Coronaviruses (CoVs), which are enveloped, positive-sense, single-stranded RNA viruses of zoonotic origin and belong to the family Coronaviridae in the order Nidovirales, are divided into four genera: alpha, beta, delta and gamma coronavirus. The emerging CoVs, including severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), both belonging to beta coronavirus, have caused recent pandemics of respiratory infectious diseases with high mortality.