Research blogging from Not Exactly Rocket science:
In the time since the words “swine flu” first dominated the headlines, a group of scientists from three continents have been working to understand the origins of the new virus and to chart its evolutionary course. Today, they have published their timely results just as the World Health Organisation finally moved to phase six in its six-tier system, confirming what most of us already suspected – the world is facing the first global flu pandemic of the 21st century.The team, led by Gavin Smith at the University of Hong Kong, compared over 800 viral genomes representing a broad spectrum of influenza A diversity. The viral menagerie included two samples of the current pandemic strain (the virus formerly known as swine flu and now referred to as swine-origin influenza virus (S-OIV)). Also in the mix were 15 newly sequenced swine strains from Hong Kong, 100 older swine strains, 411 from birds and 285 from humans.
The team used these genomes to build a viral family tree that shows the relationships between the strains and dates their origins. They found that S-OIV was borne of several viruses that circulate in pigs, with contributions from avian and human strains. The virus made the leap to humans several months before we twigged to its presence. It was spreading right under our noses, undetected because of our lack of surveillance of flu viruses in pigs.