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Origin and evolution of (A) SARS-CoV, (B) MERS-CoV and (C) SARS-CoV-2 in the various hosts. Initially all viruses existed in diverse bat species as CoV-related viruses (SARSr-CoV, MERSr-CoV and SARSr-CoV-2); sequential mutations and recombinations allow them to adapt to intermediate hosts and finally humans [15].
