ACE2 and infection: SARS-CoV-2 enters the respiratory tract via the nose and causes an infection through a series of events including binding to the nasal epithelial cells, entering the nasal epithelial cells via the host receptor angiotensin-converting enzyme-2 (ACE-2), undergoing local replication and transmission after entry, as well as causing the infection of ciliated cells in the upper respiratory tract [6].