Unraveling varying spatiotemporal patterns of dengue and associated exposure-response relationships with environmental variables in Southeast Asian countries before and during COVID-19 (preprint)

The enforcement of COVID-19 interventions by diverse governmental bodies, coupled with the indirect impact of COVID-19 on short-term environmental changes (e.g. plant shutdowns lead to lower greenhouse gas emissions), influences the dengue vector. This provides a unique opportunity to investigate the impact of COVID-19 on dengue transmission and generate insights to guide more targeted prevention measures. We aim to compare dengue transmission patterns and the exposure-response relationship of environmental variables and dengue incidence in the pre- and during-COVID-19 to identify variations and assess the impact of COVID-19 on dengue transmission. We initially visualized the overall trend of dengue transmission from 2012-2022, then conducted two quantitative analyses to compare dengue transmission pre-COVID-19 (2017-2019) and during-COVID-19 (2020-2022). These analyses included time series analysis to assess dengue seasonality, and a Distributed Lag Non-linear Model (DLNM) to quantify the exposure-response relationship between environmental variables and dengue incidence. We observed that all subregions in Thailand exhibited remarkable synchrony with a similar annual trend except 2021. Cyclic and seasonal patterns of dengue remained consistent pre- and during-COVID-19. Monthly dengue incidence in three countries varied significantly. Singapore witnessed a notable surge during-COVID-19, particularly from May to August, with cases multiplying several times compared to pre-COVID-19, while seasonality of Malaysia weakened. Exposure-response relationships of dengue and environmental variables show varying degrees of change, notably in Northern Thailand, where the peak relative risk for the maximum temperature-dengue relationship rose from about 3 to 17, and the max RR of overall cumulative association 0-3 months of relative humidity increased from around 5 to 55. Our study is the first to compare dengue transmission patterns and their relationship with environmental variables before and during COVID-19, showing that COVID-19 has affected dengue transmission at both the national and regional level, and has altered the exposure-response relationship between dengue and the environment.

Phytochemicals Characterization of Lianqiao (Forsythia suspensa) extract and evaluation of its antivirus and antioxidant activities (preprint)

Forsythia suspensa (Lianqiao) has long been touted for its anti-viral effects in folklore. Although promising, limited research were conducted to evaluate its potential in defending the severe acute respiratory syndrome coronavirus (SARS-CoV-2). This study evaluated the fruits of Forsythia suspensa (Lianqiao), an important economic crop, for the chemical components of its water and ethanol extracts, along with their inhibitory effects on SARS-CoV-2 spike protein binding to angiotensin-converting enzyme 2 (ACE2), inhibitions of ACE2 activity, and capacities to scavenge the selected free radicals. A total of 42 compounds were tentatively identified in the extracts by HPLC-MS/MS analysis. Both water and ethanol extracts of Lianqiao showed great inhibition of ACE2 activity and the binding affinity between SARS CoV-2 spike protein and ACE2. Furthermore, the water extract had greater scavenging capacities against HO●, DPPH● and ABTS●+ than the ethanol extract. Findings of this research contribute to the knowledge of different extraction solvent systems and support the potential of Lianqiao in reducing the risk of coronavirus infection and alleviating the symptoms after infection.