Millions of Muslim pilgrims are in Saudi Arabia for the Hajj. This year health officials are taking extra precautions because of Middle East Respiratory Syndrome (MERS).
For the coming days millions of pilgrims will live, travel, and perform their religious rituals in crowded areas, a situation where diseases often spread easily.
Part of the problem with MERS is that the World Health Organisation has what it calls only "very limited information" on how it spreads.
Al Jazeera's Hashem Ahelbarra reports from Mecca.