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Covid-19 coronavirus sample. Coloured transmission electron micrograph (TEM) of SARS-CoV-2 coronavirus particles (blue) isolated from the first US 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 late February 2020, around 80,000 have been infected in China with over 2600 deaths. There have been over 2000 confirmed cases outside of China, with 27 deaths outside mainland China. In China and elsewhere travel restrictions and infection control measures have been put in place to slow the spread of the virus. (KEYSTONE/SCIENCE PHOTO LIBRARY/CDC/SCIENCE PHOTO LIBRARY)