Chickens sit in cages at a Changji farm, in China's western Xinjiang region

Health experts are urging the world not to be complacent about avian flu. The illness has had a small human death toll, but experts say it has the probability to become a worldwide pandemic. And, although the disease has largely affected domestic poultry in Asia, signs that it is spreading include its recent discovery in migratory birds in Russia and Kazakhstan.

During his 30-year career, public health official Michael Osterholm, has seen some grim developments, including the emergence of AIDS and antibiotic-resistant infections. These, though, he says, pale in comparison to a potential widespread outbreak of avian flu.

"Without a doubt, if you were to add up my entire public health career concerns, worries and in some cases, nightmares, if you added them all together, they collectively do not meet the concern, the worries and the nightmares that I have about the issue of a pending pandemic of influenza," he said.

Mr. Osterholm directs the University of Minnesota's Center for Infectious Disease Research and Policy and works for the Department of Homeland Security.

"It is not if it [avian flu] is going to happen," he said. "It is when, and where, and how bad."

He spoke in Washington at the Woodrow Wilson International Center for Scholars. He was joined by Canadian journalist Helen Branswell, a medical writer who has spent more than two years researching pandemic influenza and the avian flu strain that has been killing people and birds in recent years, H5N1.

"Welcome to my nightmare," she said.

Ms. Branswell said she feels no one, including the World Health Organization, is ready to deal adequately with an avian flu pandemic. She added that several key lessons should have been learned following Canada's recent experience with the deadly Severe Acute Respiratory Syndrome, or SARS.

"And the first is, in the modern world, infectious diseases travel at jet speed," she said. "Pandemic planners tell us we may have up to three months before a pandemic virus hits North America. I have no idea why they are so optimistic. SARS was raging in Toronto hospitals before it even had a name, before the WHO warned anybody to be on the lookout for the disease."

Agriculture Ministry officials take blood sample from an Australian pelican at Gembira Loka Zoo in Yogyakarta, Indonesia

The current H5N1 strain of avian flu first appeared in Hong Kong, in chickens, in 1997. Since then, tens of millions of birds around Asia have died or been killed to prevent them from becoming infected. Meantime, the virus has shown that it can jump from birds to humans, with a mounting death toll of about 60 people.

Public health official Michael Osterholm says he is alarmed because H5N1 is similar to the virus that caused a huge flu pandemic in 1918, in which as many as 100 million people died worldwide.

"In general terms, we are not much better able to handle acute respiratory distress syndrome, in any number of cases today, than we were in 1918," he said. "So, do not go back and say, well, it is different today, it is not 1918. Unfortunately, folks, it is 1918 all over again, even from a clinical response standpoint."

He said experts cannot say for certain what a future avian flu pandemic would look like, but he estimates a human death toll anywhere from 30 million to 384 million people.

Mr. Osterholm says he believes developing effective and economically feasible vaccines for birds and for humans is one way to help avert a worldwide crisis. He added that governments need to show they have the political willpower to deal with the avian flu outbreak he is certain will occur.

George W. Bush

One sign that attention at the highest levels is being paid to avian flu came in President Bush's remarks to the U.N. General Assembly.

"If left unchallenged, this virus could become the first pandemic of the 21st century," the president said. "We must not allow that to happen. Today I am announcing a new International Partnership on Avian and Pandemic Influenza. The Partnership requires countries that face an outbreak to immediately share information and provide samples to the World Health Organization. By requiring transparency, we can respond more rapidly to dangerous outbreaks and stop them on time."

The U.S. government plans to host a meeting of senior officials to discuss the issue in the next few weeks.