A Muslim pilgrim wears a mask as she walks to Mecca's Grand Mosque to perform evening prayers on October 8, 2013 prior to the start of the annual hajj pilgrimage which begins on October 13. More than two million Muslims have arrived in the holy city for the hajj, one of the world's largest human assemblies, amid concerns over the deadly MERS coronavirus. AFP PHOTO/FAYEZ NURELDINE (Photo credit should read FAYEZ NURELDINE/AFP/Getty Images)