A farm in Qatar might hold the clues that link the emerging Middle East respiratory syndrome (MERS-CoV) to camels.
For the first time, the virus has been isolated from a non-human species -- camels on a small farm that is also linked to two human cases, according to Marion Koopmans, DVM, PhD, of Erasmus Medical Center in Rotterdam, and colleagues.
The finding is the result of an intensive epidemiological investigation that began after the Qatar health ministry reported in October that two men -- the farm's owner and a worker -- had laboratory-confirmed MERS-CoV, Koopmans and colleagues reported online in The Lancet Infectious Diseases.
MERS-CoV is a betacoronavirus found in bats, but many of the same investigators earlier found hints that it might also infect camels.
"This is definitive proof that camels can be infected with MERS-CoV," the researchers said in a statement.
What remains unclear is whether -- or even if -- the virus passed from camels to humans or vice versa, the researchers reported.
Aside from the possibility of direct transmission, it's also possible "that humans and camels could have been infected from a third as yet unknown source," they wrote.
"The big unknown is the exact timing of infections, both in the persons and in the camels," they said.
Pinning down the role of animals in the transmission of the virus will be important for control efforts, commented Neil Ferguson, FMedSci, and Maria Van Kerkhove, PhD, of Imperial College London in England.
If it turns out that sustained transmission from humans to humans is not yet happening, "measures targeting affected animal species and their handlers might eliminate the virus from the human population," they argued in an accompanying commentary.
On the other hand, if the virus is now mainly being transmitted among people, "even intensive veterinary control efforts would have little effect," they concluded.
Koopmans and colleagues began their investigations within a week of the Oct. 13 diagnosis of the first case, the farm's 61-year-old owner. The 23-year-old farm worker was diagnosed 4 days after the first man.
With the assistance of experienced camel wranglers, the investigators took nasal and rectal swabs, as well as blood samples from the 14 camels on the farm.
Genetic analysis showed that MERS-CoV was present in three of the animals, the researchers reported, but all 14 had antibodies to the virus.
Analysis of three regions of the virus showed the genetic sequence isolated from the infected animals was similar to that found in the two men, but was not completely identical.
The difference, however, was so small that it was not possible to use the information to deduce the direction of transmission, Koopmans and colleagues reported.