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"Influenza is thought not to be a very effective bioterrorism agent because it can't be targeted toward a specific population and can't be contained," he said. "It would spread, including to the terrorist's own population."

There is always the danger that improper handling in a laboratory setting could accidentally unleash a virus into the air. Schaffner said that happened with SARS (severe acute respiratory syndrome), the disease that caused about 750 deaths around the world earlier this decade.

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Viruses regularly change forms, and H5N1, while it doesn't affect humans much right now, certainly has the capacity to do so.

"Viruses can change from season to season and can become more or less virulent, and there's definitely a concern that H5N1 will mutate to a form that can infect humans," said Dr. Maria Alcalde, assistant professor of infectious diseases at the University of Miami's Miller School of Medicine.

Despite the warnings about Fouchier's research, Schaffner said what happens in the lab doesn't always happen outside it.

"It's scientifically conceivable and it's an interesting lab phenomenon, but in nature, it doesn't look as though it could happen," he said. "There's no immediate public health importance."