Are you worried about the bird flu yet?

International health authorities say the death on Wednesday of a young man in Thailand from bird flu provides another worrying sign that the world may be edging toward a long-awaited influenza pandemic against which humans have little protection.

Tests have confirmed that the death of the 18-year-old man was caused by the H5N1 bird-flu virus, the first such human casualty in Thailand since the disease re-emerged in Asia in July. The Associated Press reported that the man, who raised fighting cocks, was admitted to a hospital on Sept. 4, four days after falling ill.

The H5N1 avian-flu virus is now spreading rapidly in birds, partly helped by infected wild ducks that have carried it to new spots. The virus has now surfaced in nine countries, emerging most recently in Malaysia, and is mutating in ways that make it more infectious in mammals. Dutch researchers, for instance, found that cats could contract it.

So far, avian influenza has killed 28 people in Asia this year. The first outbreak in January devastated poultry stocks and led authorities to cull tens of millions of birds.

"We have never been as close to a pandemic as we are now," said Klaus Stohr, who heads the World Health Organization's influenza program, based in Geneva. Nancy Cox, head of the influenza branch at the U.S Centers for Disease Control and Prevention in Atlanta, says that, like the WHO, her organization is ramping up efforts to improve flu surveillance in Asia. "We believe the pandemic threat is greater now than it has been in decades," Ms. Cox said.

A flu pandemic would be far deadlier than the usual flu bug that causes millions of Americans and Europeans to call in sick each winter. Annual flu outbreaks occur when the structure of the virus undergoes small changes, enabling it to evade the immunity that people have acquired from vaccinations or previous infections. But sometimes a flu virus known as influenza A undergoes drastic changes -- and nobody is immune to it. If the bug also acquires the capacity to jump from one person to another, the chances of a pandemic become far greater. The Spanish flu pandemic of 1918, for example, killed at least 20 million people.

The H5N1 virus hasn't yet acquired the capacity to spread from person to person, but the latest developments in Asia have increased that risk, said Dr. Cox. The virus could mutate enough so that it adapts to human hosts. Or if H5N1 infects a person already suffering from a regular bout of influenza, it could combine with that virus and form a deadly hybrid. Because of jet travel and urban overcrowding, the virus could spread quickly, as happened with the Severe Acute Respiratory Syndrome virus.

Health authorities have long warned that the world isn't prepared for a flu pandemic. If a superflu breaks out, the race will be on to vaccinate people right away. But that could be difficult as vaccines take months to prepare. Earlier this year, laboratories affiliated with the WHO provided a prototype H5N1 vaccine to several pharmaceutical companies. So far, only two drug makers, Sanofi-Aventis SA of France and Chiron Corp. of Emeryville, Calif., have agreed to make clinical batches of the vaccine...