Swine Flu Existed In Pigs For More Than A Decade

Before swine flu began infecting humans, it existed among pigs for at least a decade, according to a report issued on Tuesday.

Michael Worobey of the University of Arizona told flu experts on Tuesday that better systems of monitoring diseases among pigs and humans was needed, and the spread of the H1N1 virus is exhibit A.

"This virus most likely has been circulating under the radar in pigs for the better part of 10 years," said Worobey.

"Once it jumped into humans it probably circulated for months under the radar. There is lots of room for improvement of our surveillance of swine flu in pigs."

Worobey presented his report before a meeting called for by the US Institute of Medicine in order to determine better ways to prepare for possible future pandemics.

Swine flu was first reported in humans in April and had become a pandemic by June.

"We could do more for surveillance in humans," Worobey said. "If we had been doing that kind of thing, we may have picked up on this new strain a month or two or three before we did."

Worobey used molecular tests to trace how the H1N1 virus made the transition from swine to humans.

He said influenza viruses mutate on a regular basis and are simple to trace.

He told the meeting that it is difficult to pinpoint exactly where humans first became infected with the virus, but once it occurred, the genes began to change quickly.

"They seemed to be evolving at something like 1.5 times the rate they evolved in swine,"

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