of the hybridized molecular orbitals

Réussite scolaire, réussite professionnelle, l'apport des données longitudinales. XXIes journées d'étude sur les données longitudinales dans l'analyse du marché du travail, Dijon, 19-20 juin 2014

International audienceDans un contexte où s'accumulent les difficultés scolaires au sein du système éducatif, puis les difficultés professionnelles sur un marché du travail de plus en plus sélectif, la question de la réussite se pose souvent en creux dans les interrogations de nombreux chercheurs. Elle constitue le thème central de ces XXIes journées du longitudinal

Lead Exposure in Infancy and Subsequent Growth in Beninese Children

International audienceStudies suggest that elevated postnatal blood lead levels (BLLs) are negatively associated with child growth. This study aimed to investigate the associations of childhood BLLs at age one year and growth outcomes at age six years (n = 661) in a cohort of children in Allada, Benin. The growth outcomes studied are weight-for-age Z-score (WAZ), height-for-age Z-score (HAZ), BMI-for-age Z-score (BMIZ), weight-for-height Z-score (WHZ), head circumference (HC), growth velocities, underweight, stunting, and wasting. Multivariable regression models examined the associations between BLLs and growth outcomes, with adjustment for potential confounders. The geometric mean BLLs was 59.3 μg/L and 82% of children had BLLs >35 μg/L at the age of 12.8 months. After adjusting for confounding factors, no overall association was found between BLL quartiles and HAZ, WAZ, BMIZ, WHZ, growth velocities, wasting, and underweight. However, boys in the highest quartile had a 1.02 cm lower HC (95% CI: [−1.81, −0.24]) as compared to the lowest quartile. Furthermore, an increased odds of being stunted was observed in children in the highest quartile of exposure compared to the first (OR: 2.43; 95% CI: [1.11–5.33]) which remained statistically significant only among girls in sex-specific strata. Blood lead was found to be associated with an increased risk of childhood stunting and a lower head circumference in a resource-limited setting