Called Middle East Respiratory Syndrome, or MERS, it has killed 79 of the 182 people infected since September 2012, according to the World Health Organization.
Until now, little was known about its source or how it could be infecting people.
But senior study author Ian Lipkin of Columbia University said research now shows the virus is "extraordinarily common" in camels and has been for at least 20 years.
"In some parts of Saudi Arabia, two-thirds of young animals have infectious virus in their respiratory tracts," he told AFP.
"It is plausible that camels could be a major source of infection for humans."