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MERS coronavirus proteins. Cutaway computer model showing the protein structure of a MERS coronavirus particle (virion). MERS (Middle East respiratory syndrome) is a viral respiratory illness caused by the MERS-associated coronavirus (MERS-CoV); a single stranded RNA (ribonucleic acid, blue coil) virus. Each MERS-CoV virion is made up of four major structural proteins: nucleocapsid, spike trimer (red), membrane (yellow) and envelope (purple), plus HE haemagglutinin-esterase dimer (orange). This new virus, which first emerged in 2012, is being tracked by the World Health Organisation (WHO), with 53 confirmed cases and 30 deaths as of early June 2013. (KEYSTONE/SCIENCE PHOTO LIBRARY/RAMON ANDRADE 3DCIENCIA/SCIENCE PHOTO LIBRARY)