FRIDAY, Sept. 20 (HealthDay News) -- A deadly respiratory virus in Saudi Arabia is centered around the capital city of Riyadh and has been transmitted from animals to humans more than once, genetic analyses show.

Researchers analyzed the genomes of Middle East respiratory syndrome (MERS) viruses collected from 21 different patients in different regions of Saudi Arabia. The results showed that MERS is focused around Riyadh, with sporadic cases in other areas.

More virus genomes, however, will have to be analyzed to more firmly establish the locations involved, the researchers said.

The researchers also found that a single transmission of the MERS virus between animals and humans is unlikely. Instead, it appears that the virus has been transmitted from animals to humans on several occasions, as well as being transmitted between people.

The results revealed that considerable time has passed since the viruses analyzed in the study shared a common ancestor. This lends support to the theory that the MERS virus might be transmitted to humans by an intermediary animal host, according to the authors of the paper published in the Sept. 20 issue of the journal The Lancet.

An ancestor of the virus has been found in bats, and signs of the virus have been found in camels. However, no animal "reservoir" for the virus has been definitively identified. Further animal studies are needed to pinpoint where the virus is coming from, the researchers said.

One expert said efforts to understand this new virus have been ongoing.

"Since the first case of infection with the Middle East respiratory syndrome coronavirus was reported from Saudi Arabia in the spring of 2012, there has been concern about the potential for this virus to cause a pandemic such as was seen with SARS in 2002 and 2003," said Dr. David Hill, director of the global public health program at Quinnipiac University in Connecticut.

"Thus, there have been extensive efforts to characterize the virus, to determine where it exists in the environment -- that is, where it came from, whether it can be transmitted from human to human and, if so, how easily can the virus be transmitted?" Hill said.

"The answer to the latter question is that the virus can be transmitted between humans, usually in family or health-care settings, but not very easily," he added.

"The good news is that even after millions of persons gathered in close proximity to each other in Saudi Arabia for the pilgrimages for Hajj and Umrah, there were no cases of MERS [coronavirus] infection," Hill said. "The risk for acquiring MERS [coronavirus] remains extremely low for those traveling to the Middle East. However, common-sense precautions should be exercised: avoid close contact with persons who have respiratory infections and wash [your] hands on a frequent basis."

More information

The U.S. Centers for Disease Control and Prevention has more about MERS.