At the end of 2019, a number of patients presented with viral pneumonias of unknown origin in Wuhan, China. A novel coronavirus was identified as the causative agent, provisionally named 2019 novel coronavirus (2019-nCoV). By the time of publication, more than 2000 cases of 2019-nCoV infection have been confirmed, mostly in people living in or visiting Wuhan. The authors sequenced samples from bronchoalveolar lavage fluid and cultured isolates from nine inpatients, eight of whom had visited the Huanan seafood market in Wuhan. The ten genome sequences of 2019-nCoV from the nine patients shared ≥99·98% sequence identity. 2019-nCoV was closely related (88% identity) to two bat-derived severe acute respiratory syndrome (SARS)-like coronaviruses, bat-SL-CoVZC45 and bat-SL-CoVZXC21, collected in 2018 in Zhoushan, eastern China. However, it is more more distant from SARS-CoV (79%) and MERS-CoV (50% identity). Phylogenetic analyses demonstrated that 2019-nCoV falls within the subgenus Sarbecovirus of the genus Betacoronavirus, with a relatively long branch length to its closest relatives bat-SL-CoVZC45 and bat-SL-CoVZXC21. Homology modelling suggests that 2019-nCoV has a similar receptor-binding domain structure to that of SARS-CoV, despite amino acid variations at some key residues. Therefore 2019-nCoV can be considered to be a new human-infecting betacoronavirus. Bats may have been the original host of this virus but an animal sold at the seafood market in Wuhan may have been an intermediate host. Importantly, structural analysis suggests that 2019-nCoV may bind to the angiotensin-converting enzyme 2 receptor in humans.
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