A World Health Organization official says nations hit by bird flu must do more to quickly report and share information on the disease, if a pandemic is to be prevented.

WHO Western Pacific Director, Dr. Shigeru Omi, offered a mixed picture of moves to prevent a worldwide outbreak of bird flu. On the positive side, he says international efforts to fight the disease have increased in the past few weeks as wealthy nations joined the struggle.

In electron micrograph, bird influenza virus strain H5N1, seen in gold, grown in MDCK cells, seen in green (1997 CDC photograph)

On the down side, he says authorities have been losing more battles than they are winning in the fight against the H5N1 virus, and that all attempts to bring it under control in Southeast Asia have failed.

Dr. Omi called on affected nations to do more to quickly report on the disease, though he did not name any countries.

"I would like once again to urgently call on these countries to share with the international community the samples they are collecting from infected poultry and the people," he said. "Without those samples we cannot know if the virus is mutating, and we don't know if the virus is any closer to tipping the world into the unknown."

Dr. Omi says it is difficult to develop defenses against the H5N1 virus because it changes so quickly, and that is why timely information is vital.

Veterinary worker fixes his protective goggles before culling domestic birds on suspicion of bird flu in Ceamurlia de Jos, Romania

Since 2003, there have been more 60 human deaths from the H5N1 strain of bird flu in Southeast Asia, and tens of millions of birds have been killed because of the disease. Authorities say the virus is endemic among bird populations in the region.

So far most of the human victims contracted the virus from infected poultry. Authorities fear that the H5N1 virus could mutate into a form that passes easily from person-to-person, prompting a worldwide outbreak.

U.S. Secretary of Health and Human Services Michael Leavitt has been visiting Southeast Asian capitals this week to urge close cooperation controlling bird flu. The United States has pledged $25 million to improve global bird flu control efforts.