Human ACE2 receptor, computer illustration. 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.