By Alex Kirby
BBC News Online environment correspondent
Bird flu could develop into a threat big enough to overturn world order if it evolves to transfer directly from person to person, a UK scientist says.
The avian flu virus continues to evolve
Dr John McCauley, of the Institute for Animal Health, said the virus could be 20 times worse than the 1918 pandemic.
That is estimated to have killed up to 40 million people, with later influenza outbreaks also killing millions more.
Dr McCauley said there was a realistic chance of the current avian flu virus evolving to threaten people directly.
Dr McCauley, whose research into avian influenza is being funded by the Biotechnology and Biological Sciences Research Council (BBSRC), was speaking to BBC News Online.
He said: "At the moment the virus affects humans only after transferring to them from poultry. In 1997, six people died in Hong Kong after 18 became infected. This year, 23 patients have died from a total of about 34 people infected in south-east Asia.
"That means there is a mortality rate from some strains of highly pathogenic avian influenza of between 30 and 60% of those infected." In 1918, the rate would have been about 1 or 2%.
"There's no reason to say the virus will not continue to evolve so that it can transmit directly from one person to another. There's a realistic chance that could happen.
AVIAN FLU ALERT
First jumped "species barrier" from bird to human in 1997
In humans, symptoms include fever, sore throat, and cough
Types which threaten humans are influenza A subtypes H5N1 and H9N2
"If it does - if the virus becomes adapted to man and can transmit efficiently - there'll be no point in selling a vaccine. You might as well give it away at that stage, because money would be meaningless. The world order would change."
Dr McCauley said the global flu epidemics of 1957 and 1968 had involved a mixing of avian and human forms of the virus, and it looked as if that had happened in 1918 as well.
So people killing infected birds should be taking anti-flu drugs to guard against the possibility of being infected with both forms and creating a pandemic.
Dr McCauley said: "Any complacency could lead to devastation for the UK poultry industry. I think the avian form of the disease has not been cleared up in any of the affected countries."
In poultry the effects of bird flu can range from a mild touch of disease to a highly fatal and rapidly spreading epidemic.
Teams from the Institute for Animal Health and the universities of Cambridge and Oxford are cooperating to unravel the dynamics of bird flu.
Cambridge scientists, with the Roslin Institute, are working to produce a breed of chicken that is genetically resistant to infection by the virus, engineering the bird's cells to produce small molecules of RNA that can selectively prevent its replication.
The BBSRC is to fund 14 new research projects costing £11m ($19.5m) under its Combating Viral Diseases of Livestock Initiative.