Covid-19 coronavirus particles. Coloured scanning electron micrograph (SEM) of SARS-CoV-2 coronavirus particles (green) on a cultured cell (VERO E6, blue) developed from a patient sample. SARS-CoV-2 (previously 2019-nCoV) was first identified in Wuhan, China, in December 2019, and has been declared a pandemic. It is an enveloped RNA (ribonucleic acid) virus. It causes Covid-19, a respiratory infection that can lead to fatal pneumonia. As of March 2020, over 200,000 have been infected worldwide with thousands of deaths. Social restrictions and infection control measures have been put in place to slow the spread of the virus. This sample was imaged at the NIAID (National Institute of Allergy and Infectious Diseases) Integrated Research Facility (IRF) in Fort Detrick, Maryland, USA.