Origins and Evolution of Seasonal Human Coronaviruses

Four seasonal human coronaviruses (sHCoVs) are endemic globally (229E, NL63, OC43, and HKU1), accounting for 5-30% of human respiratory infections. However, the epidemiology and evolution of these CoVs remain understudied due to their association with mild symptomatology. Using a multigene and complete genomes analysis approach, we find the evolutionary histories of sHCoVs to be more complex than previously recognized, owing to frequent recombination of CoVs, including within and between sHCoVs. Within sHCoV recombination rate was highest for 229E and OC43, and within genus highest for betaCoVs, whereas substitutions per recombination event inversely highest in NL63 and HKU1, and the alphaCoVs. Depending on the gene studied, OC43 may have ungulate, canine, or rabbit CoV ancestors, while 229E may have origins in a bat, camel or an unsampled intermediate host. HKU1 had the earliest most recent common ancestor (MRCA: 1809-1899), comprised two genetically divergent genotypes (A and B) possibly representing two independent transmission events from murine CoVs, and genotype B was genetically more diverse than all the other sHCoVs. Finally, we found shared amino acid substitutions in multiple proteins along the non-human to sHCoV host-jump branches. The complex evolution of CoVs and their frequent host switches could benefit from continued surveillance of CoVs across non-human hosts.

Epidemiology and genetic diversity of SARS-CoV-2 lineages circulating in Africa

COVID-19 disease dynamics have been widely studied in different settings around the globe, but little is known about these patterns in the African continent. To investigate the epidemiology and genetic diversity of SARS-CoV-2 lineages circulating in Africa, more than 2400 complete genomes from 33 African countries were retrieved from the GISAID database and analyzed. We investigated their diversity using various clade and lineage nomenclature systems, reconstructed their evolutionary divergence and history using maximum likelihood inference methods, and studied the case and death trends in the continent. We also examined potential repeat patterns and motifs across the sequences. In this study, we show that after almost one year of the COVID-19 pandemic, only 143 out of the 782 Pango lineages found worldwide circulated in Africa, with five different lineages dominating in distinct periods of the pandemic. Analysis of the number of reported deaths in Africa also revealed large heterogeneity across the continent. Phylogenetic analysis revealed that African viruses cluster closely with those from all continents but more notably with viruses from Europe. However, the extent of viral diversity observed among African genomes is closest to that of the Oceania outbreak, most likely due to genomic under-surveillance in Africa. We also identified two motifs that could function as integrin-binding sites and N-glycosylation domains. These results shed light on the evolutionary dynamics of the circulating viral strains in Africa, elucidate the functions of protein motifs present in the genome sequences, and emphasize the need to expand genomic surveillance efforts in the continent to better understand the molecular, evolutionary, epidemiological, and spatiotemporal dynamics of the COVID-19 pandemic in Africa.