ACE2 and infection: In addition to the respiratory system, the gastrointestinal tract is a major infection site of SARS-CoV-2, as ACE2 is highly expressed in proximal and distal enterocytes (16) and viral nucleocapsid protein has been visualized in the cytoplasm of gastric, duodenal, and rectum glandular epithelial cells from a COVID-19 patient (17).