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SARS Fears Growing in U.S.

4 in 10 Americans Worried About SARS

Is the SARS Virus Mutating?

Experts say coronaviruses, such as the virus that causes SARS, are single-stranded RNA viruses that are known for their propensity to change and evolve. Some researchers have suggested that the SARS virus may be mutating and forming more virulent strains, which might explain why some people with SARS develop a potentially deadly illness and others recover.

If the virus is indeed changing and mutating, it would make efforts to develop a vaccine or other treatments for SARS much more difficult.

"If we are going to use a vaccine or antiviral strategy for SARS, it is important to know about these genetic changes and what they mean in terms of biological significance," says Albert D.M.E. Osterhaus, DVM, PhD, a professor at the Institute of Virology at Erasmus University in Rotterdam, Netherlands.

Osterhaus was the leader of the research team that provided the conclusive evidence based on animal testing that a previously unknown coronavirus was indeed the cause of SARS. He says it's still too soon to say what might causing subtle genetic differences found in the newly discovered SARS virus in samples from different SARS patients.

"It is still hard to say what the mutations mean," Osterhaus tells WebMD. "Whether these mutations represent escape variants or differences in individual patients' immune response to the virus, we don't yet know."

CDC Director Julie Gerberding, MD, says although researchers moved with unprecedented speed in isolating and sequencing the SARS virus, there is still much more work to be done.

"I'd love to know why some patients are sicker than others, and why in some populations there seems to be a higher attack rate of the pneumonia in others, but it's just really preliminary I think to ascribe that to the virus, per se. We have a lot to learn," says Gerberding.

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