The African Centre of Excellence for the Genomics of Infectious Diseases [ACEGID], Redeemer’s University, Ede, Nigeria [RUN], and the Nigeria Centre for Disease Control [NCDC] report twenty-four [24] additional genome sequences of SARS-CoV-2 from Nigeria.
As a member of the Molecular Laboratory Network of the Nigeria Centre for Disease Control [NCDC], clinical specimens [specifically saliva, nasopharyngeal and nasal swabs] from suspected COVID-19 cases were sent to ACEGID, Redeemer’s University, for confirmatory testing, sequencing and molecular characterization.
Viral RNA was extracted using the QiAmp viral RNA mini kit [Qiagen]. RT-qPCR was carried out using the DAAN RT-qPCR assay which confirmed the presence of SARS-CoV-2 viral RNA. Metagenomic sequencing libraries were prepared from total RNA as we previously described [Matranga et al ., 2016], and sequenced using the two Illumina MiSeqs in the sequencing platform of ACEGID.
Genome Assembly and Quality control
We carried out genome assembly using our publicly available software [viral-ngs v2.0] implemented on the DNA nexus cloud-based platform. We assembled 24 genomes [18 full and 6 partials]. We carried out quality control using fastqc
Phylogenetics and Lineage Delineation
Representative HCoV whole genome sequences of each of the seven lineages circulating in Nigeria were obtained from GISAID and aligned with all full genomes from Nigeria so far. The sequences were aligned using MAFFT v7.310 [Katoh et al., 2009] and tree reconstruction using FastTree v2.1.11 [Price et al., 2009].
Four of our new sequences clustered closely together and formed a separate clade which strongly suggests local community transmission. Epidemiological data confirmed that all four sequences are from patients in a community in Ekiti State, Nigeria with three of these four patients being members of the same family.
We also observed a couple other new sequences clustering closely together, further investigation however revealed these sequences are from follow-up samples obtained from the same patients.
Using Pangolin software [Rambaut et al ., 2020], we assigned the sequences to global SARS-CoV-2 lineages, and this revealed four additional lineages [B.1.1, B.1.36, B.1.22, B.1.1.10] of the virus circulating in Nigeria.
Addition of these new lineages brings the total number of lineages circulating in Nigeria to seven (7). Sequences from these lineages from Nigeria are clustering with sequences from Asia, Europe, USA, Middle-East, Australia, and other African countries [Figure 1], indicating multiple introduction of multiple lineages [Figures 1&2] of the virus into the country.
Lineages are grouped according to named global outbreaks of the current pandemic** (Lineage A: China, South Korea, USA; Lineage B.1: UK, USA, Australia; Lineage B.1.1: UK, Australia, USA; Lineage B.1.1.10: UK, Iceland, Australia; Lineage B.1.22: Netherlands, Australia, Austria; Lineage B.1.36: Saudi Arabia, UK, Turkey; Lineage B.2.1: UK, Australia, USA).
Genome Annotation and Mutation Analysis
We performed genome annotation on all 42 genomes from Nigeria so far using Prokka version 1.14.6 with the SARS-CoV-2 reference genome [NCBI accession number – NC_045512.2] as guide.
A custom Bash script was used to extract the spike protein from each annotated output and generate a multi FASTA file containing all spike proteins. Quality control was done to exclude protein files that had missing information of up to 50 % from the analysis, yielding 26 genomes.
Multiple sequence alignment using MAFFT version 7.450 shows that 19 of the 26 genomes (73.1 %) have the Glycine (G) mutation in position 614, whilst 7 genomes (26.9 %) retain the wild type Aspartic acid (D) in that position.
This mutation has been recently been confirmed to be associated with higher transmission of SARS-CoV 2, hence dominating globally than the wild type [Korber et al. (2020)].
Temporal Analysis of SARS-CoV-2 Spike Protein Mutation
A temporal analysis of the D614G mutation shows that G614 mutation in the spike gene has increased over time compared to D614 wild-type in Nigeria, suggesting a higher rate of transmission of mutant viruses.
Source: virological.org
