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Covid-19 coronavirus particles, coloured scanning electron micrograph (SEM). Also called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), this virus causes the disease Covid-19. This sample was isolated from a patient in the USA. Virus particles are seen emerging from the surface of cells cultured in the laboratory. SARS-CoV-2 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 mid February 2020, over 70,000 have been infected in China with over 1700 deaths. (KEYSTONE/SCIENCE PHOTO LIBRARY/NIAID-RML/NATIONAL INSTITUTES OF HEALTH/SCIENCE PHOTO LIBRARY)