Virus infection is mediated by the virus envelope spike glycoprotein that is composed of two subunits (S1, S2) that bind to its receptor, the host cell angiotensin-converting enzyme 2 (ACE-2), an enzyme responsible for blood pressure control and located abundantly on nasal, pulmonary alveolar, and intestinal epithelial cell membranes. Here, ACE2 is linked to viral infectious disease.