ACE2 and severe acute respiratory syndrome: Different studies have proven that the affinity between the viral RBD and host ACE2 in the initial SARS-CoV attachment step can determine if a host is susceptible to SARS-CoV infection (Li et al., 2004; Li et al., 2005a; Li et al., 2005b; Li et al., 2005c; McCray et al., 2007).