A new trick was used by the H1N1 swine flu virus to spread efficiently in people. This has made experts think if a pandemic can be caused by a virus.

In April 2009, the H1N1 swine flu virus was first identified in people. But research that followed stated that the virus was present for past one decade and in pigs the duration could be even longer.

Yoshihiro Kawaoka of the University of Wisconsin-Madison's School of Veterinary Medicine and the University of Tokyo, said, "This pandemic H1N1 (virus) has this mutation and is why it can replicate so well in humans. This gives us another marker to help predict the possibility of future flu pandemics."

Lysine and asparagines are the two amino acids needed by a virus on certain sites on itself before it can make way towards people.

But amino acids in those two locations were not found by the scientists.

It was found by Kawaoka and colleagues that the lysine amino acid was residing instead in a completely different position in an experiment with mice. The virus was however effective in getting to humans cells.