In January 2020, a novel virus later named severe acute respiratory syndrome coronavirus (SARS-CoV-2) was isolated from the broncho-alveolar fluid of a patient in Wuhan, People’s Republic of China, suffering from what became known as coronavirus disease 2019 (COVID-19). SARS-CoV-2 is highly transmissible and pathogenic. Until present (October 2020), it has infected tens of millions of individuals, causing more than a million deaths and debilitating the economy.
Coronaviruses (CoV) are large, spherical, enveloped RNA viruses with distinct protruding spike glycoproteins visible on the viral surface. The name is derived from the Latin “corona”, which means crown or halo, referencing the characteristic morphology when viewed under an electron microscope (Zuckerman 2009, Perlman 2020). Structural proteins include envelope (E), matrix (M), and nucleocapsid (N).CoV contain a single strand of positive-sense RNA. Their genome size ranges from c. 26 to 32 kilobases, placing them among the known RNA viruses with the largest genomes.
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The family Coronaviridae belongs to the order Nidovirales, suborder Cornidovirineae. Subfamily Orthocoronavirinae includes four genera: alpha-, beta-, delta- and gammacoronavirus. Genera alpha- and betacoronavirus contain several human-pathogenic subgenera and species. SARS-CoV-2 is a previously unknown betacoronavirus in subgenus Sarbecovirus, like its close relative, severe acute respiratory syndrome-related coronavirus (SARS-CoV). Other notable beta-CoV are Middle East respiratory syndrome-related CoV (MERS-CoV) in subgenus Merbecovirus as well as human CoV HKU1 and human CoV OC43, species Betacoronavirus 1, both in subgenus Embecovirus.
Species in of the family Coronaviridae infect various species of animals – humans, other mammals, and birds – causing a broad spectrum of different diseases. Human CoV are primarily respiratory pathogens but may cause enteric disease. Respiratory illness caused by human CoV HCoV-OC43, HCoV-HKU1, HCoV-229E, and HCoV-NL63 is usually mild and “common cold”-like and thus not of major public health concern (Korsman 2012). The highly pathogenic CoV affecting humans cause severe acute respiratory infections often resulting in serious disease and death is was caused by the novel SARS-CoV and MERS-CoV. There is strong evidence that these viruses emerged recently from animal reservoirs, originating in bats and transmitted to man via intermediate host species. Intra- and inter-species transmission of CoVs, and genetic recombination events contribute to the emergence of new CoV strains.
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The following sections will review coronaviruses in general with a more detailed appraisal of the origin, evolution, virological structure and pathogenesis of SARS-CoV-2 to expand knowledge pertaining to COVID-19 and prospective anti-viral and vaccine therapies.
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