ABSTRACT
The SARS-CoV-2 Delta variant has spread rapidly worldwide. To provide data on its virological profile, we here report the first local transmission of Delta in mainland China. All 167 infections could be traced back to the first index case. Daily sequential PCR testing of quarantined individuals indicated that the viral loads of Delta infections, when they first become PCR-positive, were on average ~1000 times greater compared to lineage A/B infections during the first epidemic wave in China in early 2020, suggesting potentially faster viral replication and greater infectiousness of Delta during early infection. The estimated transmission bottleneck size of the Delta variant was generally narrow, with 1-3 virions in 29 donor-recipient transmission pairs. However, the transmission of minor iSNVs resulted in at least 3 of the 34 substitutions that were identified in the outbreak, highlighting the contribution of intra-host variants to population-level viral diversity during rapid spread.
Subject(s)
COVID-19/transmission , Contact Tracing/methods , Disease Outbreaks/prevention & control , SARS-CoV-2/isolation & purification , Animals , COVID-19/epidemiology , COVID-19/virology , Chlorocebus aethiops , Humans , RNA-Seq/methods , Reverse Transcriptase Polymerase Chain Reaction , SARS-CoV-2/genetics , SARS-CoV-2/physiology , Time Factors , Vero Cells , Viral Load/genetics , Viral Load/physiology , Virus Replication/genetics , Virus Replication/physiology , Virus Shedding/genetics , Virus Shedding/physiologyABSTRACT
Severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) with unknown origin spread rapidly to 222 countries, areas or territories. To investigate the genomic evolution and variation in the early phase of COVID-19 pandemic in Guangdong, 60 specimens of SARS-CoV-2 were used to perform whole genome sequencing, and genomics, amino acid variation and Spike protein structure modeling analyses. Phylogenetic analysis suggested that the early variation in the SARS-CoV-2 genome was still intra-species, with no evolution to other coronaviruses. There were one to seven nucleotide variations (SNVs) in each genome and all SNVs were distributed in various fragments of the genome. The Spike protein bound with human receptor, an amino acid salt bridge and a potential furin cleavage site were found in the SARS-CoV-2 using molecular modeling. Our study clarified the characteristics of SARS-CoV-2 genomic evolution, variation and Spike protein structure in the early phase of local cases in Guangdong, which provided reference for generating prevention and control strategies and tracing the source of new outbreaks.