Japan : Clue found to why swine flu spread in people

Via Reuters :

" The H1N1 swine flu virus underwent a mutation and used a new trick to spread efficiently in people, another signal to help experts predict whether a flu virus can cause a pandemic, researchers said on Friday.

The H1N1 swine flu virus was first identified in people in April 2009 but genetic research later suggested it had in fact been circulating for at least a decade and probably longer in pigs.

"This pandemic H1N1 (virus) has this mutation and is why it can replicate so well in humans," wrote Yoshihiro Kawaoka of the University of Wisconsin-Madison's School of Veterinary Medicine and the University of Tokyo, who co-authored the paper."