May 26, 2011
PARIS (AFP) - Scientists in Hong Kong and Singapore said on Wednesday they had established the widest-ever picture of how the flu virus circulates in pigs, a work that should aid efforts to combat a future influenza pandemic.
Driven by cross-border trade, the range of porcine flu viruses turns out to be larger than thought, they reported in the science journal Nature.
The findings are important because pigs play a key role in the emergence of influenza pandemics in humans.
They are a major viral source in themselves but also can act as a kettle, breeding new flu strains from swine viruses and viruses from poultry and humans in close proximity.
Sometimes -- mercifully rarely -- a novel virus can be a killer.
Tens of millions of people died in flu pandemics in 1918, 1957 and 1968.
A pandemic that occurred in 2009 had about the same lethality as ordinary "seasonal" flu. It is commonly but erroneously called swine flu, for it is a combination of bird and human as well as pig viruses.
Vijaykrishna Dhanasekaran, a specialist in virus evolution at the Duke-National University of Singapore Graduate Medical School in Singapore, said the study showed clearly that viral diversity among pigs had grown.
"The repertoire of viruses that humans are in contact with every day has increased, and this may lead to a higher likelihood of swine-to-human transmission, although the risk remains unquantified," he said.
The research looked at the epidemiology, genetics and immune response to 650 viruses taken from slaughtered pigs in Hong Kong between 1998 and 2010.
These were compared with data on porcine flu viruses found in Europe, North America and elsewhere in Asia stretching back 34 years.
The picture shows the genetic ebb and flow of three major lineages of virus -- classical, Eurasian avian-like and triple reassortant -- and shows how specific sub-types surfaced in Hong Kong pigs, including combinations of all three groups.
Understanding these evolutionary dynamics should help pinpoint which flu viruses among pigs are best able to adapt to a human host, the authors hope.
