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A persistently replicating SARS-CoV-2 variant derived from an asymptomatic individual
Francesca Caccuri1, Alberto Zani1, Serena Messali1
1Department of Molecular and Translational Medicine, Section of Microbiology, University of Brescia, Brescia, Italy.
Journal of Translational Medicine
|September 24, 2020
Summary
A new SARS-CoV-2 strain (GZ69) identified in asymptomatic individuals shows increased replication in cell cultures. This variant differs genetically from earlier strains, highlighting the evolution of the virus and the need for continued surveillance.
Area of Science:
- Virology
- Genetics
- Epidemiology
Background:
- Clinical characteristics of Coronavirus Disease 2019 (COVID-19) have evolved since the initial SARS-CoV-2 outbreak.
- Emerging data suggest intra-host and inter-host viral evolution favoring milder SARS-CoV-2 strains.
- Understanding SARS-CoV-2 evolution and host adaptation requires investigating recent circulating strains.
Purpose of the Study:
- To investigate the genetic and phenotypic characteristics of recently circulating SARS-CoV-2 strains.
- To understand the evolution of SARS-CoV-2 pathogenicity and its adaptation to the human host.
Main Methods:
- Nasopharyngeal swabs were collected during early (March 2020) and late (May 2020) epidemic phases in Brescia, Italy.
- SARS-CoV-2 strains (AP66 and GZ69) were isolated from high viral load specimens and propagated in Vero E6 cells.
- Viral replication was quantified by qPCR, and genotypic characterization was performed using next-generation sequencing and in silico analysis.
Main Results:
- The SARS-CoV-2 GZ69 strain, isolated from an asymptomatic individual, demonstrated significant replication in Vero E6 cells without evident cytopathic effects.
- GZ69 infection sustained productive replication comparable to a cytopathic strain (AP66) through multiple cell culture passages.
- Whole genome sequencing revealed 9 nucleotide differences between GZ69 and AP66, resulting in 6 non-synonymous substitutions in ORF1ab, S, and N proteins.
Conclusions:
- The identification of the unique SARS-CoV-2 GZ69 strain underscores the importance of characterizing variants from asymptomatic or paucisymptomatic individuals.
- Further studies are needed to analyze the selection processes driving viral mutations within the human host.
- This research provides insights into the ongoing evolution of SARS-CoV-2.
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