In contrast, younger camels were more likely to have active virus (35 percent of young camels had active virus in their nasal samples, compared to 15 percent of adult camels).
These finding suggest that, for camels, MERS infection "typically occurs in early life, and that if people get the virus from camels, the most likely source is young camels," study researcher Dr. W. Ian Lipkin of Columbia University, New York, said in a statement.
The archived blood samples also contained MERS antibodies, suggesting the MERS or a similar virus has been circulating in camels for at least two decades.
Previously, the researchers found that camels had antibodies against the MERS virus, and that some were infected with active virus. The new study is the first to perform a countrywide survey of camels in Saudi Arabia.
However, the new study does not prove that humans caught the virus from camels, and more studies are needed to rule out other possibilities. For example, it could be that another animal infects both humans and camels. The MERS virus has also been found in bats.