Coronavirus is a single strand positive RNA (+ssRNA) virus, belonging to order Nidovirales, family Coronaviridae, and subfamily Orthocoronavirinae [13]. According to the characteristics of serotype and genome, the coronavirus subfamily is divided into four genera: α, β, γ, and δ [14]. There are six kinds of coronaviruses known to infect humans, including 229E and NL63 of α genus [15,16], OC43, HKU1, Middle East respiratory syndrome-associated coronavirus (MERSr-CoV), and severe acute respiratory syndrome-associated coronavirus (SARSr-CoV) of β genus [16,17]. The coronavirus isolated from the lower respiratory tract of patients with unidentified pneumonia in Wuhan is a new type of coronavirus (SARS-CoV-2) belonging to genus β, and subgenus sarbe [5]. SARS-CoV-2 is different from the zoonotic MERSr-CoV and SARSr-CoV and becomes the seventh coronavirus to infect humans [5]. The phylogenetic analysis of the coronaviruses based on full-length genome sequences shows that SARS-CoV-2 has the smallest genetic distance from bat coronavirus, but only about 45%–90% similarity with SARSr-CoV, and a lower similarity of 20%–60% with MERSr-CoV [18]. Therefore, a bat is probably the original host of SARS-CoV-2, although the intermediate host may still exist in the process of transmission from bats to human beings.