"Contrary to the popular assumption that the new swine flu pandemic arose on factory farms in Mexico, federal agriculture officials now believe that it most likely emerged in pigs in Asia, but then traveled to North America in a human. But they emphasized that there was no way to prove their theory and only sketchy data underpinning it. There is no evidence that this new virus, which combines Eurasian and North American genes, has ever circulated in North American pigs, while there is tantalizing evidence that a closely related “sister virus” has circulated in Asia. American breeding pigs, possibly carrying North American swine flu, are frequently exported to Asia, where the flu could have combined with Asian strains. But because of disease quarantines that make it hard to import Asian pigs, experts said, it is unlikely that a pig brought the new strain back West." - Steven Perez from Bookmarklet