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Coloured transmission electron micrograph (TEM) of SARS-CoV-2 coronavirus particles (round) isolated from a UK case of the disease Covid-19. SARS-CoV-2 (previously 2019-nCoV) was first identified in Wuhan, China, in December 2019. It is an enveloped RNA (ribonucleic acid) virus. The coronaviruses take their name from their crown (corona) of surface proteins, which are used to attach and penetrate their host cells. Covid-19 is a respiratory infection that can lead to fatal pneumonia. As of the 23rd March 2020, over 300,000 have been infected worldwide with over 14,500 deaths. Movement restrictions and infection control measures have been put in place to slow the spread of the virus. (KEYSTONE/SCIENCE PHOTO LIBRARY/NATIONAL INFECTION SERVICE / SCIENCE PHOTO LIBRARY)