ACE2 and infection: Based on the knowledge about this specific viral infection and considering the prolonged viral RNA detection in anal swabs [34] and detectable viral RNA in the blood cohort progressing to a severe symptom stage [35], we proposed the potential infection course of SARS-CoV-2 as follows (Figure 3): upper respiratory infection (mainly by respiratory droplets); lower respiratory infection (mainly presented as pulmonary infection); viremia formation; and transmission to other organs (including the GI tract) and colonization via ACE2.