Ferrets are used to study influenza because the flu virus affects them in a similar way to humans, the researchers noted.
"One thing we know for sure about influenza viruses is that they are unpredictable," Tumpey added. "The characteristics that the virus is displaying today might not hold true in the upcoming months."
It is important to remember, he said, that this is a new influenza virus never seen in humans before April 2009.
"The virus does not appear to be fully adapted to its new human host," Tumpey said. "How the virus may adapt further as it circulates among people is not known. However, this uncertainty makes it imperative that the virus and the epidemiology of the outbreak be closely monitored."
Dr. Pascal James Imperato, dean of the School of Public Health at SUNY Downstate Medical Center in New York City, found the new research added key information to what was already known.
"In this study, it was found that the 2009 H1N1 virus was less efficiently transmitted by droplet infection in ferrets compared to the seasonal human H1N1 virus," Imperato said. "This is a significant finding as it indicates that the 2009 swine flu virus might not be as easily transmitted between humans as its seasonal counterpart."
On the other hand, he added, the findings also "collectively demonstrate that it has the potential to cause serious clinical illness that also results in gastrointestinal symptoms, which were, in fact, observed in a number of patients."
On June 11, the World Health Organization declared the first flu pandemic since 1968, triggered by the rapid spread of the H1N1 swine flu virus across North America, Australia, South America, Europe and
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