Swine flu transmission to humans occurred months before outbreak

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A new analysis of the current swine-origin H1N1 influenza A virus suggests that transmission to humans occurred several months before recognition of the existing outbreak.

The work, published online in Nature, 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 paper was co-authored by Michael Worobey, associate professor of ecology and evolutionary biology at The University of Arizona.

The outbreak of swine-origin H1N1 influenza A currently stands at pandemic alert Phase 6 on the World Health Organization classification, and it is crucial that the public understands what it is up against. The researchers use evolutionary analysis to estimate the time scale of the origins and the early development of the epidemic. They believe that it was derived from several viruses circulating in swine, and that the initial transmission to humans occurred several months before recognition of the outbreak.

The team concludes that “despite widespread influenza surveillance in humans, the lack of systematic swine surveillance allowed for the undetected persistence and evolution of this potentially pandemic strain for many years.”

“Our analyses indicate that this virus circulated for more than a decade unnoticed in pigs, so clearly we need to do a better job monitoring that reservoir,” Worobey said. “And once it jumped to humans, it then spread for several months under the radar before it was first noticed, which is troubling.”

While the situation is bad, Worobey said, it could have been much worse if this strain of virus was more deadly. “We now have a tremendous opportunity to apply the lessons learned here and get out in front of future emerging influenza strains rather than reacting to them relatively late in the game,” Worobey said.

Source: University of Arizona, USA

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