MERS May be Transmitted by Camel

Ever since people in the Middle East started dying of a mysterious new infection last year, scientists have been trying to pinpoint the source of the outbreak. Now they may finally have found a clue in an unlikely population: retired racing camels.

The Middle East respiratory syndrome (MERS) virus has sickened 94 people so far and killed 46 of them. While some patients have clearly been infected by others, there are also cases who have been nowhere near a known patient. So scientists suspect that one or more animal species harbor the virus and are transmitting it to people.

Like severe acute respiratory syndrome (SARS), MERS belongs to the coronaviruses, a group of viruses thought to originate in bats. Indeed, researchers investigating the new pathogen have found a closely related virus in bats in South Africa, and they have been able to grow the MERS virus in various bat cell lines. But direct infection by bats is unlikely because humans have very little interaction with them. Instead, researchers suspect that there is an intermediate host.

Now, an international team of scientists has tested the blood of various livestock species, including cattle, sheep, goats, and camels from the Netherlands, Spain, Chile, and Oman. They also tried to get samples from countries that have had human MERS cases, such as Saudi Arabia and Qatar, says Marion Koopmans, an infectious disease researcher at the National Institute of Public Health and the Environment in the Netherlands and one of the authors of the paper. But none of those countries cooperated.

To find out if the animals had been exposed to the MERS virus, the team screened the blood for antibodies against part of an important protein called spike on the viral surface. In order to ensure that the antibodies were specific to MERS, the scientists also tested the spike proteins of SARS and OC43, a human coronavirus closely resembling one circulating in cows, sheep, goats, and camels.

As expected, several animals had antibodies against OC43 in their blood, and none carried antibodies against SARS. But 50 dromedary camels from Oman that were tested all had antibodies against the MERS virus, the scientists report today in The Lancet Infectious Diseases. (This link will be live after 6:30 pm U.S. Eastern time.) "There is something circulating in dromedary camels that looks very much like MERS coronavirus," Koopmans says. The camels are all female retired racing camels used for breeding, but they belong to different owners in separate locations.

"That's a really important paper," says coronavirus researcher Matthew Frieman of the University of Maryland School of Medicine in Baltimore. "The fact that 100% of the Omanian camels are positive means that the result is highly significant and likely very real." Ian Lipkin, a virologist at Columbia University who's also searching for MERS in animal samples, says that the paper provides "compelling evidence that camelids [a group that includes camels, llamas, and alpacas] may be implicated." But the search for other hosts needs to continue, he adds.