Britain's Health Protection Agency has published an early genetic sequence of the new respiratory virus related to SARS that shows it is most closely linked to bat viruses, and scientists say camels, sheep or goats might end up being implicated too.
So far, there are no signs the virus will be as deadly as SARS, or severe acute respiratory syndrome, which killed hundreds of people, mostly in Asia, in a 2003 global outbreak.
In Geneva, WHO spokesman Glenn Thomas told reporters Friday that so far the signs are that the virus is "not easily transmitted from person to person" - but analyses are ongoing.
Global health officials suspect two victims from the Middle East may have caught it from animals.
"It's a logical possibility to consider any animals present in the region in large numbers," said Ralph Baric, a coronavirus expert at the University of North Carolina at Chapel Hill. "Biologists now need to go into the area and take samples from any animals they can get their hands on, including camels and goats," he said. Baric said it was crucial to find out how widespread the virus is in animals and what kind of contact might be risky for people.
Baric suggested bats might be spreading the virus directly to humans since the two confirmed infections happened months apart. "If there was an established transmission pattern from other animals, we probably would have seen a lot more cases," he said.
The World Health Organization said it is considering the possibility the new coronavirus sickened humans after direct contact with animals. The agency is now working with experts in the Middle East to figure out how the two confirmed cases got infected but could not share details until the investigation was finished.
One patient was a Saudi Arabian man who died several months ago while the other is a Qatari national who traveled to Saudi Arabia before falling ill and is currently in critical but stable condition in a London hospital.
Earlier this week, WHO issued a global alert asking doctors to be on guard for any potential cases of the new respiratory virus, which also causes kidney failure.
Saudi officials have already warned that next month's annual Muslim Hajj pilgrimage, which brings millions to Saudi Arabia from all around the world, could allow the virus to spread. As a precautionary measure, they are advising pilgrims to keep their hands clean and wear masks in crowded places.
Experts said knowing where a virus comes from provides clues on how to stop it.
"This means we could prevent the fire before it starts instead of rushing towards it with fire trucks and water hoses afterwards," said Michael Osterholm, an infectious diseases expert at the University of Minnesota.
Osterholm said it was possible bats had simply passed on the virus from other animals and that there could be a complicated transmission chain that ultimately ended in humans.
Viruses reproduce as they infect animals and people, giving them more chances to evolve into a deadlier version.
"We don't know enough about coronaviruses to predict which mutations might make them more lethal or transmissible," Osterholm said. "But you don't want to tempt genetic fate with microbes because you're bound to lose most times."