TORONTO -- A new analysis of the swine flu virus suggests the first cases in humans probably started several months before authorities recognized there was an outbreak.
The international team of authors say the work highlights the need for ongoing and sys-tematic surveillance of influenza in swine herds.
They used evolutionary analysis to estimate the time scale of the origins of the genes in the new virus, a never-before-seen H1N1 influenza A virus.
The work, which is published in the journal Nature, suggests the virus may have come to-gether years before it jumped into humans.
The authors say their findings also do not support an earlier hypothesis that the virus might have been engineered in a laboratory and released by mistake.
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The World Health Organization is believed to be on the verge of declaring swine flu a pan-demic.
