The results clearly show that the circulating virus in Saudi Arabia is centred around Riyadh, with sporadic excursions to other centres, although additional virus genomes will need to be analysed to more firmly establish the locations involved.
The researchers' analysis of how quickly the virus has evolved, and how it has transmitted between locations and patients, suggests that a single transmission from animal to human is unlikely. Instead, it appears that the virus has transmitted from an animal reservoir to humans on several occasions, as well as transmitting between humans.
Diverse genetic variants of the virus have appeared in Riyadh, and this high local diversity might indicate that the virus is being transmitted from an animal reservoir which is being continuously imported from other regions. Alternatively, it may be down to the fact that Riyadh is the region's largest population centre, and therefore the largest target for human-to-human transmission of the virus.
The results also show that considerable time has passed since the viruses analysed in this study shared a common ancestor, which lends support to the idea that MERS-CoV might be being transmitted to humans by an intermediary animal host. While an ancestor of the virus has been found in bats, and signs of the virus have been found in dromedary camels, no animal reservoir for the virus has yet been definitively identified, and the authors reiterate an urgent need for further animal studies in the region to better establish where the virus is coming from.