As millions of Muslim pilgrims prepare to converge on holy sites in Saudi Arabia this [northern] autumn, the global health community is anxiously monitoring an outbreak of a respiratory virus known as Mers.
The Middle East respiratory syndrome coronavirus has infected at least 77 people, killing 42. Sixty-two of those infected became ill in Saudi Arabia, with 36 deaths.
Could the pilgrimage to Saudi Arabia, as vast crowds from around the world gather at holy sites in Mecca and elsewhere, trigger a wider global outbreak, echoing the severe acute respiratory syndrome (Sars) epidemic that swept the world a decade ago?
This alarming possibility was explored in a recent foreign policy piece by Laurie Garrett, whose The Coming Plague: Newly Emerging Diseases in a World Out of Balance, published in 1994, is prescient.
Mecca's Kaaba, writes Garrett, could be "a massive petri dish".
The Mers outbreak, identified in Jordan last year, has yet to assume the awful dimensions of Sars, another coronavirus. First detected in China in 2002, Sars went global, raising fears of a pandemic.
It infected more than 8000 people, killing 774 by July 2003.
The new virus is transmitted by close human contact from aerosol droplets. Mers is lethal, with a 55 per cent fatality rate. By comparison, Sars had a 9.6 per cent mortality rate.
Mers, which has a short life outside the host, causes fever, coughing and breathing problems, triggering pneumonia and kidney failure.
The World Health Organisation and the United States Centres for Disease Control are monitoring the outbreak. No vaccine exists. While no quarantine measures are in force, nor travel advisories issued, the Saudis are limiting pilgrim visa numbers.
But millions of workers travel to and from the Saudi kingdom, heightening concerns.
Maybe thinking of the thousands of American Muslims expected to visit Saudi Arabia, the CDC "recognises the potential for the virus to spread further and cause more cases and clusters globally, including in the United States."
Dr David Swerdlow, the CDC's point man on Mers, says airlines are consulted and US border staff provide fact cards to travellers from areas where Mers has surfaced.
Jordan, Saudi Arabia, Tunisia, Qatar, the United Arab Emirates, France, Germany, Italy and Britain all have cases.
The Syrian civil war has also raised fears of a spreading pestilence. In an email to the Herald, Garrett says that while the WHO advisory is "pertinent to real hospitals and medical centres, nobody holds out much optimism should Mers hit refugees or internally displaced Syrians".
Camps exist in Turkey, Jordan, Iraq and Lebanon. A UN report in April cited serious health concerns.
Meanwhile, scientists have fully sequenced the Mers genome, comparing it with Sars strains and other coronaviruses. "The virus genome is similar, but not the same, as the coronavirus in bats," says Swerdlow. A New England Journal of Medicine study says incubation is 5.2 days. The CDC recommends 12 days to be safe.
A scientific team is testing Saudi Arabian bats, often linked to zoonotic diseases, as well as cats, sheep, goats and camels, which may be intermediate hosts between bats and humans for Mers.
"Right now, at the scientific level, it's interesting that a new coronavirus has emerged from a potential bat reservoir and that it has such a high mortality rate," says Matthew Frieman, a virologist with the University of Maryland School of Medicine.
This animal-to-human scenario remains a hypothesis, but Sars jumped from bats to humans, either directly or via civets sold as food in markets.
Finding the reservoir is key to controlling Mers.
The first victim, a Jordanian man, was identified in April last year. Scientists do not believe the Jordanian infected everyone else. Which means, says Frieman, multiple infections may be linked to the same reservoir.
Once civets were identified in the Sars outbreak, culls, plus quarantining victims, effectively stopped the virus in its tracks.
In many ways Mers has piggybacked globalisation and quickly spread in its dormant stage by unwitting air passengers. It may also have benefited from other world out-of-whack developments, such as habitat loss - which makes animal-to-human transmission more likely - rapid urbanisation, population growth and climate change.
Happily, coronaviruses are in a family that don't mutate as much as, say, influenza, which may make it easier to find a vaccine.
"The problem is it takes a long time to find a vaccine," says Frieman. "The saving grace at the moment is that the transmission rate is very, very low. The probability of spreading from one person to another is really low unless you have close contact."
Infection "clusters" have been reported in Saudi Arabia, France and Jordan. The New England Journal of Medicine found that 21 out of 23 Saudi Arabia cases contacted Mers via person-to-person transmission at three medical facilities.
People suffering from other ailments, such as heart disease or diabetes, may be more susceptible.
"Almost everyone who has had a lethal infection has been immune-compromised in some way," says Frieman. "But, again, the fatality rate is over 50 per cent. So it's really something to worry about."
There is much to worry about in a global petri dish, but Sars gave epidemiologists a decade to prepare for whatever happens next.
"Even if Mers disappears, and there are no more cases ever, it shows that the continued spread, and spillover, of viruses from an animal reservoir, like bats, is only going to happen more frequently," says Frieman. "Whether it's coronaviruses or something else next time, we are developing the ability to react very quickly. That's really important for our global response."
Garrett says that when she wrote The Coming Plague "most physicians scoffed at the idea of outbreaks in wealthy countries", while links between globalisation and outbreaks were controversial.
No longer. Billions have been spent on vaccines, medical tools and surveillance. International health regulations, passed by the World Health Assembly in 2005, make it obligatory "to report outbreaks ... and share viral and bacterial samples", says Garrett.
Yet poor grassroots health care is a weak point. Garrett offers a chilling scenario. A pilgrim family visit Saudi Arabia, then fly home to a nation with poor heath care, say Somalia or Pakistan. When a family member succumbs to "something like flu" he or she is nursed at home before being hospitalised with pneumonia. Other family members become ill.
"How long would it take before health authorities connect the dots, see an outbreak, realise the family has been to Saudi Arabia, and send samples to WHO for Mers analysis?"
It is in such vacuums that pandemics are born.
Global spread biggest fear
What is this new threat?
The new virus is a type of coronavirus, a large family of viruses which includes the common cold and Sars, and causes respiratory infections in humans and animals. Patients present with fever, cough and breathing difficulties. It causes pneumonia and, sometimes, kidney failure. Most people infected so far have been older men, often with other medical conditions. The name comes from the crown-like spikes that cover the virus' surface.
How is it spread?
It's unclear, but infected people may spread it in droplets when they cough or sneeze. The fact close contacts appear to have been infectious suggests the virus has limited ability to pass from person to person.
How dangerous is it?
Based on the number of cases, experts believe the new virus is not very contagious. But the global concern is about its potential to spread far and wide.
Can it be treated?
Doctors don't yet know what the best treatment is, but people with severe symptoms need intensive medical care to help them breath. There is no vaccine.
What should I do to protect myself?
Some general measures may help prevent its spread - avoid close contact, when possible, with anyone who shows symptoms of illness (coughing and sneezing) and maintain good hand hygiene.