World Health Organization officials urged governments on Wednesday to act swiftly to control the spread of the bird flu (search), warning that the world is in grave danger of a deadly pandemic triggered by the virus.

The bird flu has killed 45 people in Asia over the past year, in cases largely traced to contact with sick birds, and experts have warned the H5N1 virus (search) could become far deadlier if it mutates into a form that can be easily transmitted among humans. A global pandemic could kill millions, they say.

"We at WHO believe that the world is now in the gravest possible danger of a pandemic," Dr. Shigeru Omi, the WHO's Western Pacific regional director, said Wednesday.

He said the world is "now overdue" for an influenza pandemic, since mass epidemics have occurred every 20-30 years. It has been nearly 40 years since the last one.

Speaking at the opening of a three-day bird flu conference in Ho Chi Minh City, Omi said it is critical that the international community better coordinate its fight against the virus.

In recent outbreaks, bird flu has become more deadly than the strain found in 1997 in Hong Kong, making the situation more urgent, he said.

The mortality rate among identified patients who contract the disease from chickens and ducks is about 72 percent, Dr. Julie L. Gerberding, head of the U.S. Centers for Disease Control and Prevention, said on Monday. She added that her agency was preparing for a possible pandemic next year.

"If the virus becomes highly contagious among humans, the health impact in terms of deaths and sickness will be enormous, and certainly much greater than SARS (search)," Omi said, referring to severe acute respiratory syndrome, which killed nearly 800 people in 2003.

"This is why we are urging all governments to work now on a pandemic preparedness plan — so that even in an emergency such as this they will be able to provide basic public services such as transport, sanitation and power," he said.

The disease, which devastated the region's poultry industry last year as it swept through nearly a dozen countries, has killed 32 Vietnamese, 12 Thais and one Cambodian over the past year.

Officials acknowledge that one of the biggest challenges in controlling avian flu is in altering traditional farming practices in Asia where animals live in close, often unsanitary quarters with people.

"There is an increasing risk of avian influenza spread that no poultry-keeping country can afford to ignore," said Dr. Samuel Jutzi, of the United Nation's Food and Agriculture Organization in the conference's opening address.

Jutzi, director of the FAO's animal health and production division, said the avian flu virus will persist in Asia for years and coordinated efforts need to focus on controlling it at its source — in animals.

"This means addressing the transmission of the virus where the disease occurs, in poultry, specifically free-range chickens and wetland dwelling ducks, and thus curbing the disease occurrence in the region before it spreads to other parts of the world," he said.

The challenge for many countries affected by the virus is the lack of effective diagnostic tools and surveillance systems needed for early warning and timely response, he said.

The regional conference held in southern Ho Chi Minh City near the Mekong Delta where the latest outbreaks emerged this year has brought together scientists and representatives from more than two dozen countries.

Bird flu's reemergence in Vietnam, where 12 people have died this year alone, has shown the virus is now endemic in parts of the region.

"The longer the virus is circulating in animals, including chickens and ducks, the greater the risk of human cases — and consequently, the higher the risk of a pandemic virus emerging through genetic changes in the virus," Omi said.

The virus has proven to be "very versatile and very resilient," and has even been found in animals such as tigers and cats that weren't believed to be susceptible to influenza, he added.