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Coronaviruses (CoVs) are a large group of enveloped viruses with a positive-sense RNA that have characteristic spikes projecting from their surface. CoVs are well known for their large RNA genome (26-32 kb). They primarily affect mammals and birds, causing infections of the respiratory and gastrointestinal tracts. The emergence of human CoVs (HCoVs) has been reported once every ten years for the last three decades. The most recent emergence occurred in December 2019, when a new strain of CoVs named SARS-CoV-2 caused the coronavirus disease 2019 (COVID-19) pandemic, leaving a devastating impact on the global healthcare. The early cases were associated with the Huanan seafood market in Wuhan, although the exact origin of the virus is still being debated. Phylogenetic analysis reveals bats to be the reservoir hosts, but the intermediate host responsible for spill-over into the human population remains debatable. Accumulating evidence cites pangolins based on the similarity of receptor binding domain in spike protein; however, the search for a conclusive intermediate host that aided in the inter-species crossover is still underway. Advances have been made in our understanding of the functions of each structural protein, but certain non-structural proteins and accessory proteins are yet to be characterised. Owing to the large genetic diversity of CoVs that arise through recombination, genetic variation, or gene gains/losses, future re-emergence of CoVs are most likely. In this review, we provide an introduction to CoVs and discuss the origin, virology, genetics, phylogeny, and pathogenesis of SARS-CoV-2 based on relevant literature.
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