Camels have been implicated in a Middle Eastern respiratory syndrome known as MERS, a viral infection that has caused outbreaks in humans in that part of the world, a new study suggests.

As of April 23, 345 laboratory-confirmed cases, including 107 deaths, have been linked to the coronavirus and reported to public health authorities worldwide, according to the European Centre for Disease Prevention and Control.

More than 60 cases, or about a quarter of the global total since MERS was identified, have been reported in the past month, the American Society for Microbiology says.

Now scientists have grown the virus from nasal swabs of two dromedaries in Saudi Arabia, genetically sequenced it and found it was an "indistinguishable" match to MERS coronavirus found in humans — an indication that the virus in the animals is capable of infecting humans.

"Together with data indicating widespread dromedary infection in the Kingdom of Saudi Arabia, these findings support the plausibility of a role for dromedaries in human infection," Thomas Briese, associate director of the Center for Infection and Immunity at Columbia University in New York and his co-authors concluded in Tuesday’s online issue of the journal mBio, published by the American Society for Microbiology.

The finding strengthens the argument that the camels are a reservoir for the virus, Briese said.

"We have evidence going back as far as the early 1990s that this virus has been in camels. Human cases didn't start till 2012. So one very important question is what happened that caused this virus to cause severe disease in humans, noticeable disease in humans for the first time in 2012?" said Dr. Allison McGeer, an infectious disease specialist at Toronto’s Mount Sinai Hospital who has helped investigate the new virus in Saudi Arabia as part of a World Health Organization-led team.

Veterinarian Dr. Ehab Al-Shabori in Riyadh said everything is normal among camels.

"If it were risky or there were any problems, we would have received an alert or brochures," Al-Shabori said in Arabic to Reuters. "We would have witnessed cases infected with coronavirus. But there is nothing."

If the infections were coming directly from the camels, you would expect disease in the people who work more closely with camels, but that’s not what scientists are seeing, McGeer said.

"So you can speculate about a number of different explanations for why it's true, but we clearly need to understand what's happening and how it's happening."

Camel precautions

The majority of cases now in Saudi Arabia are not linked to camels, but are associated with person-to-person transmission in hospitals, McGeer said. "Continuing transmission in hospitals is a concern. It's just not possible to tell from the data we have what's driving that."

Seventy-two of the 345 cases have been health-care workers, the European CDC said.

As for the recent spike in cases, several theories have been proposed, including a potential seasonal explanation. Like cows, camels give birth in the spring. Viral nucleic acid has been detected more in juvenile dromedary camels, the study’s authors said.

"The theory is that camels are being born, there's more infection in baby camels and so the risk is higher. That's a great theory. It just might not be true," McGeer said.

As a precaution, health authorities such as the Public Health Agency of Canada are advising people to avoid contact with direct and indirect contact with camels, including unpasteurized camel milk.

The World Health Organization says there’s no need for travel restrictions. It’s recommended that all countries enhance surveillance to detect any cases of severe respiratory illness quickly and test them.

"We're much better off not having a travel ban but making sure that all of us in Canada are ready for the first case, able to deal with it and going to manage it properly," McGeer said.

A team of eight WHO staff members are currently in Saudi Arabia working with the health ministry and other partners to get a better understanding of the virus and to look at recent outbreaks in health-care facilities in Jeddah, spokesman Tarik Jasarevic said in an email. They are also trying to determine what's the best public health advice to give people.

With files from CBC's Kas Roussy