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Swine Flu resided in Pigs for a decade

The pandemic H1N1 influenza was circulating undetected in pigs for at least a decade before it migrated to people, and better surveillance is needed among both pigs and people.

Molecular tests show the swine flu virus made a mutational jump as it passed from pigs to humans, Michael Worobey of the University of Arizona told a meeting of flu experts.

H1N1 was first detected in April this year and declared a pandemic in June. It quickly spread around the world but so far causes moderate illness.

The Institute, an independent organization that advises the U.S. government and other bodies on health matters, called the meeting to examine the pandemic and look for ways to better prepare for the next one. Influenza viruses mutate regularly and are easy to trace using their rate of change, said Worobey. He collaborated with researchers around the world who dug out samples from over a decade. By comparing recent gene sequences to older samples, Worobey was able to track the evolution of the pandemic.

Although it is hard to determine where people first became infected, because doctors rarely test patients for influenza and even more rarely are the viruses genetically sequenced.

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