23 research outputs found
The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance.
Investment in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing in Africa over the past year has led to a major increase in the number of sequences that have been generated and used to track the pandemic on the continent, a number that now exceeds 100,000 genomes. Our results show an increase in the number of African countries that are able to sequence domestically and highlight that local sequencing enables faster turnaround times and more-regular routine surveillance. Despite limitations of low testing proportions, findings from this genomic surveillance study underscore the heterogeneous nature of the pandemic and illuminate the distinct dispersal dynamics of variants of concern-particularly Alpha, Beta, Delta, and Omicron-on the continent. Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve while the continent faces many emerging and reemerging infectious disease threats. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century
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
Measurements of Aqueous Droplet Evaporation Rate as a Function of Solute Species
The water content of atmospheric particles determines their size and solute concentration, and thus their phase, gas uptake, reactivity, optical properties, and cloud-forming properties. I have measured the evaporation rate of water from binary and ternary solution droplets using an ultrasonic levitator, and developed a simple model to predict the change in droplet size as a function of solute concentration. The simple model agrees well with experimental results for solutions of simple, non-ammonium salts, and may be used for organic acids with parameterized water activity data. For ammonium chloride and ammonium sulfate droplets, the experimental evaporation rate of subsaturated solutions exceeds the simple model's prediction. For ternary malonic acid/ammonium sulfate/water droplets, the effect of solutes on the evaporation rate of water from subsaturated solutions appears to be additive, and at higher concentrations a drastic reduction to evaporation rate is observed, suggesting that a highly viscous phase is formed.M.Sc
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Water Evaporation from Acoustically Levitated Aqueous Solution Droplets
We present a systematic
study of the effect of solutes on the evaporation
rate of acoustically levitated aqueous solution droplets by suspending
individual droplets in a zero-relative humidity environment and measuring
their size as a function of time. The ratios of the early time evaporation
rates of six simple salts (NaCl, NaBr, NaNO<sub>3</sub>, KCl, MgCl<sub>2</sub>, CaCl<sub>2</sub>) and malonic acid to that of water are
in excellent agreement with predictions made by modifying the Maxwell
equation to include the time-dependent water activity of the evaporating
aqueous salt solution droplets. However, the early time evaporation
rates of three ammonium salt solutions (NH<sub>4</sub>Cl, NH<sub>4</sub>NO<sub>3</sub>, (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>) are not
significantly different from the evaporation rate of pure water. This
finding is in accord with a previous report that ammonium sulfate
does not depress the evaporation rate of its solutions, despite reducing
its water vapor pressure, perhaps due to specific surface effects.
At longer evaporation times, as the droplets approach crystallization,
all but one (MgCl<sub>2</sub>) of the solution evaporation rates are
well described by the modified Maxwell equation
Interplay between Size, Composition, and Phase Transition of Nanocrystalline Cr<sup>3+</sup>-Doped BaTiO<sub>3</sub> as a Path to Multiferroism in Perovskite-Type Oxides
Multiferroics, materials that exhibit coupling between
spontaneous
magnetic and electric dipole ordering, have significant potential
for high-density memory storage and the design of complex multistate
memory elements. In this work, we have demonstrated the solvent-controlled
synthesis of Cr<sup>3+</sup>-doped BaTiO<sub>3</sub> nanocrystals
and investigated the effects of size and doping concentration on their
structure and phase transformation using X-ray diffraction and Raman
spectroscopy. The magnetic properties of these nanocrystals were studied
by magnetic susceptibility, magnetic circular dichroism (MCD), and
X-ray magnetic circular dichroism (XMCD) measurements. We observed
that a decrease in nanocrystal size and an increase in doping concentration
favor the stabilization of the paraelectric cubic phase, although
the ferroelectric tetragonal phase is partly retained even in ca.
7 nm nanocrystals having the doping concentration of ca. 5%. The chromiumÂ(III)
doping was determined to be a dominant factor for destabilization
of the tetragonal phase. A combination of magnetic and magneto-optical
measurements revealed that nanocrystalline films prepared from as-synthesized
paramagnetic Cr<sup>3+</sup>-doped BaTiO<sub>3</sub> nanocrystals
exhibit robust ferromagnetic ordering (up to ca. 2 ÎĽ<sub>B</sub>/Cr<sup>3+</sup>), similarly to magnetically doped transparent conducting
oxides. The observed ferromagnetism increases with decreasing constituent
nanocrystal size because of an enhancement in the interfacial defect
concentration with increasing surface-to-volume ratio. Element-specific
XMCD spectra measured by scanning transmission X-ray microscopy (STXM)
confirmed with high spatial resolution that magnetic ordering arises
from Cr<sup>3+</sup> dopant exchange interactions. The results of
this work suggest an approach to the design and preparation of multiferroic
perovskite materials that retain the ferroelectric phase and exhibit
long-range magnetic ordering by using doped colloidal nanocrystals
with optimized composition and size as functional building blocks