The MERS coronavirus that has now infected nearly 200 people is widespread in camels across Saudi Arabia — and may have circulated in the animals for at least two decades before first appearing in humans, a new study has found.

The study, published on Tuesday by the journal mBio, strengthens the theory that camels could be spreading MERS, a deadly new virus that first emerged in the Middle East and has now infected 182 people and killed 79.

It also finds that most camels are probably catching the virus at a young age. In Saudi Arabia, most camel births take place between November and January — meaning there is now a fresh batch of newborn camels that could soon become infectious, German virologist Dr. Christian Drosten said in an email.

“This suggests we have to expect a stark increase of new human cases in the weeks to come,” said Drosten, who has studied MERS in camels but was not involved with this paper. “Those new young camels born this winter will all be infected during the coming weeks or few months. And they will spill their virus to humans.”

MERS, which stands for Middle East respiratory syndrome, was first detected in 2012 but investigators still have no idea how people are catching the virus. So far, the virus does not seem to spread easily between people, and a leading theory is that it originally came from bats but can also infect camels — which are now spreading the virus to humans somehow.

Previous studies have found strong evidence of MERS in both bats and one-humped camels. But the mBio paper is the most comprehensive investigation yet into camels in Saudi Arabia, where the majority of human MERS cases have occurred.

Because camel samples are difficult to import into the United States, scientists from New York’s Columbia University built a “mobile lab” that they sent to Saudi Arabia. There, Saudi scientists spent two months collecting blood, nasal and rectal samples from more than 200 one-humped camels across the country, as well as from goats and sheep.

“It’s not easy to take samples from the camels,” said the study’s first author, Abdulaziz Alagaili, a mammalogist with King Saud University and the Saudi Wildlife Authority. “They are huge animals. Especially with the old ones, it’s hard to tie the camels and draw the blood from the leg.”

The researchers found no sign of MERS in the goats or sheep. But 74 per cent of camels had antibodies in their blood — meaning they were previously infected with either MERS or another closely related virus.

Old blood samples were also taken out of storage and researchers found antibodies in camels dating back to 1992.

“It’s to show that this is not necessarily a new virus,” said Dr. Juan Lubroth, the chief veterinary officer with the UN Food and Agriculture Organization, who was not involved with the study. “It’s been around for a long time.”

But the study’s authors also tested for genetic evidence of the virus — a sign of recent infection and more conclusive evidence that camels can catch MERS.

Again, they found positive results in camels across the country — but mostly in the nasal swabs and in camels under the age of two. This both suggests that younger camels are more infectious and that the virus is most likely spread further by “airborne transmission.”

The genetic code revealed the camel coronavirus was “the same virus that has been infecting people,” said Dr. Ian Lipkin of Columbia University, the senior author on the paper.

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“We can say unequivocally that this coronavirus, the same virus that’s been found in humans, is ubiquitous in Saudi Arabia,” Lipkin said. “There is ample opportunity for people to become exposed to the virus by contact with young camels, either directly or indirectly.”

The ultimate proof that camels can be infected by MERS is to “isolate” the virus from a camel — meaning, to find the live virus and grow it in a lab. Nobody has yet reported doing so in a scientific paper but Lipkin said his team has now isolated MERS from two camels.

For Dr. Marion Koopmans, chief virologist with the Dutch National Institute of Public Health, the mBio paper provides enough “proof that (MERS) is a camel virus.” But it does not answer the most crucial question: how are people catching it?

“Is it through direct animal contact? Is it indirect, or an environmental contamination? Is there still another host?” Koopmans asked. “Many people handle camels and do not get sick . . . there’s still a bit of a puzzle there.”

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