It may be new to humans, but it appears that the MERS virus or a close cousin may have been infecting camels in parts of the Middle East for at least a decade.
A new study posted online on Thursday provides the first evidence that MERS or a MERS-like virus has been spreading in camels in parts of the region since at least 2003.
The research shows that stored blood samples taken from camels in the United Arab Emirates all contain antibodies to something close enough to MERS that antibody tests designed for MERS detect them.
The first known human cases of the disease occurred in Jordan in April, 2012. To date there have been about 177 human MERS infections identified; 75 of them have been fatal.
As is often the situation with the puzzling virus, the discovery raises at least as many questions than it answers.
“It surely gives us reason to believe that … camel infections could be a very important source of human infection,” said Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.
“But I think the question we have to answer now is how do you reconcile the 2003 data with what appears to be the relative absence of cases back then?”
Osterholm suggested there are three possible scenarios:
– There were no human cases from 2003 to 2012, which would suggest a precursor virus changed to be able to infect people.
– There were earlier cases, but they went undetected.
– There were earlier cases, but fewer of them and a change in the virus prompted an uptick in the pace of human infections.
The World Health Organization’s lead scientist on MERS leans towards the third explanation.
Dr. Anthony Mounts said analysis of the available genetic sequences of MERS point to an emergence of the human virus around mid-2011. That would suggest the antibodies from 2003 might be to a virus that was an ancestor of the current MERS, but not exactly the same virus.
“There could have been infections from that virus in humans going way back that were just never seen—but not commonly enough that they showed up on anybody’s radar,” Mounts said.
“The one that’s now been jumping into humans is a newer development. So it’s a new descendent of that virus that is now transmissible…. That’s what it (the camel data) seems to be saying.”
The study was done by scientists from Germany, the Netherlands and UAE. It will be published in the April issue of the journal Emerging Infectious Diseases, but was posted online on Thursday.
The researchers tested 651 stored camel blood samples. Most of the animals—97 per cent—had antibodies to the virus.
The lion’s share of the samples were drawn in 2013. But 151 had been in cold storage since 2003 and of those, all tested positive for MERS antibodies.
“Dromedary camels from the United Arab Emirates were infected at high rates with MERS-CoV”—CoV is short for coronavirus—”or a closely related, probably con-specific, virus long before the first human MERS cases,” the authors wrote in their article.
The senior author, Dr. Christian Drosten of the University of Bonn in Germany, was not immediately available to comment on the paper.
But Drosten has said for some time that he believes MERS has been around for longer than it has been recognized.
In a recent interview, Drosten said the virus may have been infecting people in the Middle East for decades, but has gone unnoticed.
“These are countries where physicians are used to seeing cases of severe, acute pneumonia with fatality without them noticing something irregular,” he said.
Pneumonia can be triggered by a number of viruses and bacteria and the culprit is not always identified.
The world learned of the existence of the new virus in September 2012. It is a coronavirus, from the same family as the virus that ignited the 2003 SARS outbreak.
It’s thought the virus probably originated in bats. In fact, last summer scientists reported finding an RNA fragment that was identical to MERS in a Egyptian tomb bat in Saudi Arabia, near where an early human case lived. But the fragment was too small to be 100 per cent certain of a perfect match.
People typically don’t have a lot of contact with bats, so the question of how a bat virus is infecting people has preoccupied scientists working on MERS.
Studies have focused on camels, and it is now clear that the animals can be infected by MERS. Camels from Oman, the Canary Islands and Egypt have been found to carry antibodies to the virus (or a close relative). And recently, some of the scientists who worked on this new paper reported finding MERS virus in camels from Qatar.
It remains to be seen, though, whether camels pass the virus to people or if some other species is playing that role.
The study also reported that 16 camels in German zoos were tested for MERS antibodies. None of the animals tested positive. The authors say that could be because the camels in Germany were from a different species of camel, or it could suggest the MERS virus is only present in a restricted geographic area.