British scientists have found a small mutation in the H5N1 strain of bird flu virus isolated from a Turkish child who died of it, the WHO said on Thursday, but medical experts said it was too soon to gauge its significance.
Only two samples from Turkey have so far been analysed at the World Influenza Centre of the National Institute for Medical Research in London. A further 15 or more are on their way from Ankara.
Victims of the deadly H5N1 strain have caught the virus from birds. But if it mutates into a form that can be easily transmissible between humans WHO officials fear a pandemic that could kill millions of people.
Michael Purdue, who is overseeing the response to the avian flu outbreak in Turkey on behalf of the WHO, said the mutation now being reported had been spotted before in East Asia -- where the disease has killed more than 70 people -- in Hong Kong in 2003 and Vietnam in 2005. It was too soon to say what it meant.
In a joint statement last night, the WHO and Sir John Skehel, director of the London institute, said: "Research has indicated that the Hong Kong 2003 viruses preferred to bind to human cell receptors more than to avian receptors, and it is expected that the Turkish virus will also have this characteristic."
The virus also bore similarities to samples isolated at a migratory point for birds in Qinghai, western China.
The mutation was in a surface protein, haemagglutinin, which the virus uses to attach to the respiratory tract. Purdue said it was "clearly not a constant change" since it had been seen only twice so far. He said the virus was still evolving.
Avian flu in birds has now been confirmed in 11 out of Turkey's 81 provinces, but with suspected cases in 14 other provinces. The disease appears to have spread remarkably rapidly from the rugged south-east to the Aegean coast.