Reinfection with SARS-CoV-2: discrete SIR (Susceptible, Infected, Recovered) modeling using empirical infection data
JMIR Public Health and Surveillance JMIR Publications 6:4 (2020) e21168
Abstract:
BACKGROUND:The novel coronavirus SARS-CoV-2, which causes the COVID-19 disease, has resulted in a global pandemic. Since its emergence in December 2019, the virus has infected millions of people, caused the deaths of hundreds of thousands, and resulted in incalculable social and economic damage. Understanding the infectivity and transmission dynamics of the virus is essential to determine how best to reduce mortality while ensuring minimal social restrictions on the lives of the general population. Anecdotal evidence is available, but detailed studies have not yet revealed whether infection with the virus results in immunity.
OBJECTIVE:
The objective of this study was to use mathematical modeling to investigate the reinfection frequency of COVID-19.
METHODS:
We have used the SIR (Susceptible, Infected, Recovered) framework and random processing based on empirical SARS-CoV-2 infection and fatality data from different regions to calculate the number of reinfections that would be expected to occur if no immunity to the disease occurred.
RESULTS:
Our model predicts that cases of reinfection should have been observed by now if primary SARS-CoV-2 infection did not protect individuals from subsequent exposure in the short term; however, no such cases have been documented.
CONCLUSIONS:
This work concludes that infection with SARS-CoV-2 provides short-term immunity to reinfection and therefore offers useful insight for serological testing strategies, lockdown easing, and vaccine development.
High-throughput nitrogen-vacancy center imaging for nanodiamond photophysical characterization and pH nanosensing
Nanoscale Royal Society of Chemistry 12:42 (2020) 21821-21831
Abstract:
The fluorescent nitrogen-vacancy (NV) defect in diamond has remarkable photophysical properties, including high photostability which allows stable fluorescence emission for hours; as a result, there has been much interest in using nanodiamonds (NDs) for applications in quantum optics and biological imaging. Such applications have been limited by the heterogeneity of NDs and our limited understanding of NV photophysics in NDs, which is partially due to the lack of sensitive and high-throughput methods for photophysical analysis of NDs. Here, we report a systematic analysis of NDs using two-color wide-field epifluorescence imaging coupled to high-throughput single-particle detection of single NVs in NDs with sizes down to 5-10 nm. By using fluorescence intensity ratios, we observe directly the charge conversion of single NV center (NV- or NV0) and measure the lifetimes of different NV charge states in NDs. We also show that we can use changes in pH to control the main NV charge states in a direct and reversible fashion, a discovery that paves the way for performing pH nanosensing with a non-photobleachable probe.Transcription reinitiation by recycling RNA polymerase that diffuses on DNA after releasing terminated RNA
Nature Communications Springer Nature 11 (2020) 450
Abstract:
Despite extensive studies on transcription mechanisms, it is unknown how termination complexes are disassembled, especially in what order the essential components dissociate. Our single-molecule fluorescence study unveils that RNA transcript release precedes RNA polymerase (RNAP) dissociation from the DNA template much more often than their concurrent dissociations in intrinsic termination of bacterial transcription. As termination is defined by the release of product RNA from the transcription complex, the subsequent retention of RNAP on DNA constitutes a previously unidentified stage, termed here as recycling. During the recycling stage, post-terminational RNAPs one-dimensionally diffuse on DNA in downward and upward directions, and can initiate transcription again at the original and nearby promoters in the case of retaining a sigma factor. The efficiency of this event, termed here as reinitiation, increases with supplement of a sigma factor. In summary, after releasing RNA product at intrinsic termination, recycling RNAP diffuses on the DNA template for reinitiation most of the time.Single-Molecule FRET Assay for Studying Cotranscriptional RNA Folding.
Methods in molecular biology (Clifton, N.J.) 2106 (2020) 271-282
Abstract:
Cotranscriptional RNA folding plays important roles in gene regulation steps such as splicing, transcription termination, and translation initiation. Progression of our understanding of cotranscriptional RNA folding mechanisms is still retarded by the lacking of experimental tools to study the kinetics of cotranscriptional RNA folding properly. In this chapter, we describe fluorescence resonance energy transfer (FRET) assay that enables the study of RNA cotranscriptional folding at the single-molecule level.Transient non-specific DNA binding dominates the target search of bacterial DNA-binding proteins
(2020)