“LET’S hope this bug doesn’t make it to Mecca.” The bug in question is MERS, the coronavirus that emerged last year in the Arabian Peninsula. Ron Fouchier of Erasmus Medical Center in Rotterdam, the Netherlands, has good reason to be concerned. The virus has so far infected more than 40 people, some of whom haven’t apparently been in contact with an infected person or animal. In an epidemiological analysis, the World Health Organization concludes that this means there could be many mild, unrecognised cases spreading the virus in the general population. This week Tunisia’s health ministry announced that a 66-year-old man had died and his two sons were ill with MERS after returning from Saudi Arabia and Qatar. They’d had no contact with known cases. There are fears that pilgrimages to Saudi Arabia, scheduled for July and October, could spread any virus carried in the population. This article appeared in print under the headline “Is MERS on the loose?