Soaring MERS Cases in Saudi Arabia Raise Alarms

Science  02 May 2014:
Vol. 344, Issue 6183, pp. 457-458
DOI: 10.1126/science.344.6183.457
Game changer.

Worried about MERS, workers wear facemasks at a 22 April soccer match in Riyadh.


Scientists are scrambling to make sense of a sharp increase in reported infections with the deadly Middle East respiratory syndrome (MERS) virus. In April alone, Saudi Arabia and the United Arab Emirates have reported over 200 new cases—more than all MERS-affected countries combined in the preceding 2 years. That has sparked fresh fears that the virus may be about to go on a global rampage.

The World Health Organization expressed alarm at the new numbers, and the European Centre for Disease Prevention and Control (ECDC) published an updated risk assessment on 25 April warning European countries to expect more imported cases. Saudi Arabia, meanwhile, replaced its health minister.

The surge has raised concerns that the virus is undergoing genetic changes that might cause it to become pandemic. But none have been identified so far, and several other factors could be to blame, scientists say—from increased testing to sloppy hospital hygiene and a wave of camel births across the region.

Saudi Arabia alone has now reported 345 MERS cases, including 105 deaths, since the start of the epidemic in 2012; most of the new cases are in Jeddah, in the western part of the country. Many worry that mutations in the virus's genome might be making it more adept at spreading between humans—as happened with MERS's distant cousin, severe acute respiratory syndrome (SARS), in 2002 and 2003.

To explore that possibility, virologist Christian Drosten of the University of Bonn in Germany is collaborating with Saudi Deputy Minister of Health Ziad Memish. On 18 April, Drosten's lab received 31 samples taken from Jeddah patients; 29 had tested positive for MERS in two separate PCR tests in a local lab. Drosten's team confirmed the diagnosis for 28 of the samples, suggesting that false positive results—which occur easily with PCR—aren't the problem.

On 26 April, the lab finished sequencing three viral genomes and quickly posted them on the Internet. "These sequences look completely normal," Drosten says. "There is no reason to assume they have acquired changes increasing their pandemic potential."

Memish believes the main cause for the surge is increased testing, triggered by growing media attention to MERS. Until recently, only patients with pneumonia who needed intensive care were tested for the virus, he says. "But because of the media hype, people have started coming into emergency rooms and hospitals complaining of mild fever or a cough, demanding to be tested." Doctors have complied, Memish says, leading to more diagnoses, especially of mild cases. Drosten, who was in Riyadh early this week, confirms that the city is on edge: "You see people walking around with facemasks now," he says.

But Denis Coulombier, head of surveillance and response at ECDC, notes that "the proportion of symptomatic to asymptomatic cases is in line with what we have seen previously, so changes in testing do not fully explain the increase we see in April." And Bart Haagmans of Erasmus MC in Rotterdam, the Netherlands, says that it is hard to tell from a sequenced genome whether the virus has undergone adaptive changes. Even in influenza, one of the most studied pathogens in the world, scientists hardly know what mutations to look for, he says.


Drosten believes an additional reason for the spike may be a lack of hygiene in the worst affected hospital in Jeddah, which would help the virus spread between patients and health care workers—although it's unclear exactly what the hospital is doing wrong.

Camels may also play a minor role in the explosive rise. Scientists have shown that many dromedary camels in the Middle East and Africa harbor the virus, and in recent months, camels at breeding facilities have given birth en masse, as they do every winter. The offspring may act as natural virus incubators, increasing the risk that humans become infected.

Drosten's data reinforce the idea that MERS is repeatedly crossing the species barrier between camels and humans, says evolutionary biologist Andrew Rambaut of the University of Edinburgh in the United Kingdom. The three genomes Drosten posted this past weekend are most closely related to one isolated from a Qatari patient who was treated in England in September 2012, Rambaut says. There is no known connection between the cases in Qatar and Jeddah, and given that so many camels are infected, it is much more likely that a virus with this sequence crossed to humans twice—once in Qatar and again at the start of the Jeddah cluster—than that the virus passed through a chain of unknown human patients, he says.

Such jumps from camels to humans "will just continue happening until the exposure to camels is reduced," Rambaut says. The question is how to do that, because it's unclear how the virus crosses from camels to humans. One route could be unpasteurized camel milk, consumed widely in the Middle East; scientists at the U.S. National Institute of Allergy and Infectious Diseases recently showed that the virus is stable for at least 72 hours in raw camel milk. Haagmans hopes to test camel urine and milk from the region for the virus soon. Contaminated meat could also play a role. Another, less likely possibility is that the virus is transmitted through the air. Virus excreted by camels could cling to dust particles, for instance, and infect humans who inhale it.

Some answers may come from Qatar. Researchers there have teamed up with Marion Koopmans and other scientists at Erasmus MC for the biggest study by far of how MERS spreads. The team plans to sample camels and other animals, as well as humans, at about 500 farms to look for the virus and antibodies against it; 80 people have been trained to question farm workers in detail about their behavior, and Koopmans says she has shipped more than 45,000 labels for samples to Qatar. "We really have to step up our efforts to understand what is going on," she says.


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