A new research has revealed the origins of swine flu after scientists discovered that the transmission of the H1N1 influenza A virus to humans occurred several months before recognition of the existing outbreak.
India has confirmed a total of 23 cases of swine flu in the country, with the World Health Organisation declaring the outbreak as a pandemic.
In the new research, an international team, led by Oxford University, used evolutionary analysis to estimate the timescale of the origins as well as the early development of the swine flu pandemic.
According to the scientists, the virus was actually derived from several viruses circulating in swine, and that the initial transmission to humans occurred several months before recognition of the outbreak.
Lead scientist Dr Oliver Pybus said: "Using computational methods, developed over the last ten years at Oxford, we were able to reconstruct the origins and timescale of this new pandemic.
"Our results show this strain has been circulating among pigs, possibly among multiple continents, for many years prior to its transmission to humans."
The research highlights the need for systematic surveillance of influenza in swine, and provides evidence that new genetic elements in swine can result in the emergence of viruses with pandemic potential in humans.
The scientists concluded that "despite widespread influenza surveillance in humans, the lack of systematic swine surveillance allowed for undetected persistence and evolution of this potentially pandemic strain for many years."
The team included scientists from Oxford University, the University of Edinburgh, the University of Hong Kong and the University of Arizona. Their findings are published in the latest edition of the 'Nature' journal.