Scientists say they are one step closer to understanding the origins of Middle East respiratory syndrome (MERS), the deadly viral disease that has been spreading in the Middle East for more than a year. They have found a small fragment of the virus's genome in an Egyptian tomb bat from Saudi Arabia, suggesting that these bats are a source of the virus—although another animal species may act as the bridge to humans.
Since it was first discovered in 2012, MERS has sickened 97 people and killed 47, most of them in Saudi Arabia. The virus has sometimes been transmitted from one patient to the next, but in most cases the source of infection remains unclear. Epidemiologists have speculated that bats, which are host to several related viruses, could be a reservoir. Scientists just reported finding a coronavirus closely resembling MERS in the feces of a South African bat.
Columbia University virologist Ian Lipkin, whose team has been collaborating with Saudi Deputy Minister of Health Ziad Memish, is one of the few scientists who have had access to animal samples from the region where MERS occurs. In October 2012, Lipkin and other researchers went to the home of the first known MERS patient in Saudi Arabia, a man who died in June 2012 in Bisha, in the country's southwest. They collected blood and tissue samples and throat and rectal swabs from 96 bats captured in an abandoned date palm orchard less than 12 kilometers from the man's home and close to the hardware store where he worked.
Sequencing the nucleic acids isolated from the samples yielded a clue: The fecal pellet of the insect-eating Egyptian tomb bat (Taphozous perforatus) contained a piece of viral RNA identical to that of the virus isolated from the patient in Bisha, the scientists reported online in Emerging Infectious Diseases yesterday.
The researchers didn't isolate the virus itself, and the snippet was only 182 nucleotides long, so the bat may have been infected with another, very closely related virus. The researchers had hoped to find more and longer pieces of the viral genome, but an incident at U.S. customs may have thwarted their efforts. The samples, collected in October 2012, were frozen and transported to Columbia University on dry ice. But customs officers opened the shipment and its contents sat at room temperature for 2 days, thawing all the samples, Lipkin says. "That is probably why we didn't get more sequences out of this."
Still, the finding is another interesting piece in the MERS puzzle, says Marion Koopmans, an infectious diseases researcher at the National Institute for Public Health and the Environment in the Netherlands, who was not involved in the work. She points out that the fragment is not only short but also comes from one of the least variable parts of the viral genome, so the full genomes of bat and human virus could still differ significantly. Nonetheless, the finding "points at bats as a reservoir for this virus," Koopmans writes in an e-mail.
The researchers made the discovery in December 2012 but decided not to publish it right away because they were hoping to find more compelling evidence. Samples from a second investigation in Saudi Arabia in April 2013 did not yield any further clues, however. Lipkin says that he decided to publish the result after the coronavirus finding in a South African bat was reported. The virus from South Africa was more distantly related to MERS, says Andrew Rambaut, a computational biologist at the University of Edinburgh who is also investigating MERS; it had 12 differences within the same 182-nucleotide stretch of RNA.
Lipkin does not think that bats infect humans directly. "There have been so many cases of MERS described in the Middle East where we cannot make a direct link with bats," he says. "So there is likely to be an intermediate host." Two weeks ago, a team that included Koopmans reported finding antibodies against MERS in retired racing camels in Oman, a country that has reported no MERS cases but neighbors Saudi Arabia. But Lipkin is skeptical. "Those results are interesting, but I'm not persuaded that camels are implicated," he says—if only because many MERS patients did not report contact with camels.
Lipkin says that scientists should cast a wider net by testing more animal species—especially cats, dogs, and rodents—that might act as an intermediate host. He says he is discussing further studies with Memish and is preparing staff members to fly to Saudi Arabia within a month.