COVID-19 is an infectious disease caused by SARS-CoV-2, which invades human cells through the ACE2 (angiotensin-converting enzyme 2) receptor (Atzrodt et al., 2020; Li et al., 2020a); it enters the body similarly to SARS-CoV and its clinical manifestations are similar to those of SARS-CoV (Shang et al., 2020; Huang et al., 2020b). Here, ACE2 is linked to COVID-19.