It's called Middle East respiratory syndrome, or MERS, after the region where almost all the patients have been reported. But the name may turn out to be a misnomer. A new study has found the virus in camels from Sudan and Ethiopia, suggesting that Africa, too, harbors the pathogen. That means MERS may sicken more humans than previously thought—and perhaps be more likely to trigger a pandemic.
MERS has sickened 183 people and killed 80, most of them in Saudi Arabia. A couple of cases have occurred in countries outside the region, such as France and the United Kingdom, but those clusters all started with a patient who had traveled to the Middle East before falling ill.
Scientists have uncovered more and more evidence implicating camels in the spread of the disease. They found that a large percentage of camels in the Middle East have antibodies against MERS in their blood, while other animals, such as goats and sheep, do not. Researchers have also isolated MERS virus RNA from nose swabs of camels in Qatar, and earlier this week, they showed that the virus has circulated in Saudi Arabian camels for at least 2 decades.
Malik Peiris, an infectious disease researcher at the University of Hong Kong, and colleagues expanded the search to Africa. In a paper published last year, they showed that camels in Egypt carried antibodies against MERS. For the new study, they took samples from four abattoirs around Egypt; again they found antibodies against MERS in the blood of 48 out of 52 camels they tested. But the most interesting results came from taking nose swabs from 110 camels: They found MERS RNA in four animals that had been shipped in from Sudan and Ethiopia.
Peiris cautions that it is unclear whether the infected camels picked up the virus in Sudan and Ethiopia or on their final journey in Egypt. Abattoirs could help spread MERS just like live poultry markets do for influenza, he says. "You cannot point the finger exactly at where those viruses came from," he says. "But I would be very surprised if you do not find the virus in large parts of Africa."
If so, that changes the picture of MERS considerably. No human MERS cases have been reported from Egypt or anywhere else in Africa, but if camels are infected, they may well occur, says Marion Koopmans, an infectious disease researcher at Erasmus MC in Rotterdam, the Netherlands. "It would be important to look systematically into that," she writes in an e-mail. "Health authorities really need to test patients with severe pneumonia all across Africa for MERS," Peiris says.
The researchers were able to sequence the virus of one of the camels almost completely, and it is more than 99% identical with viruses found in people. "I would be very surprised if this virus cannot infect humans," says Christian Drosten, a virologist at the University of Bonn in Germany. But the virus also shows a few intriguing differences from known camel samples, he says. "We have to analyze this carefully in the next few days, but it looks like this sequence broadens the viral repertoire found in camels," he says. If the viruses found in camels show more genetic variation than those isolated from humans, that is further strong evidence that camels are infecting humans and not the other way around.
Anthony Mounts, the point person for MERS at the World Health Organization in Geneva, Switzerland, says that it is very likely that human MERS cases occur in Africa. "Wherever we find [infected] camels, there is a good chance we'll find [human] cases if we look closely," he says. And humans may be exposed to camels in Africa much more often than in the Middle East: There were about 260,000 camels in Saudi Arabia in 2012, but almost a million in Ethiopia and 4.8 million in Sudan, according to the U.N. Food and Agriculture Organization. The more human cases there are, the higher the risk that the virus will one day learn how to become easily transmissible between people, which could set off a pandemic.
The researchers also looked at the blood of 179 people working at the camel abattoirs for antibodies against MERS virus, but found none. That shows that the virus is only rarely successful in infecting human beings, Peiris says. "What we need to find out now is the reason for these rare transmissions."