The fight against bird flu has improved around the world, but the situation remains critical in Egypt and Indonesia where the risk of the H5N1 virus mutating into a major human threat remains high, the UN health agency said Wednesday.
"In the 15 or so countries in Asia, Eastern Europe and the Middle East where the H5N1 virus was introduced during the past six months, it was rapidly detected and eliminated or controlled," said Joseph Domenech, head of veterinary services at the World Health Organization (WHO) in Rome.
"Most affected countries have been very open about new outbreaks," he said. "This shows that countries are taking the H5N1 threat seriously. They are better prepared today and have improved their response systems."
But, speaking to reporters at a WHO technical meeting on avian influenza, he warned that Indonesia was "where the risk is the higher of getting the virus at the origin of human pandemic, as it was in China, Vietnam and Thailand three years ago".
"Same conditions in Egypt," Domenech added. "There is a high density and a lot of contacts."
"The H5N1 virus is not stable and keeps constantly changing," Domenech warned.
"On one occasion in China last year a new virus strain appeared with different immunologic characteristics which made it necessary to modify the vaccines used in the region concerned.
"This emergence of a new strain may have happened again more recently in Indonesia."
Transmission of bird flu to humans remains very rare, and limited to those in frequent contact with infected poultry. But in WHO's view, a potential human pandemic cannot be ruled out so long as the virus lingers in birds.
Egypt and Indonesia remained high-risk because of the permanent contact that many people in both nations have with domesticated birds.
In Indonesia alone, WHO estimates that there are more than 13,000 poultry markets, where birds from many different places are exposed to each other, raising the danger of transmission.
The situation is also critical in Nigeria, even if only one human case has come to light there, because the west African nation borders on four or five countries where HIV has been traced back to animals.
Domenech thanked the "speed and transparency" with which some countries, such as Ghana or Togo, reacted to bird flu outbreaks, making it easy for international organisations to intervene and for vaccines to be distributed.
Since 2003, the H5N1 virus has infected 310 people, including 190 who went on to die, according to WHO figures. Some 250 million poultry have also been culled, or have died from bird flu.