2019-nCoV and SARS-CoV seriously threatened human health. In order to know the genetic relations of the two dangerous clades and genetic mechanism of origin of 2019-nCoV, we compared whole genomic sequences of SARS-CoV and 2019-nCoV clades, and dissected phylogenetic histories of them. To our surprise, we found that the two clades may frequently exchange their genetic materials through homologous recombination in recent decades, resulting in 2019-nCoV and its sister branch represented by CoVZC45. Particularly the 2019-nCoV lineage might thereby acquire the receptor-binding domain from the SARS-CoV clade, enabling it to make use of angiotensin-converting enzyme 2 as well and thus spread rapidly in humans. Our findings suggest the accomplice role of a virus of SARS-CoV clade in COVID-19 and warn of the possible emergence of more mosaic CoVs capable of launching severe epidemic.

A novel bat coronavirus (2019-nCoV) caused an outbreak of infectious pneumonia termed COVID-19 in the world. This reminds us of another notorious bat coronavirus, SARS-CoV, which mysteriously broke out in China 17 years ago and killed nearly 800 people worldwide. A key to its efficient human attack is adopting angiotensin-converting enzyme 2 (ACE2) as the receptor. The relationship between 2019-nCoV and SARS-CoV has aroused much public concern. To our surprise, we found that the two CoV lineages may frequently exchange their genetic materials through homologous recombination. Particularly 2019-nCoV might thereby acquire the receptor-binding domain from the SARS-CoV clade, enabling it to make use of ACE2 as well and thus spread rapidly in humans. Our findings suggest the accomplice role of a virus of SARS-CoV clade in COVID-19 and warn of the possible emergence of more mosaic CoVs capable of launching severe epidemic.