Potential covid-19 treatment. Illustration of angiotensin-converting enzyme 2 (ACE2) molecules (red) in solution around SARS-CoV-2 coronavirus particles (yellow). This coronavirus, first identified in Wuhan, China, in December 2019, causes the respiratory disease covid-19. The virus infects human cells by its spike (S) protein (blue) attaching to ACE2 receptors on the cell surface. Soluble ACE2 could be used as a therapy to treat covid-19, the molecule would attach to the viral S proteins, preventing them from attaching to and infecting cells.