Fig. 1.

Zoonosis of corona viruses. Bats are the primary reservoirs for the three zoonotic corona viruses, SARS-CoV, SARS-CoV-2 and MERS-CoV. Human transmissions often occur through intermediate hosts. Civets and dromedary camels serve as intermediate hosts for SARS-CoV and MERS-CoV, respectively while intermediate host for SARS-CoV-2 is yet to be confirmed but are anticipated to be pangolins. For cellular entry, the receptor binding domain (RBM) of SARS-CoV S protein interacts with the host ACE2 receptor. SARS-CoV-2 also utilizes the same RBM-ACE2 receptor interaction but possesses a greater binding affinity compared to SARS-CoV. The entry of MERS-CoV is mediated by the interaction of RBM with the host receptor DPP4.