Spread of MERS interactive As of May 9, the World Health Organization reported 536 diagnosed cases of MERS, among them 145 deaths. Saudi Arabia 346 cases (74 deaths) United Arab Emirates 47 cases (5 deaths) Qatar 7 cases (4 deaths) United Kingdom 4 cases (3 deaths) Oman 4 cases (4 deaths) Italy 3 cases Jordan 3 cases (3 deaths) Kuwait 3 cases (1 death) Tunisia 3 cases (1 death) France 2 cases (1 death) Germany 2 cases (1 death) United States 2 cases Malaysia 1 case (1 death) Philippines 1 case Greece 1 case Egypt 1 case Yemen 1 case Saudi Arabia 346 cases (74 deaths) United Arab Emirates 47 cases (5 deaths) Qatar 7 cases (4 deaths) United Kingdom 4 cases (3 deaths) Oman 4 cases (4 deaths) Italy 3 cases Jordan 3 cases (3 deaths) Kuwait 3 cases (1 death) Tunisia 3 cases (1 death) France 2 cases (1 death) Germany 2 cases (1 death) United States 2 cases Malaysia 1 case (1 death) Philippines 1 case Greece 1 case Egypt 1 case Yemen 1 case 2012 2013 2014 Diagnosed cases Deaths Circles are sized based on the number of cases and centered in the country. Graphics by Xaquín G.V., Ryan Morris, Kelsey Nowakowski, and John Tomanio, NG Staff

The map displays only those cases for which individual patient data can be tracked. Sources: Andrew Rambaut and Paul Wikramaratna, University of Edinburgh; World Health Organization; European Centre for Disease Prevention and Control.

The Index Patient

His name, two years later, is guarded within the privacy of medical files and a family compound of bereaved relatives, his wives, and his children. He was 60 years old. He was a businessman. He lived in Bishah, a small city southeast of the great Saudi port metropolis of Jeddah, and when he became too sick for the Bishah doctors to care for him properly, he was transported to Jeddah, feverish and coughing. There he lay, inside one of the tall white buildings of the Dr. Soliman Fakeeh Hospital, where a diagnostic physician called onto his case happened to be a virology specialist, an Egyptian physician named Ali Mohamed Zaki, who liked to pay close attention to the latest reports of pernicious infectious disease.

All this was at the very beginning, a single week in the middle of June 2012, long before the sick man was understood to be the "index patient."

In clinical reports you don't see the popularized term "patient zero." Once the international detective hunt was under way, as one researcher after another joined in and the search and the connector clues spread around the globe—to Rotterdam and New York City, to the Spanish Canary Islands and Oman and Qatar, to France, England, Greece, Jordan, Egypt, Nigeria, Hong Kong, Malaysia, Australia, Indiana, and, just announced this past week, Florida—and as the questions and implications continue to spread, the man from Bishah has invariably been referred to as the "index patient" or "the patient in Jeddah."

He died in the hospital, 11 days after he was brought in. Zaki says the work on the Bishah man was routine at first, distressing but routine. The patient developed pneumonia, his kidneys began to fail, and Zaki sent sputum samples to the Saudi Ministry of Health, as required by law in such cases, to check for swine flu.

Negative for swine flu. Zaki wondered about hantavirus, which is carried by rodents and can be deadly in humans; when he studied the patient's samples under a microscope he could see the kinds of changes that told him a virus was at work. But no. Negative for hantavirus. Zaki was perplexed, and growing frustrated. He began to guess that the patient had some form of what are called paramyxoviruses—the family that includes measles and mumps. In the 1990s there were scary, lethal eruptions of new paramyxoviruses: in Australia, where the victims were stabled horses and two humans who cared for them up close, and in Malaysia, where a paramyxovirus named Nipah killed more than a hundred people and brought about the slaughter of more than a million pigs.

It didn't seem to be a paramyxovirus, either; Zaki had the lab capabilities to test for that. By the closing days of June 2012 the man from Bishah was deceased, his mourning relatives had come and and gone, and Zaki was not letting go. Maybe his paramyxovirus testing needed another round? As he told me last week, by phone from his current office at the medical school of Ain Shams University in Cairo, "I wanted to know what this is." Some viral malady had felled that patient, something different from anything Zaki could recognize, and apparently something fatal.

So Zaki put some of the samples he had saved from the Bishah man into sterile plastic tubes. He double tubed them for safety, set them inside a metal biohazard box, and shipped the box by courier to Rotterdam, where an institute called the Erasmus MC employs some of the most celebrated virus detectives in the world.

And that was how it started.

View Images A Bedouin in western Abu Dhabi, United Arab Emirates, caresses his camels, which have been brought from Saudi Arabia for a beauty contest. The discovery that many camels show current or past infection with the MERS virus has sent shock waves throughout the Middle East, where camels are revered as important sources of transport, food, entertainment, and affection. PHOTOGRAPH BY DAVID YODER, NATIONAL GEOGRAPHIC SOCIETY/CORBIS

The Bat Man

Three months later, and halfway around the planet, a 3 a.m. telephone call in New York City woke a veterinary epidemiologist named Jonathan Epstein. The research organization Epstein works for, EcoHealth Alliance, studies global infection and disease outbreaks, especially those called zoonotic, meaning they are caused by pathogens—malevolent tiny organisms—that have "spilled over," as National Geographic contributing writer David Quammen explained in his recent book about these outbreaks, from nonhuman animals to people. The EcoHealth scientists frequently work alongside a Columbia University team led by molecular biologist and epidemiology professor named Ian Lipkin, whose Center for Infection and Immunity laboratory at Columbia is another world center of pathogen discovery and viral research.

Epstein, to put it unscientifically, is a bat man. Bats were not his initial career specialty, but for many reasons the flying, excreting, fantastically multispecies, globally adaptable bat turns out to be a superior biological starting place for some of the meanest pathogens implicated in zoonotic disease. Epstein and Lipkin had both worked intensely during the international effort to understand and contain SARS, Severe Acute Respiratory Syndrome, which killed nearly 800 people in a global epidemic in 2003. SARS began in China, and for a time it was thought that people were contracting it from the little Chinese animal called the civet. That proved to be wrong: The animal sources of the SARS virus, Epstein and his fellow researchers had figured out, were bats.

The particular family to which the SARS virus belongs has a visually descriptive name: coronaviruses. The "coronas" are knobby rings on each viral particle, which makes the viruses look a bit like crowns; that's what "corona" means in Latin. There's nothing inherently scary about coronaviruses in humans; people pick them up all the time, label them colds, and recover without incident. But SARS-CoV, as it is formally called, was the first coronavirus known to have wrought terrible damage among people it infected. Unlike the common cold, SARS killed a lot of people. It spread easily enough that more than 8,000 individuals were diagnosed with SARS before the 2003 epidemic was brought to a halt, and had it been more contagious, its toll would have been far higher.

And now Lipkin was calling Epstein in the middle of the night because Lipkin had just gotten off the phone with the Saudi Ministry of Health, which was asking for help. Something that looked like SARS-CoV but wasn't—a whole new kind of coronavirus—had been identified in the sputum of the patient from Bishah.

Zaki had suspected as much from a preliminary test he ran himself, and the Rotterdam scientists had confirmed it. Mystery samples arrive at Erasmus every week from all over the world, usually attached to a clinician's plea for enlightenment. Why did this patient die? What is killing these animals? Why don't we understand this? Even so, the lone shipment from Jeddah had stirred enough curiosity at Erasmus to set off a full sequence of lab tests.

The Egyptian doctor was right: It wasn't something familiar. It was a "previously unknown coronavirus," as Zaki and the Rotterdam researchers would call it in their New England Journal of Medicine report and although this new virus did not appear nearly as worrisome as SARS—not yet, anyway—the SARS epidemic had taught the world how crucial it was to move quickly on a warning signal like this.

So it was that Lipkin, Epstein, an EcoHealth disease ecologist named Kevin Olival, and a band of scientists and translators from the Saudi Ministry of Health arrived a few days later at the small airport in Bishah. They came in two waves, Olival following Epstein by a day, each group of foreigners loaded down with odd-shaped luggage: big boxes; massive duffles full of respirators, protective suits, gloves, nets, and syringes; and ten-foot-long cylinder cases carrying a technical device that bears an unfortunate glancing resemblance, as Olival says, to a giant bazooka. Harp traps, these are called. Like much of the apparatus the Americans brought with them, harp traps are used for catching bats.

Was it bats? SARS was carried by bats, and this new virus had many similarities to the one that causes SARS, but at this point the scientists could only speculate. Epstein had stared out the airplane window on the local flight from Riyadh, Saudi Arabia's capital, studying long stretches of desert broken by small patches of green—oases, irrigated crops, date farms. "I'm thinking, What kind of diversity of bats are we going to find in this town?" he told me. Assuming this virus was coming from animals, the "reservoir"—as scientists call the living being that hosts the virus before it makes the jump into humans—could be anywhere.

They'd packed whatever they could think of before they left, including extra-large needles, for example, for drawing blood from livestock. What was the obvious livestock of southwestern Saudi Arabia? "Sheep, goats, cows," Kevin Olival says. "Camels. I remember Jon and I brushing up on how you collect specimens from camels."

Out they all drove, from the Bishah hospital that had welcomed them, past the city shops and restaurants and auto dealers, and on to the residential neighborhood where the patient's survivors lived. There were multiple households to visit—in the Islamically acceptable manner, the late patient had had several wives. All the homes were clean inside, no obvious sign of bats. But bats usually aren't obvious. They hide by day, and it is their nature to secrete themselves in places where humans don't go. The team peered into corners and crevasses, looking for bat feces, which are as tiny as mouse droppings.

No bat trove. "We did a lot of just—ground sleuthing," Epstein says. They learned that the man from Bishah had a business outside town, where there was a warehouse, so they moved the sleuthing farther afield. Palm trees, wells, livestock—the researchers were extracting what they could from whatever livestock they could get to, swabbing and syringing. Some goats. Some sheep. Some camels. And there was this observation, perhaps not significant, but one that stuck in everybody's minds: At home in Bishah, in a paddock beside his family's homes, the index patient—though that was not yet his nickname—kept four camels that had no practical purpose except to live nearby. They were pets.

View Images Saudi men slaughter a camel for the 2012 Muslim celebration of Id al-Adha, the end of the annual pilgrimage to Mecca. Scientists know the MERS virus has infected many camels, but they don't yet know how—or even whether—camels are transferring the virus to humans. The Saudi health ministry has warned citizens to avoid eating raw camel meat and unpasteurized camel milk, and to stay away from sick camels. PHOTOGRAPH BY FAHAD SHADEED, REUTERS/CORBIS

Hidden Roosts

"The urgency was, this was potentially like SARS again, happening in the Middle East," Jon Epstein says now, which was why he, Olival, and two veterinarians from the Ministry of Health were sitting up late at night outside Bishah, Saudi Arabia, trying to figure out where the bats were coming from. The men could see them, small shadows darting around overhead after dark, but they hadn't been able to find the roosts.

Whatever this virus was, only one person had died of it, as far as anybody knew. By late September 2012 a Qatari man who'd been in Saudi Arabia had turned up sick in London with what was found to be a matching virus; that patient was still alive. But if the virus acted like SARS-CoV, if it was as contagious and perhaps even deadlier, then, as Epstein puts it, "this was a big deal."

That's why he so badly wanted to locate bats. They began driving from one small town to another, inquiring about bats, asking which buildings had been abandoned, until the break finally came: Check on my family's ancestral property, someone said; there are old buildings, built in the traditional dried-mud fashion, long since uninhabited. And in one of those buildings, peering into an underground room into which no human appeared to have ventured for many decades, Epstein saw—just long enough to get excited, before retreating hastily for the respirator and the hazmat suit—a colony, hanging out in the gloom, of some 500 roosting bats.

Now the trapping began. Not lethal trapping; these virus hunters have learned how to get what they need from an animal by annoying it rather than zapping its mortal coil. After five days of weighing, throat swabbing, measuring, pulling bits of wing membrane, and gathering fecal pellets—first within that initial colony and then in others they found later—the group had collected samples from almost a hundred bats, representing seven species. Those samples went straight to New York, where Lipkin and his fellow researchers worked them up—"around the clock, literally day and night," Epstein says.

The Camels

The virus that killed the man from Bishah still lacked a name. The World Health Organization (WHO), in dispatches that were brisk at first and then began to increase in length and urgency, spent the fall of 2012 calling it "novel coronavirus." In its December dispatch that year, the WHO tabulations mounted; five cases confirmed in Saudi Arabia, two in Qatar, two in Jordan. Both the Jordan patients were confirmed posthumously, from fluid samples kept in storage. They had died in April, before the man from Bishah, during what was described at the time as a brief pneumonia outbreak among some health care workers in Amman.

By the end of May 2013, 44 cases had been diagnosed, half of them fatal. The patients were feverish, hemorrhaging, kidneys failing, unable to breathe. Confirmations of the virus had turned up in England, Germany, and France; all the European patients had, as the WHO notification put it, "direct or indirect connection to the Middle East," which meant, in the case of the French patients, that the first diagnosed man had recently been on vacation in Dubai and that the second diagnosed man had shared the first man's hospital room.

The virus, it seemed, was able to pass from human to human. But why was it showing up now? And where had it started? If it was a zoonotic disease, like SARS—if it originated in bats, like SARS—then were the bats getting directly to the humans, or was there something else in between?

This is where the camels come in.

? NGM graphic. SOURCE: ministry of health, kindom of saudi arabia; world health organization Female 74 Another family member, a 47-year-old male died as well. He infected four others, including a 74-year-old female who later died. The owner exhibited MERS symptoms three days later, and died nine days after that. Five family members became infected; one, a 79-year-old female, died 16 days after the owner’s death. On August 5, 2013, a sick camel was treated and later sold by its owner, a 38-year-old Saudi Arabian man. Camels are suspected of transmitting the MERS virus to humans. How one cluster formed Male 47 Male age 38 died Female 79

Pathogens relocating from animals to people sometimes make lingering stops en route. A species of bat that's been carrying a virus for many bat generations, for example, may find itself newly confronted by humans, making direct contact likelier: a scratch, a bite, an altered living situation that drops virus-laden excretions into food or sleeping areas. In much the same way, the bat can also accidentally deliver a virus to an intermediate host, a different species of animal. The intermediate host may be perfectly comfortable having that virus on board; this new animal might or might not show any signs of viral illness at all. But it may live among people upon whose systems the virus wreaks awful havoc once it finds its way in.

In Rotterdam, the Erasmus researchers were deeply interested in this possibility. Whatever the virus was, it was working its most visible damage upon Saudi Arabia and the nations nearby. Its name, settled upon in May 2013 by the international committee in charge of naming new viruses (yes, alarmingly, there is such a thing), was now Middle East Respiratory Syndrome Coronavirus, shorthanded to MERS-CoV. "We said, 'What could be an intermediate host?'" recalls Erasmus virologist Bart Haagmans. Livestock seemed an obvious possibility. But livestock of the Middle East, right? "We thought, sheep. Cows. Goats. Camels."

Even when they're not present and active, viruses leave footprints inside the animals they pass through: antibodies, which scientists can spot and identify long after the virus itself has checked out. Like other such detectives around the world, the Erasmus scientists would do their hunting by studying sera—various animals' collected blood fluids. But they needed sera for comparison purposes, from animals that had never encountered this MERS-CoV, in order to conduct proper studies of possible intermediate hosts in the Middle East. So they began gathering up control sera. Some would plainly be easy to find; in the Netherlands, where they assumed MERS had never made an appearance, there are plenty of sheep, goats, and cows.

Camels, though—that was trickier. No camels, as a general matter, wandering about in the Low Countries. Where might the scientists find accessible camels that were also a long way from the apparent traveling path of MERS-CoV? "And we thought of the Canary Islands camels," Haagmans told me. "We had a contact there."

Spain's Canary Islands? They have camels? As it turns out, they do. The Canary Islands lie off the northwest coast of Africa. Colonists first imported dromedary camels to the islands in the 15th century, and a small herd has remained ever since, replenished a while ago with three adults imported from Morocco. The Spanish dromedaries—the same type of camel that populates North Africa and the Middle East—are used for the benefit of the islands' tourists, and like much of the world's livestock, these dromedaries undergo regular veterinary inspection.

Serum samples from these Canary Island camels, taken during such an inspection in 2012, were already in storage. An international team ran the sera through the full array of virus-tracking tests.

"And to our surprise," Haagmans says, "we saw positive."

Of the 105 camel samples they tested, that is, 9 were positive for antibodies indicating that MERS-CoV, or something that looked just like it, had at some point lived and replicated inside those particular camels. The Canary Islands! As far as anyone knew, no Canary Islands person had ever become ill with MERS. All the European noncamel livestock was coming up negative for the virus, by the way—sheep, goats, etc., showing nothing. Only the Spanish camels.

The Dutch researchers had contacts in Oman as well, so with Omani colleagues' help, they now added camel samples from that nation to their study—50 blood samples, extracted during routine screening from the jugulars of retired Omani racing camels.

Every one of the Omani samples showed traces of antibodies to MERS-CoV. "To our knowledge," the study's authors wrote carefully in their October 2013 account in The Lancet Infectious Diseases,"the camel populations in Oman and the Canary Islands are not connected." To put that in less dignified language, something weird was up with MERS and dromedary camels, including camels that had plainly never gotten anywhere near the poor index patient from Bishah.

And the possibilities that suggested, given that the world currently contains more than 25 million camels, nearly all of them domesticated and thus in regular close contact with people, were grave indeed.

The questions surely forming in your mind right about now—How? Why now? What might this mean? What about the bats?—were the same ones the scientists were wrestling with. They still are. "Tip of the iceberg" is perhaps not the first metaphor to come to mind for a saga that features camels, but it's the one Jon Epstein used the first time we talked. In the Kingdom of Saudi Arabia, where a new Ministry of Health-run coronavirus website now updates grim statistics every day, the MERS epidemic—in other countries it's still an unusual viral disease, but in the kingdom it qualifies as an epidemic—steadily continues to spread.

May 5, 2014: 117 cases passed away May Allah have mercy upon them. May 7, 2014: 121 cases passed away May Allah have mercy upon them. By Friday May 16, the Saudis' posted "cases passed away" total stood at 160, with 514 cases diagnosed inside the country; internationally, according to the World Health Organization’s tracking, the diagnoses through the end of this past week totalled 572, with 173 deaths. The many global points of confirmed MERS diagnoses now include Athens, Greece (male health care worker, just back from Saudi Arabia); Batu Pahat, Malaysia (male religious pilgrim, just back from Saudi Arabia); and the two American cities—Munster, Indiana, and Orlando, Florida— in which health care workers returning from Saudi Arabia have in recent weeks received MERS diagnoses.

Saudi Arabia remains the epicenter, as it was during the detective hunt set off by the man from Bishah. This spring had already proved a season of exceedingly bad news there, from the public health perspective. Then last month, confirmation came from a new international study, led by researchers from King Saud and Columbia Universities: MERS-CoV, either the active virus or its biological footprint, was in three-quarters of the kingdom's camels too.

View Images Jonathan Epstein, a veterinary epidemiologist, holds an Egyptian tomb bat captured in Saudi Arabia. A piece of genetic material matching MERS-CoV was detected in one of these bats found in the town of Bishah. There is currently no evidence that any of the human cases have had direct exposure to bats. More work needs to be done to understand whether MERS-CoV may be transmitted from bats to camels or people. K.J. OLIVAL, ECOHEALTH ALLIANCE 2014

Ground Zero

Envision a certain desert clearing in Saudi Arabia, where a man I know, Ameer Mohammed, was walking two weeks ago in the softening heat of early evening. This place, where scrubby plants poke between the rocks and the light at that time of day is deep and bronzy, is about two hours' drive inland from Jeddah, Saudi Arabia's west coast port metropolis. Ameer is 32, married, a college-educated, urban man. He runs an events-management company, arranging conferences and so on. But every weekend, because he loves the natural world that stretches beyond the intensely built-up Jeddah, he leads casual hiking and camping excursions—I spent all of December in Saudi Arabia, and joined Ameer and his friends for one of these excursions—into the desert, where there are camels.

This is why Ameer was walking. The day's group fun was over. His friends were back at the clearing, resting near their parked SUVs, and Ameer had now taken along with him one companion only, a young Saudi recently home from years of study in the United States. Ameer has been following the most recent news reports anxiously and closely, as has every literate citizen of Saudi Arabia, but this latest suggestion, that MERS-CoV might somehow be tainting the kingdom's camels, had caused him to recoil. He was not willing to believe it. He was about to do a defiant thing.

A crazy defiant thing, I yelled at Ameer, over the phone, when he told me about it afterward. Had he asked his wife's permission first?

"No," he said.

Let me backtrack. Remember the bats? All those bat bits, the material Epstein and his veterinary companions collected in the fall of 2012, were chemically teased apart and microscopically examined inside Lipkin's laboratories at Columbia, in the process of which they found a fragment of genetic coding, from a single bat, that showed the right markers for MERS-CoV. One fragment. But there it was, and it matched the virus that killed the man from Bishah. This made Epstein pretty certain that MERS-CoV has a "bat origin," as he puts it. And although every researcher I talked to agreed that this is likely the case, the most pressing anxieties this spring, among Saudis as well as international scientists, can be summarized in three words: contagion, hajj, camels.

Contagion: No question about it now; MERS passes human to human. Not as readily as SARS did, mercifully, and for a long time the Saudi news reports about "coronavirus," as the Saudis preferred to call it, were sporadic and only mildly worrisome.

View Images In the port of Djibouti, a herd of camels is loaded onto a ship bound for Saudi Arabia. Middle Eastern countries import tens of thousands of camels from eastern Africa annually. Scientists don't yet know where the MERS virus originated or how camels got it, but it has been found in African countries and as far away as Spain’s Canary Islands, where a tiny population of camels lives. MATTHIEU PALEY, CORBIS

While I was there in December, for a project unrelated to MERS, the total death toll was around 70. It was mounting, but there are 28 million people in Saudi Arabia, and everybody knows the greatest daily health challenge any Saudi faces is surviving an ordinary outing in a car. The drivers are all men, of course, and between the vrooming young hotshots and the hired foreign drivers wildly improvising road protocols, the number of national traffic fatalities—more than 18 deaths a day—is the mortality statistic Saudis know best. "I mean, give me a break," one Saudi friend said last week, when I mentioned that in all our extended conversations during my visit, MERS had never come up. "I'm more likely to die in a car. It's really thrown out of proportion."

For reasons no one understands, though, something happened this past spring, when the number of reported Saudi cases doubled, with the sharpest jumps in and around Jeddah. At the beginning of April the Saudis' MERS diagnosis count was 166. Two weeks later it was nearing 200, and new case totals began appearing daily in the news. Many of the patients who died had had previous health complications, but not all of them. (The man from Bishah, for example, had no reported preexisting heart or immunity trouble.) And to fuel the general unease, MERS was clearly being transmitted most readily inside medical settings, among hospital patients and health care workers.

Masks now began appearing on people's faces in the street, hand sanitizer began disappearing from supermarket shelves, and Saudis began reacting one of two ways to a cough or a sneeze or a fever: either hurry to the hospital, because you need to get tested for MERS, or go anywhere but a medical setting, because that's really where you contract MERS.

"If you had a dental appointment, you're not going," a teacher friend told me. A friend who works for an international company told me, "My daughter had a fever, but I went to the private pediatrician, not a hospital." Ordinary colds and flus are circulating around Jeddah right now—two friends I called were coughing into the phone as we talked last week—and also there are seasonal dust storms, which are hell on the respiratory system, so nervous humor among colleagues is rife.

"Every time someone sneezes, I make a corona joke," a graphic artist said. "My friends are sending me jokes all the time." She meant via social media, which is enormously popular in Saudi Arabia. Twitter and WhatsApp broadcast worried posts from parents wondering whether schoolchildren should be kept home, and although Saudis I talked to were still sending their own kids off, some schools have already advanced their end-of-year exams to the last weeks of May to hasten the conclusion of the school year.

From Jeddah, where the recent case surges have been so intense, I heard a few stories about eerily deserted playgrounds and some sober interest in whether the niqab, the black face veil worn by many Saudi women, protects against MERS. Consensus: It does not. A Jeddah filmmaker told me that in her mosque a few weeks ago, the imam worked MERS into his sermon, reminding worshippers that although your destiny in this life is decided by God, you cannot know what God has in mind for you, so take precautions, wash your hands, mask yourself in crowds—and join me, this imam said, in feeling shame for that small group of physicians reported to have stopped showing up for work because they're afraid of the virus.

The Saudi minister of health, Abdullah al-Rabeeah, spoke to the nation publicly on April 20, reassuring Saudis in a televised news conference that there was no need for stricter preventative measures against MERS. He was removed from his post the next day. (Ali Zaki, the diagnostician who guessed correctly about the coronavirus first, was fired too—sacked in late 2012 by the Saudi Ministry of Health, Zaki says, not long after he sent the international infectious disease newsletter "ProMED" a note about the interesting case from Jeddah. That's why he's gone home to Egypt.) By last week the new acting minister of health, Labor Minister Adel bin Mohammed Fekeih, was using language that translates to English headlines as "all out efforts," and anybody who clicks on that Ministry of Health website now seespictorials and animated video indicating the things not to do: Avoid touching your eyes, nose, and mouth. Don't sneeze without a tissue. Don't forget to discard your tissue properly into a wastebasket. Don't get too close to people already infected, and if you must, use a mask.

View Images Pilgrims pray at Mecca's Grand Mosque last October during the hajj, when more than a million Muslims gather there from around the world. Last year's hajj saw a sharp decline in attendance, apparently because of MERS fears. As cases continue to mount, including two recent cases in the U.S., world health officials are concerned that this year's hajj could spread the virus worldwide. FAYEZ NURELDINE, AFP/GETTY

LOOMING CONTAGION NIGHTMARE

The largest scheduled human migration in the world, though, is due to bring many hundreds of thousands of people into and out of Saudi Arabia this coming October. This is the hajj, the international pilgrimage to Mecca, a trip every Muslim is supposed to make once, if physically possible, during his or her lifetime. Jeddah is the closest big city to Mecca, and its airport is the standard transfer point for religious pilgrims; they come and go daily all year, as Muslims also frequently travel to and from Saudi Arabia for less formal spiritual visits to Mecca.

But the very nature of the formal hajj is an annual nightmare in its possibilities for public health problems. Side by side, for five days straight, often spending the nights in close-packed family tents, Muslims pray together and mass around the Kaaba, the great black cube that is the physical center of Islamic worship.

Saudis are known to have an extremely good track record of keeping people healthy during the hajj. Even so, in the wake of this year’s spring MERS diagnoses surge, the prospect of a million foreign visitors converging on Mecca and then returning home is alarming health officials both inside and outside Saudi Arabia. Last year, more than1.4 million foreign pilgrims arrived for the hajj; that figure was down by more than 400,000 from the previous year, a drop widely attributed to MERS concerns. Even a much lower 2014 total will still be a daunting number of people to crowd into one place. Last week the Egyptian Ministry of Health was reported to be considering a hajj travel ban for Egyptians this fall—"depending on the epidemiological situation in Egypt and Saudi Arabia," an Egyptian health official said.

The general nature of viruses, too, makes for a race-against-time complication, fiercely intensified by the prospect of the hajj. Since the epidemic began, researchers examining samples have been relieved to note, the MERS virus itself appears not to have changed its form. But as Spillover author David Quammen said this week, "The more humans it gets into, the more opportunities it has to evolve—into a virus that's really good at replicating in humans. That raises the possibility that it could mutate into a form that's not only very virulent, but also very transmissible. That's what we don't want."

And finally, as though an international contagion mystery with accelerating stakes were not burden enough, there is this matter of the camels. In the United States and Europe there is really no single equivalent to the Saudi Arabian camel. Camels in the kingdom are like dairy cows, beef cows, racehorses, pulling horses, beloved Labradors, and living daily reminders of holy scripture, all in one. (Camels appear, honorably, in the Quran.) The main cities of Saudi Arabia are dense constructions of steel and concrete, lined with international fast-food outlets, spiky with half-built skyscrapers, crisscrossed by those lethal highways. Nobody ventures into urban streets with camels, as one might see in certain cities of India.

But just a few miles out along the freeway, as soon as the desert space begins to stretch between buildings, herds of camels are as familiar a sight as countryside cows in my home state of California. Saudi butchers sell camel meat. Camel dishes are a specialty of some restaurants. Camel milk is regarded as wholesome and good for the human gut. So the scientific study that made international news last month, finding signs of current or past MERS-CoV infection in most of the kingdom's camels, was a rattling assault upon multiple sectors of Saudi society—food shoppers, farmers, restaurant cooks, butchers, racing-camel trainers and stable hands, market camel handlers, and families—like the index patient's—with prized camels living placidly in the side yard.

Those particular pet camels, incidentally, proved not to be infected. But after the startling Canary Islands and Omani camel findings, Saudi researchers, working with a Center for Infection and Immunity team led by virologist Thomas Briese, were able to accumulate an enormous amount of camel serum—some of it fresh, and some, pulled from storage, dating back as far as 1992. Even that serum, the stuff more than two decades old, contained MERS-CoV antibodies.

The conclusion? This virus, or something nearly identical, has been infecting Saudi Arabia's dromedaries for at least 20 years.

And fully a quarter of the living camels the researchers studied—the kingdom's current dromedary stock—appeared to be carrying live virus. It wasn't that the camels were acting like human beings with MERS; camels get sick sometimes, displaying random symptoms such as sneezing and runny noses. But nobody's identified an outbreak of critically ill Saudi dromedaries, which is both perplexing and worrisome. Assuming camels are somehow passing the virus to humans—and that MERS-CoV is not also coming from some other animal reservoir, which the study’s lead author, Saudi mammalogist Abdulaziz Alagaili, has suggested as one possibility—then there's no easy way to tell exactly which camels may be dangerous up close.

Wait, it gets worse. Many Saudi camels are imported. They come from neighboring Middle Eastern countries, in part, but also from countries in eastern Africa, including such already beleaguered places as Sudan and Somalia. Just now online, not scheduled for formal publishing until this summer, is a brand-new Centers for Disease Control and Prevention report finding widespread evidence of MERS-CoV in African dromedary camels too.

View Images A Muslim pilgrim wears a mask as she walks to Mecca's Grand Mosque. From summer 2012 to May 13, 2014, the Saudi Arabian health ministry has reported 495 cases of MERS in the kingdom, with a total of 152 fatalities. Officials warn that one way the virus is likely transmitted between people is coughing and sneezing. FAYEZ NURELDINE, AFP/GETTY

Nobody Really Knows

The unknowns implicit in these new findings are unnerving. Are African villagers and camel handlers—in communities without specialized testing or even decent hospital access—walking around now with a contagious deadly virus they don't know they have? It's possible. Are Africans carrying it but not dying from it because they've somehow adapted, in a way urban Saudis have not? It's possible. Are Africans dying from it but going undiagnosed, just because MERS has not become a national preoccupation in places like Sudan, which have other dreadful health problems to attend to? It's possible.

What about Australia, separated by a mighty stretch of ocean from the hospital infections of Jeddah? Australia has camels. They're not domestic; the Brits brought them in the 19th century as pack animals, and the camels were let loose to go feral. They now number about 300,000. A zoonotic disease scientist in Australia told me MERS research is now under way there as well: "diagnostic and surveillance activities, which currently includes MERS in bats and camels," he wrote in an email, adding that he could not yet provide further details.

The World Health Organization has assembled a special emergency MERS committee, with members from 17 countries; they held their fifth conference today. The Food and Agriculture Organization of the United Nations has called an extraordinary multicountry MERS meeting for later this month, in Oman.

Among international organizations that monitor health and livestock, the MERS research is prompting both new vigilance and deep uncertainty. The World Health Organization has assembled an emergency MERS committee, with members from 13 countries. The Food and Agriculture Organization of the United Nations has called an extraordinarymulticountry MERS meeting for later this month, in Oman. But after all these diagnoses and all these studies, nobody yet knows for sure how the virus is passing from animals to humans, or even if that kind of interspecies transfer is still under way. To date there's no evidence of unusually high MERS rates among people who butcher or work directly with camels, either; a few patients had been in contact with camels, but many more, as far as is currently known, had not.

Nobody knows whether the virus can pass to people in camel meat or milk, either; there's a kingdomwide screening effort under way now. A couple of weeks ago WHO and Saudi health authorities began including camels into their lists of things to avoid: Don't eat raw camel products, mask up if you have to work with camels, stay away from them if you don't.

And those warnings, finally, were what pushed my friend Ameer Mohammed to set out on his defiant Saturday walk. "It didn't make any sense," he told me. "There are so many rumors. We've heard so many things. I just wanted to say hi to Abu Talib."

Abu Talib keeps camels. Out by that clearing, where Ameer likes to camp, if you scramble up the craggy rises of rock at the edge you can see camels down where Abu Talib likes to pasture them, at the other side of the rocks, where the desert goes flat and looks as though it stretches to the farthest curve of the Earth. The only sounds you hear atop those rocks are wind and the grunting of camels, and Ameer told me that when he and his friend reached Abu Talib, the camelkeeper invited them to sit with him beside the camels' fence.

"I said, 'So what's the deal with this corona thing?'" Ameer told me.

"And he said, 'Nothing. It's all rumors. I got a veterinarian to come here and check the camels out.' He told me there was no trace. He said, 'I'm a believer that camel milk is a cure for many diseases.' I said, 'What if it was something—a bat or something bit the camel, or this bat, I don't know, pooped somewhere, and the camel got infected?' And he was like, 'Out here? In the desert?' No bats.'"

The three of them sat quietly for a moment, Ameer told me. It felt peaceful. The camels were still. "Then I said, 'OK. You know what? Let's have some camel milk.'"

Abu Tabib called to his helper, who washed a big stainless steel bowl with soap and water, and walked over to a mother camel beside her baby. The helper milked the camel, standing all the while, the milk squirting straight into the bowl. When the big bowl was full, he brought it over and ladled it into three small bowls. Ameer and Ameer's friend and Abu Talib all nodded to each other, and they drank.

"Very heavy, very sweet, very therapeutic," Ameer said, after I stopped shouting at him over the phone. If I were still in Saudi Arabia at this moment, I told him, I would be smacking him upside the head.

"I know," he said. He was laughing. "I'm feeling great. Never been better. I promise you. Nothing is going to happen."