Covid-19 coronavirus binding to receptors, illustration. Molecular models of the spike proteins (red) for the Covid-19 coronavirus binding to receptors (blue) on the target cell. The receptor is an angiotensin-converting enzyme 2 (ACE2) type receptor, which is the entry route for all coronavirus particle types. Covid-19, which emerged in Wuhan, China, in December 2019, is a mild respiratory illness that can develop into pneumonia and be fatal in some cases. It is caused by the SARS-CoV-2 (previously 2019-nCoV) coronavirus. As of March 2020, the SARS-CoV-2 virus has spread to many countries worldwide and has been declared a pandemic. Over 200,000 have been infected with several thousand deaths.