Little is known about the new pathogen, beyond the fact that it can be lethal by causing respiratory problems, pneumonia and kidney failure. It can be transmitted between humans, but unlike its cousin, the SARS virus, which sparked a scare a decade ago, it does not seem very contagious.
Even so, for any respiratory virus the mass gathering of the Hajj provides a perfect opportunity to first spread at the two holiest Muslim shrines in the cities of Makkah and Medina, and then travel around the globe at jet speed as pilgrims return home.
The 2012 Hajj drew 3.1 million people – and this year's event likewise occurs in October, as the northern hemisphere slides into the season for coughs and sneezes.
UN World Health Organisation (WHO) head Margaret Chan sounded the alarm to ministers at the agency's annual congress in May.
"We need to get the facts clear and get the appropriate advice to all your countries where your pilgrims want to go to Makkah. It is something quite urgent," she said.
Experts point first and foremost to figuring out the basics of the Middle East Respiratory Syndrome (MERS) coronavirus.
Is it transmitted by contact – if a patient contaminates his home or workplace with droplets containing virus? Or is it done by breathing in virus from coughs and sneezes? What is the best treatment for it? What about a vaccine? Are there risks of viral mutation? And is there an animal host which acts as a reservoir for the virus?
The first recorded MERS death was in June 2012 in Saudi Arabia. The count has ticked up steadily, with a flurry this May and June taking it to 77, the bulk of them in the kingdom.
Forty MERS patients have died to date, an extremely high rate of 52 percent, compared to nine per cent of the 8,273 recorded patients with SARS, which was centred on Asia.
But again, the tally of people who have fallen ill with MERS but not been diagnosed with it, or who may have been infected but not developed symptoms, is simply unknown.
As the fight for knowledge unfolds behind lab doors, the WHO is urging nations to monitor respiratory infections, especially among patients returning from the Middle East, but has held off calling for travel restrictions.
"This is really a new phenomenon that we're dealing with," Keiji Fukuda, WHO assistant director general for health security, told the International Conference on Prevention and Infection Control in Geneva this week.
"We don't know what the potential is yet, based on the information we have, for sustained human-to-human transmission. We don't know what the full geographic extent of this virus is right now."
Leading virologist Laurent Kaiser of the Geneva University Hospitals told AFP: "It's really a balance between too much precaution and no precaution. At this time, we have to be worried, we have to be careful."
While MERS centres on Saudi Arabia, there have been laboratory-confirmed cases originating in Jordan, Qatar and the United Arab Emirates.
Britain, France, Germany, Italy and Tunisia have had cases who were either sent there for care or who fell ill after returning from the Middle East. France, Italy, Tunisia and Britain have also seen limited transmission among patients who had not been to the Middle East but had close contact with people who had.
So far, MERS has essentially been found in nations with health services capable of tracing and tackling such diseases. But the Hajj draws a broad spectrum of Muslims, including from poor countries which struggle to cope even with commonplace diseases.
"We don't know if the disease is there right now. They don't have surveillance," Saudi Arabia's deputy health minister, Ziad Memish, told AFP on the sidelines of the Geneva conference.
Health experts give praise to Saudi authorities for beefing up vigilance for infectious diseases over the years.
They also note that the Hajj has successfully ridden out two previous viral episodes in the past decade – SARS in 2003 and H1N1 influenza in 2009, although the difference now is that Saudi Arabia is the apparent hotbed of MERS.
Memish, who is also a medical professor and runs a WHO-accredited research centre on the medicine of mass gatherings, pointed to the success of lower-scale umrah pilgrimages to Saudi Arabia this year.
"I think it's comforting that as of today, four and a half million people have performed the umrah in Makkah and nothing has happened," Memish said. "But of course we're making all the arrangements and all the planning to do active surveillance, to be able to intervene."
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The story is complete rubbish to discourage the migration out of Europe as the powers want them to stay in Europe.
This is very important. My uncle came on Hajj and had got a disease that let him weak and in bed for weeks. When you are close proximity to people from many countries it is easy catch infections.
It is surprising that so many are thinking of Saudi SARS in terms of a potential pandemic virus - it simply does not fulfill all the criteria. Specifically although novel it is clearly not particularly contagious. Two aspects are of particular concern; we have had no success with vaccines for coronaviruses (there isn't one for Hong Kong SARS) and early research found this virus to be 'unique'(sic) in being able to grow in the cells of multiple species. Ergo the greatest risk would appear to be that - carried worldwide by pilgrims to Mecca - it becomes endemic and ineradicable. Last October the Hajj went ahead as usual with no precautions whilst the world was distracted by Storm Sandy. We may have 'ducked that bullet' but as the virus is clearly widespread we cannot expect to a second time! The obvious steps to take are that Muslim communities everywhere are discouraged from choosing to do their once in a lifetime Hajj until we know enough to appraise the risks and the few who feel that they must - because of age - are quarantined and monitored on their return. It is not virologists who should determine policy on this but those responsible for national/homeland security! Finally some thought should surely be given to the social/political fallout if these precautions were not taken and Saudi SARS became a deadly endemic disease? First Muslims would be seen as 'plague carriers' clearly responsible for introducing the disease with all that that might entail (hence the importance of being seen to dissuade as many as possible from going this October)and second it would not be safe to assume that the victims in the USA would be elderly men. This is perhaps the most puzzling feature of both Saudi SARS and variant H7N9 in China - the clear sex bias of fatalities and cases and the singular lack of attention as to what the explanation might be! If Occam's razor deters us from hypothesizing about sex-linked viruses then the explanation will probably lie in basic epidemiology. I therefore offer a statistician's perspective and a hypothesis that can easily be falsified on Popperian logic. Older Arab males and older (urban) Chinese males have something in common statistically; older males in both countries are noted for being heavy smokers – inhaling deeply and coughing vigorously - yet no data on the smoking status of cases – the easiest and cheapest data to collate surely? - have been divulged. If this were to be the route by which people become infected it would make sense that distressed female relatives would also inhale deeply in the environs of virus particles. However in Western countries those who inhale deeply are more likely to be young sports men and women and young people at outdoor gigs being 'energetic' in close proximity so it would not be safe to make any assumptions given that this behaviour simply does not exist in Saudi Arabia! Pandemics are all over inside 12 months usually but if Saudi SARS is allowed to become endemic the repercussions could be more like AIDS than Influenza...