EDINBURGH, Scotland, June 11 (UPI) -- U.S., Chinese and British researchers say the H1N1 swine flu virus was transmitted to humans long before the existing outbreak was noticed.
The scientists said their analysis of the current swine-origin H1N1 influenza outbreak -- declared a pandemic Thursday by the World Health Organization -- calls for the need of 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.
Andrew Rambaut of the Institute of Evolutionary Biology at the University of Edinburgh in Scotland and colleagues estimated the timescale of the development of the epidemic. They determined it was derived from several swine viruses and the initial transmission to humans occurred several months before recognition of the outbreak.
"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," the researchers said.
The study that included scientists from the University of Hong Kong, the University of Arizona in the United States and Oxford University in Britain appears in the early online edition of the journal Nature.