Visible-light-mediated deuteration of silanes with deuterium oxide.

Isotopically labeled compounds are highly desirable as they can serve as both mechanistic probes in chemistry and diagnostic tools in medicinal research. Herein, we report an unprecedented visible-light-mediated metal-free deuteration of silanes using D2O as an inexpensive, readily available, and easy to handle deuterium source. A broad range of aryl- and alkyl-substituted silanes were deuterated with high deuterium incorporations and yields. Furthermore, a 100 gram-scale synthesis was demonstrated using continuous-flow micro-tubing reactors, where enhanced reaction efficiency was obtained. The photoredox-catalyzed polarity matched hydrogen atom transfer (HAT) between silanes and the thiol HAT catalyst was responsible for the efficient deuteration.

Force of Infection and True Infection Rate of Dengue in Singapore: Implications for Dengue Control and Management.

National data on dengue notifications do not capture all dengue infections and do not reflect the true intensity of disease transmission. To assess the true dengue infection rate and disease control efforts in Singapore, we conducted age-stratified serosurveys among residents after a 2013 outbreak that was the largest dengue outbreak on record. The age-weighted prevalence of dengue immunoglobulin G among residents was 49.8% (95% confidence interval: 48.4, 51.1) in 2013 and 48.6% (95% confidence interval: 47.0, 50.0) in 2017; prevalence increased with age. Combining these data with those from previous serosurveys, the year-on-year estimates of the dengue force of infection from 1930 to 2017 revealed a significant decrease from the late 1960s to the mid-1990s, after which the force of infection remained stable at approximately 10 per 1,000 persons per year. The reproduction number (R0) had also declined since the 1960s. The reduction in dengue transmission may be attributed to the sustained national vector program and partly to a change in the age structure of the population. The improved estimated ratio of notified cases to true infections, from 1:14 in 2005-2009 to 1:6 in 2014-2017, signifies that the national notification system, which relies on diagnosed cases, has improved over time. The data also suggest that the magnitudes of dengue epidemics cannot be fairly compared across calendar years and that the current disease control program remains applicable.

Clinical outcome and genetic differences within a monophyletic Dengue virus type 2 population.

The exact mechanisms of interplay between host and viral factors leading to severe dengue are yet to be fully understood. Even though previous studies have implicated specific genetic differences of Dengue virus (DENV) in clinical severity and virus attenuation, similar studies with large-scale, whole genome screening of monophyletic virus populations are limited. Therefore, in the present study, we compared 89 whole genomes of DENV-2 cosmopolitan clade III isolates obtained from patients diagnosed with dengue fever (DF, n = 58), dengue hemorrhagic fever (DHF, n = 30) and dengue shock syndrome (DSS, n = 1) in Singapore between July 2010 and January 2013, in order to determine the correlation of observed viral genetic differences with clinical outcomes. Our findings showed no significant difference between the number of primary and secondary infections that progressed to DHF and DSS (p>0.05) in our study cohort. Despite being highly homogenous, study isolates possessed 39 amino acid substitutions of which 10 substitutions were fixed in three main groups of virus isolates. None of those substitutions were specifically associated with DHF and DSS. Notably, two evolutionarily unique virus groups possessing C-P43T+NS1-S103T+NS2A-V83I+NS3-R337K+ NS3-I600T+ NS5-P136S and NS2A-T119N mutations were exclusively found in patients with DF, the benign form of DENV infections. Those mutants were significantly associated with mild disease outcome. These observations indicated that disease progression into DHF and DSS within our patient population was more likely to be due to host than virus factors. We hypothesize that selection for potentially less virulent groups of DENV-2 in our study cohort may be an evolutionary adaptation of viral strains to extend their survival in the human-mosquito transmission cycle.

Diagnosing dengue at the point-of-care: utility of a rapid combined diagnostic kit in Singapore.

WHO recommendations for dengue diagnosis require laboratory facilities. Antibody-based rapid diagnostic tests (RDTs) have performed poorly, and clinical diagnosis remains the mainstay in dengue-endemic countries. We evaluated a combination antigen-antibody RDT for point-of-care testing in a high-prevalence setting. In this prospective cohort study, adults were enrolled from a tertiary infectious disease centre for evaluation of undifferentiated febrile illness from October 2011 to May 2012. SD Bioline Dengue Duo was evaluated at point-of-care against a WHO-based reference standard of viral isolation, RT-PCR, NS1-, IgM-, and IgG-ELISA. 246 adults were enrolled (median age 34 years, range 18-69), of which 197 could be confirmed definitively as either dengue or non-dengue. DENV-2 was the predominant serotype (79.5%) and the ratio of primary to secondary cases was 1∶1.1. There were no test failures and minimal interobserver variation with a Fleiss' kappa of 0.983 (95% CI 0.827-1.00). Overall sensitivity and specificity were 93.9% (95% CI 88.8-96.8%) and 92.0% (95% CI 81.2-96.9%) respectively. Using WHO clinical criteria alone for diagnosis had similar sensitivities (95.9%, 95% CI 91.4-98.1%) and lower specificities (20.0%, 95% CI 11.2-33.0%). No significant difference in performance was found when testing early versus late presenters, primary versus secondary cases, or DENV-1 versus DENV-2 infections. The use of a combination RDT fulfills WHO ASSURED criteria for point-of-care testing and can enhance dengue diagnosis in an endemic setting. This has the potential to markedly improve clinical management of dengue in the field.

Dengue virus surveillance in Singapore reveals high viral diversity through multiple introductions and in situ evolution.

Dengue fever, a vector-borne disease, has caused tremendous burden to countries in the tropics and sub tropics. Over the past 20 years, dengue epidemics have become more widespread, severe and frequent. This study aims to understand the dynamics of dengue viruses in cosmopolitan Singapore. Envelope protein gene sequences of all four dengue serotypes (DENV-1-DENV-4) obtained from human sera in Singapore (2008-2010) revealed that constant viral introductions and in situ evolution contribute to viral diversity in Singapore and play important roles in shaping the epidemiology of dengue in the island state. The diversity of dengue viruses reported here could be a reflection of the on-going dengue situation in the region given Singapore's location in a dengue hyperendemic region and its role as the regional hub for travels and trade. Though cosmopolitan genotype of DENV-2 has remained as the predominant strain circulating in Singapore, we uncovered evidence of in situ evolution which could possibly result in viruses with improved fitness. While we have previously shown that a switch in the predominant dengue serotype could serve as a warning for an impending outbreak, our current data shows that a replacement of a predominant viral clade, even in the absence of a switch in predominant serotype, could signal a possible increase in dengue transmission. The circulating dengue viruses in Singapore are highly diverse, a situation which could offer ample opportunities for selection of strains of higher fitness, thus increasing the risk of outbreaks despite a low Aedes population.