The same mutation was observed in virus samples from victims of the 2003 Hong Kong and 2005 Vietnam bird flu outbreaks. Experts stress that the known mutation is not in itself a reason for increased concern.
"This same mutation was identified in 2003 in Hong Kong and yet did not take off in a way that led to greater transmissibility either from chicken to human or human to human," Anthony Fauci, head of the U.S. National Institute for Allergy and Infectious Diseases, told the Reuters news service.
"It is unclear whether the mutation occurred in the person or whether it occurred in the chicken," Fauci added.
Genetic tests reveal that the Turkish flu victims almost certainly acquired the virus from sick birds, rather than from other humans.
NIMR researchers also report that the viruses found in Turkish victims are likely responsive to several antiviral drugs, including Tamiflu, which may help slow the spread of any potential pandemic.
New Tool
Earlier this week researchers from the Scripps Research Institute in La Jolla, California, unveiled a new tool that might help track any outbreak of pandemic bird flu in real time.
The technology, called a glycan array, is a grid of sugars similar to those found on the outsides of human cells.
Avian and human viruses recognize and attach themselves to different sugar structures.
Scientists using the array can identify genetic mutations that help avian flu virus strains bind more easily to human cells.
Researchers examined samples of the deadly 1918 "Spanish flu" virus and other pandemic strains, looking at specific amino acid mutations that could dramatically increase the ability of an avian virus to attach to human cells.
"It would appear that two mutations could change the specificity dramatically going from avian to human," said Scripps researcher Ian Wilson.
The array could track the appearance of any such mutations. They would likely occur, as they did during influenza pandemics in 1957 and 1968, when a primarily human virus acquired a few avian virus proteins.
"This array is basically ready for use to evaluate strains as they [adapt] from birds to humans," said James Paulson, director of the Consortium for Functional Glycomics at Scripps.
"It wasn't possible before to compare many different structures in such a way to assess very rapidly when this key mutation has occurred."
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