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How a bat virus became a human killer

August 22, 2014, 11:00 AM UTC
Handout transmission electron micrograph shows particles of the Middle East respiratory syndrome (MERS) coronavirus
Photos: Reuters / Photoillustration by Jaclyn LoRaso

This article is part of our Contagion package, a series that explores the science of how things spread.

By all appearances, the camel had a cold. One of nine camels kept in a barn outside Jeddah, Saudi Arabia, the animal was sick and expelling nasal discharge. The camel’s owner did what he could to help, swabbing his own finger in vapor rub and applying it inside the dromedary’s nose.

Seven days later, the owner—age 43 or 44, depending on the source—began feeling tired and developed a runny nose and cough. Five days after that, he found it harder to catch his breath. Three days later he was admitted into the ICU with severe shortness of breath. Fifteen days later, the man was dead. That was last November.

The camel recovered.

As it turns out, what the runny-nosed animal had wasn’t a cold at all. It was MERS, or Middle Eastern respiratory syndrome, the same virus that would kill its owner—likely, MERS’ 72nd reported victim—some four and a half weeks later.

Relatively common and benign in camels, MERS—which belongs to the family of coronaviruses that includes both SARS and the common cold—first emerged as a threat to humans in September 2012. Spiky in shape and only a few nanometers big, the virus has been making its slow, but often-deadly spread around the globe ever since: according to latest lab-confirmed stats from the World Health Organization, MERS-CoV has now infected at least 837 people and killed 291 of them.

Most of these cases have occurred on the Arabian Peninsula (Saudi Arabia has reported more than the WHO with 723 infections and 299 deaths), though patients have also turned up far from Jeddah—in more than 20 countries, including locales as far away from the Middle East as France, Malaysia, and even Munster, Indiana. (In late April, a U.S. resident, who had been working at a Saudi medical facility, walked into the E.R. at Munster’s Community Hospital—and, in a remarkable example of good hospital procedure and care, was successfully treated and later released.)

This spring, infections rose at an especially alarming rate. In April, the global number of new MERS cases reported surpassed the total reported in the previous two years, according to the European Centre for Disease Prevention and Control, Europe’s counterpart to the U.S. Centers for Disease Control and Prevention. And in early June—shortly after Saudi Arabia’s health minister was sacked—that country’s Ministry of Health announced the count was even higher than thought, revealing that the previous minster had missed 113 cases (92 of them now deceased).

Ebola may have the world terrified these days, but earlier this year, as cases spiked and jumped continents, MERS-CoV was the virus that had the globe’s public health officials on edge. Its spread has slowed down this summer, but the pathogen hasn’t gone away—nor, worryingly, have epidemiologists completely figured it out.

The strange power and unpredictable nature of contagion, whether it be the spread of disease or a whimsical social fad, has long fascinated scientific and creative minds alike. And at Fortune, we’ve been intrigued by it too. In this series of essays, my colleagues and I have set out to trace a wide range of “outbreaks”—from that of the MERS-CoV to less deadly spreads like M&A rumors, market panics, book sales, and that modern phenomenon known as the “selfie“—with the hopes of better understanding them. Some contagions are more easily explained by science than others, and one would expect MERS, like Ebola, to fall into the category of the scientifically explicable.

Yet what makes MERS so scary to some, is just how much about it remains in the realm of mystery—starting with something critical: how exactly humans become infected and how they pass the virus on to others. There are clues with MERS—the sick camels, for one—but currently, bats, camels, hospitals, unprotected health care workers, unclean surfaces and politics have all shouldered a bit of the speculative blame. One Australian epidemiologist, citing “paradoxes” involved in MERS’ spread, recently even suggested that bioterrorism may have a role.

Meanwhile, two years since MERS was first discovered in humans—and now in the shadow of Ebola—the tally of patients and fatalities continues to climb. Saudi Arabia reported two new cases just last week.

The WHO has convened six Emergency Committee meetings on MERS, which by the health organization’s latest reckoning kills 35% of its victims. But while MERS has earned the carefully trained eye of the world’s medical community, it has not yet been deemed a “public health emergency of international concern.”

Even so, it has made for an unsettling state of affairs given the number of pilgrims traveling to Saudi Arabia this summer and fall. Ramadan, the peak season to perform the Umrah (a religious journey to Mecca that many Muslims make), drew more than 6 million to the country in July. And in October, many more people from all over the world will crowd into Islam’s holy city for the Hajj—a pilgrimage to Mecca that Islamic tradition requires Muslims (who are physically and financially able) to undertake at least once during their lifetimes. Some global health officials fear that, as 2.5 million additional people converge on a single city during a five-day period in October, the stage may be set to turn MERS—which is potentially one mutation away from becoming a more virulent, transmissible disease—into the world’s next pandemic.

Accordingly, scientists are scrambling to understand how a virus that had been circulating in camels for decades suddenly took root in humans and started spreading around the world.

In many ways, MERS is a familiar story, just the latest in a number of newly-discovered pathogens to have landed on the radar of public health officials in recent years. As with nearly two-thirds of emerging diseases—including HIV, SARS, H5N1 (bird flu), and H1N1 (swine flu)—MERS started making trouble for humans after a zoonotic event, or that random moment when it jumped from an animal to humans.

These events are increasingly common, both because they’re being detected more often, and because there’s more and more opportunity for such events to occur, says David Quammen, who has written a book, Spillover: Animal Infections and the Next Human Pandemic on the subject. Interactions between humans and animals have happened forever, but modern development—such as the building of roads and timber camps in tropical forest, or factory farming—has increased the scale and frequency of them. Plus disease can travel much further and faster these days.

Take SARS, or Severe Acute Respiratory Syndrome, the coronavirus that gave the world a scare in 2003 when it infected 8100 people and killed 774 of them in a matter of months.

First identified in China’s Guangdong Province in November 2002, SARS is thought to have originated in bats and been passed to humans by way of the civet, a cat-like animal that was sold in wildlife markets and eaten as a delicacy in parts of China. Once in humans, the virus spread through the air with terrifying speed and reach—most notably when it infected 321 residents of Amoy Gardens, a Hong Kong apartment complex (a 2006 paper on the outbreak found that the virus entered apartments via bathroom floor drains.) The virus ultimately traveled to more than 30 countries, helped along by a handful of “super-spreaders” or individuals who transmit disease particularly effectively. While staying in Hong Kong’s Metropole Hotel, for example, a doctor from Guangdong infected 13 people including those who carried SARS to Canada, Singapore and Vietnam.

SARS was far more transmissible among humans than MERS currently is, but it was also less lethal, killing roughly 10% of its victims compared to the 35% of patients who have died from MERS. This makes MERS a less imminent threat, but also a potentially terrifying one should it mutate into a more transmissible form, an opportunity the virus gets every time it spreads between humans, or from animals to humans.

Watch: Video of virus-sized particle trying to enter cell

But unlike SARS, which is believed to have jumped from humans to animals just a few times, MERS (now that we know it exists) appears to be jumping repeatedly—the spread of the virus propelled along by a number of scattered separate zoonotic events, a pattern that’s mysterious for a number of reasons.

While that puzzle is still being pieced together, it’s likely that this story begins, as SARS did, in a bat. Reservoirs for many a nasty virus (from Ebola to rabies to SARS), bats have a long history of spreading disease—typically through saliva or their tiny droppings—to others in the animal kingdom, from house pets to livestock to humans. In July, scientists published findings that a virus found in the feces of a Cape serotine, a South African bat, was of the same species—and offered the closest genetic match yet—to the MERS-CoV.

Scientists suspect it was a bat that brought MERS to dromedary camels; the animals have tested positive for MERS antibodies dating back to at least 1992 (antibodies are a sign of previous infection). More recently, antibodies have been found in 75% of camels in Saudi Arabia—the virus was active in 35% of them—as well as in camels many countries away in Egypt, Oman, and the Canary Islands off the coast of Spain.

While epidemiologists aren’t certain that the virus’ first leap to humans came via camels, the animal is a likely source. The camel has been proven to be the culprit in at least one instance—that of our 40-something-year-old camel owner near Jeddah. (In late June, a team of Saudi researchers reported in the New England Journal of Medicine that full genome sequences in the virus found in both the human victim and the infected camel were identical.) And the first known patient to die of MERS, a businessman living in Bishah, Saudi Arabia, also had exposure to them: he kept four camels as pets.

The linkage makes sense: On the Arabian Peninsula, where camels are ubiquitous and considered honorable beasts, there is certainly opportunity for zoonotic events.

Slobbering animals even when healthy, camels shed virus through their noses and stool; recent epidemiological research from Qatar also found the milk from many infected camels contained MERS. (It’s unclear whether the milk was infected directly by the camel or contaminated through a calf’s suckling.)

Close contact with the animals, moreover, is hardly rare. A source of livelihood and entertainment, camels in the Middle East are raced like horses and trotted out in beauty pageants (as contestants). They’re regularly consumed for milk and meat, sometimes in the raw forms that have been flagged as possible transmission routes. Kept as pets and livestock, owners are intimately involved in the feeding, care and birthing of the creatures, contact that the WHO and a number of governments now advise be done with facial masks and gloves. (Offended by such guidance and the suggestion the animal has anything to do with transmitting a lethal disease, some Saudis, particularly loyal to the animal, have posted videos of themselves on YouTube kissing camels.)

But if camels are the zoonotic link, then it raises another, perhaps bigger mystery: why didn’t MERS jump sooner? Here, the best answer, epidemiologists say, is that it almost certainly did—we just didn’t notice.

At least one MERS outbreak—which infected 13 people in a Jordan hospital in May 2012 and was discovered in hindsight—predates the discovery of MERS (at the time, doctors in Jordan believed the illness to be pneumonia). Recent surveillance efforts in Saudi Arabia and Qatar have also turned up a number of individuals who either have MERS antibodies (meaning they once had the virus) or are asymptomatic—meaning they have the virus but show no sign of it—suggesting there are far more cases than officially tallied.

As scary as MERS is—and Ebola, too, for that matter—most infectious disease experts say the outbreaks are cause for cautious vigilance, not panic. What keeps them up at night, rather, is the next one.


For more inside the world of contagion, see

CONTAGION—How things spread. Introducing a new Fortune series

• Part 1: How a bat virus became a human killer

• Part 2: How the MERS virus made it to Munster, Indiana

• Part 3: How M&A rumors spread

• Part 4: How market selloffs happen

• Part 5: How Americans fell in love with a 685-page economics treatise

• Part 6: How the “selfie” became a social epidemic

• Part 7: How studying Twitter became an academic craze