RESUMO
The 2019 novel coronavirus disease (COVID-19) outbreaks that emerged in Wuhan city, Hubei province, have led to a formidable number of confirmed cases that resulted in >5,700 deaths globally, including 143 countries in all 6 continents. The World Health Organization declared a Public Health Emergency of International Concern with a very high level of global risk assessment. Severe acute respiratory syndrome (SARS)-coronavirus-2 (SARS-CoV-2), the agent of COVID-19, has >79% nucleotide sequence homology to SARS-CoV; therefore, both belong to the genus betacoronavirus and subgenus sarbecovirus. The S1 domains of the two appeared to share the cellular receptor ACE2, but revealed a much higher S1-ACE2 binding affinity. As seen in many other human coronaviruses, SARS-CoV-2 also shows respiratory infection, but the basic reproductive number (R₀) in transmission and the clinical latency are quite dissimilar from those of SARS- or MERS-CoVs. Many scientists infer that the time point of cross-barrier transfer from bats to mediate animals or to humans should be a rather recent event based on the full-length genome analyses obtained from the very first patients. Copy-choice polymerization, which often leads to a significant genome recombination rate in most coronaviruses, predicts the continued emergence of novel coronaviruses.