Conceptual illustration of the upper part of an optical microscope penetrating a coronavirus capsid in order to examine its constituents. Different strains of coronavirus are responsible for diseases such as the common cold, gastroenteritis and SARS (severe acute respiratory syndrome). The new coronavirus SARS-CoV-2 (previously 2019-CoV) emerged in Wuhan, China, in December 2019. The virus causes a mild respiratory illness (Covid-19) that can develop into pneumonia and be fatal in some cases.