Since then, it's infected more than 100 people there, at least 60 of whom have died.
This more virulent strain -- known as H5N1 -- can't yet pass among humans. But health officials are increasingly warning that the virus could evolve into one that can. And if that happens, they say, a pandemic that kills millions of people might be the result.
Now, bird flu has spread. This week it reached the edge of Europe, with the H5N1 strain being found in Turkey and -- possibly -- Romania. And the warnings are getting louder.
U.S. Health Secretary Mike Leavitt spoke today during a visit to Vietnam.
"We have a need for action now, but it is a preparation. We are preparing for what is a possibility," Leavitt said. "What is the probability that [an avian-flu pandemic] will occur? No one knows, but signs that have occurred in Turkey and Romania and other countries along the natural [bird migratory] flyways are certainly troubling signs."
Troubling signs, indeed, but the global response is growing.
The aim is first to stop the virus from spreading to farms, where there is a greater chance it could infect humans.
Millions of birds have already been slaughtered in Asia, and now, too, in Turkey and Romania.
Russia culled thousands of birds and put a quarantine on affected areas after an outbreak in Siberia this summer.
European veterinary experts were to hold talks today in Brussels. European Union foreign ministers will meet on 18 October to discuss emergency measures.
The bloc has already banned imports of live birds from Turkey and Romania, and is considering telling farmers in risk areas to feed poultry indoors -- as South Korea has already done. The idea is that this would keep domestic poultry out of contact with wild, migratory birds that might carry the disease.
And in Greece, hunters have joined the fight, agreeing to hand over bird carcasses for inspection. Nikos Papadodimas is president of the Greek Hunters' Association.
"We will give, and have already sent, 1,000 specific breeds of birds from all over the country," Papadodimas said. "Tests of these will scientifically show if there is an existence of the problem. This can't happen any other way, because only hunters have contact with these birds. How can anyone else find them?"
Countries are taking other measures in case more people do get sick -- or, worse, the virus mutates and triggers a pandemic.
The United States is considering options such as using the military to enforce a quarantine if necessary.
The World Health Organization has urged countries to stockpile medicines like Tamiflu that can work against bird flu in humans. It's also urging countries to develop "preparedness plans" in case of a pandemic triggered by avian flu -- at least 40 have done this so far.
But the problem is, the countries most at risk are often the least prepared. Professor Ian Jones is a virology expert at Reading University in the United Kingdom.
"The problem is that the current policies vary across the world," Jones said. "And so what you have is a sporadic response to the threat and not a unified response, particularly in countries that can least afford to put those measures in place and yet where there is a significant danger that the virus can break out."
Meanwhile, drug companies are also racing to develop a bird flu vaccine.
But experts warn an effective one may be months or even years away. And there are worries that it might be difficult to make enough.
That's led some to question whether the money spent on vaccine research would be better spent on preventive measures.
Alejandro Thiermann, president of the International Animal Health Code, an intergovernmental group that helps control animal diseases, said that "investment has to be made in improving this infrastructure which is going to leave us in a better position for the next pandemic. This is not going to be the last one."
'Most Aggressive' Strain Of Avian Influenza Discovered In Turkey, Possibly Romania