Dr. Michael Lai, a coronavirus expert at the University of Southern California, said the structure of the SARS virus genetic makeup shows some similarity to bird coronaviruses, but not known examples from chickens or other animals.
So that makes him speculate the virus came from a wild bird, he said. People in southern China, where the SARS epidemic began, like to capture wild animals for food, so maybe that's how the virus made the jump to humans, he said.
The lack of antibodies to the virus in healthy people tested so far makes him think the virus hasn't had much time to get around, suggesting the transfer from animals came in the last year or so, he said.
Francois Meslin, who coordinates a WHO team in Geneva that deals with diseases that can jump to humans from animals, said as yet there's no evidence SARS came from animals.
So far, scientists are just exploring the feasibility of such research. At the same time, the WHO also plans further epidemiological work in China, looking for clues that link early cases to animals, farms or the slaughtering or butchering of animals, he said.
As it stands right now, in trying to figure out what animals to include in the exposure study, he said, "we are totally working in a vacuum, since we have no epidemiology link."
In any case, he said, finding the answer may be complex. One species may be the reservoir in nature that harbors a virus over a long period of time, but the virus may have to pass to a second species that has more contact with humans before people get infected. That's the case with Ebola virus, which humans can pick up from ill or dead chimps but for which the ultimate reservoir is unknown, Meslin said.
"The cycle can be quite com-plex," he said. "If SARS is something that is deep inside a very complex cycle involving a rare reservoir species, we may never get to it."
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