AsianScientist (May 25, 2020) – A Shanghai study has identified two lineages of SARS-CoV-2 originating from one common ancestor in Wuhan city, both exhibiting similar virulence and clinical outcomes.
The study, which was published as an ‘accelerated article preview’ in Nature, also found that disease severity is determined by host factors, such as age, as opposed to virus factors, such as genomic variation.
In December 2019, a novel coronavirus SARS-CoV-2 emerged in the city of Wuhan in China’s Hubei province. Although the Huanan Seafood Wet Market is widely thought to be the original outbreak site of SARS-CoV-2, a significant number of the initial cases did not have contact with this market. This cast doubt on the singular event of zoonotic spillover to humans in the initial outbreak.
To understand the epidemiology and pathogenesis of COVID-19, a team led by Wang Shengyue, Chen Saijuan and Lu Hongzhou analyzed the clinical data from 326 confirmed cases of COVID-19 who were admitted into the Shanghai Public Health Clinical Center at Fudan University from January 20 to February 25.
The researchers then assembled genomic sequences from 112 sequencing samples and compared them against sequences in the Global Initiative on Sharing All Influenza Data (GISAID) dataset. First, the genomic sequences provided evidence that the viral genome is largely stable. Second, small sequence variations suggested two major lineages: one with contact history to the wet market, and the other with no exposure to the wet market. Time-resolved phylogeny analysis suggested that the earliest zoonotic spillover event might have occurred in late November 2019, which is in agreement with a report by Andersen et al. in Nature Medicine.
It was also important to investigate whether SARS-CoV-2 virulence has altered due to genomic sequence evolution during the spread of the disease. The study showed that infections from both viral lineages exhibited similar virulence and clinical outcomes, and that clinical outcomes were linked to host factors such as age, decreased lymphocyte count (especially reduced CD4+ and CD8+ T cell counts upon admission) and a cytokine storm (high levels of IL-6 and IL-8 during treatment).
“Two major lineages of the virus derived from one common ancestor may have originated independently from Wuhan in Dec 2019 and contributed to the current pandemic, although no major difference in clinical manifestation or transmissibility was found between them,” the authors wrote.
“The determinants of disease severity seemed to stem mostly from host factors such as age, lymphocytopenia and its associated cytokine storm, whereas viral genetic variation did not significantly affect the outcomes.”
The article can be found at: Zhang et al. (2020) Viral and Host Factors Related to the Clinical Outcome of COVID-19.
Source: Nature; Photo: Shutterstock.
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