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Sources of MERS Still Unknown

As the death toll rises, scientists scour the Middle East respiratory syndrome coronavirus genome for clues as to how it first infected humans.

By | September 23, 2013

FLICKR, NIAIDThe World Health Organization last week announced 18 new laboratory-confirmed cases of Middle East respiratory syndrome coronavirus (MERS-CoV) infection, including three deaths. From September 2012 to date, the CoV has infected 132 people worldwide, killing 58 of them. As scientists continue to investigate the etiology and epidemiology of MERS, others are scouring the CoV genome for clues to its deadly potential and how it first infected humans.

In a report published last week (September 20) in The Lancet, researchers from the Saudi Arabian Ministry of Health and their international colleagues examined the viral genomes from 21 MERS cases, and analyzed the phylogenetic relationships among them, plus nine already published MERS-CoV genome sequences. Their analysis hinted at multiple chains of infection in humans, suggesting that in one particular outbreak—the Al-Hasa cluster—the MERS-CoV might have been introduced to people more than once. Further, the researchers found evidence to suggest that additional human or animal cases, which have gone undetected to date, may be sources of infection.

“The hypothesis now is [that] there were multiple introductions into the hospitals from the community, which gives us the clue that there is probably a community source of transmission,” the Ministry of Health’s Ziad Memish told NPR’s Shots blog. “My gut feeling is [that] there is some animal reservoir that is causing the transmission that is still to be found,” he added.

Nevertheless, “the source of the virus and mode of disease transmission remain unknown,” The Chinese University of Hong Kong’s David Hui noted in a Lancet commentary accompanying the genomic analysis. While researchers in August reported having isolated a small stretch of viral sequence in a bat that was nearly identical to that from the first human infection case, the finding has yet to be replicated. Others have also reported finding MERS-CoV neutralizing serum antibodies in dromedary camels. Still, neither bats nor camels are confirmed animal reservoirs.

Indeed, in The Lancet paper, Memish and his colleagues noted that “transmission within Saudi Arabia is consistent with either movement of an animal reservoir, animal products, or movement of infected people,” adding that “further definition of the exposures responsible for the sporadic introductions of MERS-CoV into human populations is urgently needed.”

That scientists are not yet sure of the source(s) of MERS has irked some. “We should have had this kind of information long ago,” the University of Minnesota’s Michael Osterholm, director of the Center for Infectious Disease Research and Policy, told NPR. “The fact that we have such incomplete information a year into this is just inexcusable.”

But Memish assured Shots that he and his colleagues are now working night and day to find potential animal reservoirs and previously unrecognized human-to-human cases that may be causing MERS to spread. “It won’t be too long before we find out what’s going on,” he told NPR.

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Mettler Toledo
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