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Coronavirus pandemic. Conceptual illustration of a coronavirus particle and a world map formed of people. Different strains of coronavirus are responsible for diseases such as the common cold, gastroenteritis and SARS (severe acute espiratory 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. The coronaviruses take their name from their crown (corona) of surface spike proteins (large protrusions), which are used to attach and penetrate their host cells. Also within the membrane are hemagglutinin-esterase glycoproteins (smaller protrusions), small envelope glycoproteins (holes) and membrane proteins (outlined on membrane surface). Image credits: ANDRZEJ WOJCICKI/Science Source (Unique ID: SS22566314). Image and text copyright © 2021 Science Source/Photo Researchers, Inc. All rights reserved.