A deadly new SARS-like virus has been traced to bats.
The Middle East Respiratory Syndrome, or MERS, has proven lethal in 60 percent of cases identified so far.
A new study has found the virus is carried naturally by a type of bat in Saudi Arabia, ground-zero for the disease.
"We don't know how it leapt into humans," says Ian Lipkin, who co-authored the study. "But there are several possibilities."
Lipkin is professor of epidemiology at Columbia University's Center for Infection and Immunity.
One possibility is that dried infected bat guano could have been inhaled directly by the first victim.
Another is that it could have been transmitted through another animal, such as a rodent or domestic animal.
The bat under study eats only insects and does not bite humans.
MERS has been transmitted from person to person, but so far only after prolonged intimate contact, such as between family members and care givers.
Commenting on the high mortality rate, Lipkin says that's quite common in new diseases, since the statistics are skewed by the fact that only the most serious cases are correctly identified in a disease's early stages. Many people who only get mild symptoms are not identified, while some of those infected may be entirely asymptomatic.