A tiny young woman crouches just outside the airport, crying softly into her thin shawl. It's cold out, but her sleeping toddler is heavy and warm in her arms.

Travelers swarm around: Himalayan trekkers load up expedition backpacks. A Chinese tour group boards a bus. A dozen flight attendants in crisp blue suits and heels click by.

Saro Kumari Mandal, 26, covers her head completely, a bundle of grief.

Hundreds of young Nepali men excitedly wave final goodbyes to friends and family. On this day 1,500 will fly out of the Kathmandu airport bound for jobs mostly in Malaysia, Qatar or Saudi Arabia — jobs that are urgently needed by the people of this desperately poor country.

But on this day, too, six young men will come back in wooden caskets, rolled like suitcases out of baggage claim on luggage carts.

On the wooden lid of one someone has written in black marker: "Human Remains, Balkisun Mandal Khatwe, Male — 26 years — Nepali."

Saro's husband — another victim of a hidden and escalating tragedy.

The number of Nepali workers going abroad has more than doubled since the country began promoting foreign labor in recent years: from about 220,000 in 2008 to about 500,000 in 2015. Yet the number of deaths among those workers has risen much faster in the same period. One out of every 2,500 workers died in 2008; last year one out of every 500 died, according to an Associated Press analysis of data released by Nepal's Ministry of Labour and Employment.

In total, over 5,000 workers from this small country have died working abroad since 2008— more than the number of U.S. troops killed in the Iraq War.

The causes, in many cases, have been mysterious. Natural death, heart attack or cardiac arrest are listed for nearly half the deaths. Most families are notified that their loved ones simply went to bed and never woke up. That's exactly what Saro was told.

But now medical researchers say these deaths fit a familiar pattern: Every decade or so, dozens, or even hundreds, of seemingly healthy Asian men working abroad in poor conditions start dying in their sleep. It happened in the U.S. in the late 1970s, in Singapore about a decade later and more recently in China. The suspected killer even has a name: Sudden Unexplained Nocturnal Death Syndrome.

Next year, an international consortium is launching to investigate and hopefully offer solutions.

For today's arrivals, they're too late.

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Nepal exports iron and steel, carpets, some vegetables — but mainly, Nepal exports men. It even advertises them.

"Nepalese workers are well known for their hard work, dedication and loyalty," boasts the Nepalese Embassy website in Doha, Qatar, where a pre-World Cup construction boom employs about 1.5 million migrants. The Nepali workers "are comparatively cost effective," says the embassy, and they're experienced at "working in the extreme climatic conditions."

The unskilled workers fill a host of global demands: building highways, stadiums and houses in Gulf states and guarding shopping malls, sewing sweatshirts and assembling televisions in Malaysia. Anyone who has bought imported sportswear or electronics, or who plans to go to the 2022 World Cup in Qatar, may be using the products of their labor.

Nepali law bans recruiters and employers from charging fees. Qatar, where Balkisun was working, prohibits the fees too. But in reality everyone has to pay for these jobs. The men borrow at 36 percent interest rates from money lenders or sell off family land to get the $1,100 stake needed for recruiters, airline tickets and more. Conditions vary by country and employer, but it's not uncommon for workers to find themselves living a dozen or more to a room, sleeping stacked on three-tiered bunks, working 10- to 15-hour days, seven days a week, for years.

If they're lucky — and some are — they can send home wads of cash, about $300 a month. Often, however, they are tricked or cheated out of their earnings.

About 10 percent of Nepal's 28 million residents are working abroad. They send back more than $6 billion a year, amounting to about 30 percent of the country's annual revenues. Only Tajikistan and Kyrgyzstan are more dependent on foreign earnings.

Some come back maimed or disabled, like Salit Mandal, who rolled off a third-level bunk in Malaysia and smashed in his skull. He's in debt, partially paralyzed, and lives with his parents.

"I have no idea what I'm going to do, how I'm going to raise them, because I can't move," he says, gazing at his three children. "If my hands and legs could move I would do something, but I can't do anything at all."

His family had pinned their hopes on him after he returned from an earlier stint in Qatar with enough money to build a five-bedroom house. Now his mom takes a visitor aside and says the situation is horrible — Salit can't squat by himself over the pit toilet, she says, and she has to clean him up afterward.

His little brother Jamun Mandal, 24, is next in line. He's abandoned his aspirations of going to college and has paid the recruiting broker. He holds up a passport.

"I know it sounds weird to be planning to go, because people die, disappear, they come back in comas," he says, "But what to do?"

Sitting behind her tidy desk at the Department of Foreign Employment, spokeswoman Rama Bhattarai shrugs off the death toll.

"I'm not trying to be insensitive but we have sent millions of workers to more than 100 countries, and so yes, sometimes people will die. They die as foreign employees, they die here when a bus goes off a cliff," she says.

Others are more incensed.

Krishna Dawadee, acting director of Kathmandu's one-stop work permit center, waves an arm at the hundreds of young men gathered at the service window seeking final work approvals. Outside the gates, life insurance salesmen grab at the prospective workers' arms and sweaters, trying to pull them into their offices to sell policies.

"These are our youth, draining out from our country," Dawadee says. "I am very much worried about these people."

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Six weeks after Balkisun Mandal Khatwe made the long journey from his village to the employment office, his wife travels back across the country to retrieve his body.

His casket arrives on a 7 p.m. flight. It takes more than three hours to get paperwork sorted out between his barely literate family and the airport bureaucrats who needed a death certificate, identifications, work permits and more.

Finding transport is less complicated: The casket slides easily into a custom-welded coffin rack. The government of Nepal arranged to have 10 trucks so equipped after labor exports — and deaths abroad — began to rise.

The badly rutted and cracked road from the Kathmandu airport to Belhi village is closed after dark because too many buses have plunged off the narrow, steep, sharp curves. But under starry skies, the truck was waved past checkpoints by police who spotted the rooftop coffin while warming their hands over small fires. After death, Hindu funerals must take place as soon as possible, hopefully by the next dawn.

Saro and her son, just 3 years old, jolt around the backseat for a precarious eight-hour journey. They jounce in their seats as the truck bottoms out in potholes, jerk side to side as it races around corners.

When the truck reaches Belhi, hundreds of women in traditional saris, men in their work clothes and children pour into the narrow dirt street, tears streaming down their faces. Everyone pushes and shoves to get close to the coffin. Some stand on rooftops. Others crowd a balcony.

Nepal is one of the poorest and least developed countries in the world, and Belhi is one of its poorest places. The Mandals live eight people to a room in one of about 700 mud-and-stick homes set among dry, sparse rice paddies. A shared cellphone is passed from house to house. People are chronically hungry, living on less than $1 a day.

The Mandals and their neighbors are marginalized in every way: Ethnically, they're from the "untouchable" caste, and they speak Maithili, a language more common in India, just a few miles south.

Family members wrestle Balkisun's coffin off the truck. Mohammed Tohit, 28, watches from across the street, then looks at his hands, the cloudless sky, a distant mango tree. He wipes a wet cheek.

"I knew this guy, and the thing is when you see people coming back in a coffin like this, it's hard," he says.

He adds quietly: "I'm leaving for Saudi in 10 days."

Tohit is the envy and inspiration of the village. He worked in Malaysia for almost six years sewing clothes for Nike, Lacoste and Columbia Sportswear, saving more than $20,000. That was enough to build a sturdy, cement two-bedroom house with plaster walls and a brick foundation. He bought a piece of farmland and a television set. There's a cow staked outside his woven fence, among the goats and chickens. His round-cheeked, 6-month-old daughter, Saieha, is shy in the arms of his wife, Jarina Khatun.

"I am scared, sure, but I have no way to earn anything here," he says. "I have no choice but to leave again."

Balkisun's brother Ramasis, 35, went for work in Dubai but returned three months later with a debilitating mental illness. Bidhya Nanda, 25, the youngest, is still in the Gulf, working as a janitor in Saudi Arabia. Another brother, 30-year-old Ramkisun, flew back from Malaysia, where he was working in factories making Sony and Panasonic products, when he learned of Balkisun's death.

Their father, Kalaru, hates to see his sons go, but has no option. "We are poor and we don't have any way at all to earn money in our village."

The news of his son's death came in a morning phone call two weeks earlier. It seemed impossible.

Here's what people say about Balkisun: He was a good lad. He didn't smoke. He got along with everyone. He was very helpful. He was honest.

Balkisun was working for Habtoor Leighton Group in Qatar, loading trucks to build new highways. The highway was being built as part of broader infrastructure improvements for the 2022 World Cup, said his supervisor Ganesh Khang Mandal, 48.

Dubai-based HLG did not respond to requests for an interview. Australia-based CIMIC, a 45 percent owner of HLG, said in a statement that it did not want to comment.

Saro had chatted with Balkisun through Facebook Messenger just the evening before his death.

Although he confided to friends he was having a difficult time with his job, money and housing, he told Saro that everything was going well. He took a selfie in his yellow work hardhat, eyes grinning through protective sunglasses, his face covered in a blue scarf to fend off the harsh climate. He told her about a big festival that day.

"OK, I'll call you tomorrow morning" — the last words her husband said to her.

This is what happened, according to his supervisor: "After work he went to dinner at 7 and bed at 10. In the morning we tried to wake him up but he didn't respond. We took the body to the hospital where they did an autopsy and said it was cardiac arrest."

He'd been in Qatar less than a month.

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Authorities in Nepal say their citizens seem to die abroad more frequently than their equally vulnerable Sri Lankan, Bangladeshi and Indonesian co-workers, but the explanation for the increased mortality has been unclear.

"It's usually sleeping disease," said Kumud Khanal, vice president of the Nepal Association of Foreign Employment Agencies, which represents more than 400 registered agents. "We get the report that he was talking with friends in the evening, had dinner and went to bed, and in the morning he was found dead." The deaths are reported as a hypertension problem, he said, like heart attack or cardiac arrest.

But medical experts say there have been waves of deaths before among young, rural southeast Asian men working abroad in physically stressful conditions.

"I see some familiar patterns here with Nepalese workers," said Patrick Clarkin at the University of Massachusetts, Boston, who has written about the biology and epidemiology of Sudden Unexplained Nocturnal Death Syndrome. "I suspect that there would be little harm in improving the diets and living conditions of these young men. Something as simple as a multivitamin could go a long way and with little risk."

In rural Nepal, people eat rice, lentils and seasonal greens around 10 in the morning, and a second meal of rice and vegetables in the evening. Milk and eggs are almost always available as well.

Abroad, Nepali workers also eat twice a day, but the mainstay is whole meal flour flatbread with some pickle or a vegetable, and once a day they have chicken. Some in the Middle East say they drink less water at their desert worksites than they do in mountainous Nepal because, as Hindus, they're not allowed to use Muslim bathrooms and are forced to wait for hours.

No one has identified a single cause of SUNDS fatalities — medical journal discussions include genetics, infection and nutritional deficiencies. And in Nepal, the syndrome is not being considered at this point. Instead, Nepali authorities say it could be stress, even homesickness, brought on by physically demanding jobs in extremely hot climates.

Utah State University professor Ron Munger studied heart scans of migrant workers in Thailand after hundreds died in their sleep in Singapore, where they had gone for jobs. He said the Nepali deaths "sound like exactly the same thing."

While the causes of the previous strings of deaths have never been pinpointed, the number of fatalities dropped in each case when workplace safety, housing and diet were improved.

"It's tragic and terrible, and for me this is personal," said cardiac epidemiology researcher Nirmal Aryal, a Nepali native at University of Otago in Wellington, New Zealand.

He recently published a "Call for Public Health Action" in the Asia-Pacific Journal of Public Health, demanding with colleagues in the United Kingdom and Nepal that universal labor laws be enforced and accurate mortality records kept. He's forming a consortium to investigate migrant deaths across borders. Its first focus, in 2017, will be on workers from Nepal.

"It's critical we find out what is happening," he said.

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Arriving in their village, Saro steps out of the truck, sees the coffin and falls screaming onto the dusty road. Two sisters scoop her up and carry her, howling, into the family home.

In Hindu mythology, if you don't see the face of a loved one, you will not believe they have died. And so villagers cram around the coffin while an elder pulls the white wrap off Balkisun's face. Saro, sobbing and screaming, is shoved forward to look.

Someone pours water over Saro's hair, rinsing out the red tikka powder, which is only allowed for married women. The priest breaks the glass bangles on her wrist into the coffin — those too are for married women.

Saro isn't allowed to remarry. She will probably live on the edges of society, earning nothing more than some food to eat and a place to sleep.

"Where's my dad?" asks her 3-year-old son, Siban, perched on the shoulders of a stocky uncle.

About 50 men from the village bring Balkisun's body on a freshly cut bamboo platform to the river chanting, "The name of Ram is the supreme truth." Soon, the boy will be purified, dipped naked in the river. He will be wrapped in white cloth. And with his uncles' hands guiding his own, he will take a bundle of burning twigs and light his father's funeral pyre.

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Associated Press journalists Binaj Gurubacharya, Niranjan Shrestha and Janak Raj Sapkota in Nepal, Eileen Ng in Malaysia and Adam Schreck in United Arab Emirates contributed to this story.

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