Health officials in Saudi Arabia have asked pilgrims visiting its holy sites to wear masks in crowded places to stop the spread of the MERS coronavirus.A list of requirements issued by the health ministry also tells elderly people or those with chronic diseases to postpone their pilgrimage.Thirty-eight people have died from the virus in Saudi Arabia.Millions of Muslims from around the world are expected to take part in the Hajj this October.Once a year, pilgrims make the journey to Mecca in Saudi Arabia and pray together before the Kaaba.Muslims also travel to the site at other times, as well as visiting the Masjid Al-Nabawi, or Mosque of the Prophet, in Medina.Health officials urged people taking part to maintain personal hygiene standards, use a tissue when sneezing and coughing, and have the necessary vaccinations.The MERS (Middle East respiratory-syndrome) coronavirus emerged in the Arabian peninsula in September 2012 and is part of a large family of viruses, which includes the common cold and Sars (severe acute respiratory syndrome).The World Health Organization has so far confirmed of a total of 80 cases of infection, including 44 deaths worldwide.Saudi Arabia introduced requirements for polio immunisation certificates in 2003 after fears of a resurgence of the virus.