A World Health Organization team is heading to Vietnam to help officials there contain the bird flu, which has devastated the country's chicken farms. The virus has killed at least three people in Hanoi and infected chickens in at least three places in Asia.

The United Nations health agency said Friday its team of experts will help Vietnamese officials contain the bird flu, which is spreading rapidly on Vietnamese chicken farms.

The World Health Organization says Vietnamese officials informed them Friday that the disease had hit at least 25 provinces. Mass slaughters of chicken are under way in several provinces.

But one WHO official says those culling the chickens could be in danger of catching the bird flu. The virus has killed at least three people in Vietnam recently.

Peter Cordingly is the WHO's regional spokesman.

"We're a little bit worried about the culling because we're not supervising it," he said. "When this culling goes on it's to be feared that there's quite a lot of virus in the air. But we are sending in protective equipment for the cullers - things like gloves, masks coveralls, goggles, head covers."

The chicken flu, or H5N1 virus, was identified when it jumped from chickens to infect humans in 1997 in Hong Kong. Six of the 18 people infected then died. The government contained the disease by slaughtering all chickens in the territory.

The WHO says the virus, which has in recent weeks re-emerged to infect chickens in Taiwan, South Korea, and Japan, has not yet learned to spread from human to human. But people working close to live poultry are at risk because the virus is found the bird's waste.

Microbiologist K.Y. Yeun of Hong Kong University says farmed birds are particularly prone to the disease. "Once there is a single bird that is infected, very soon the whole flock will be infected," he said. "And many times when you are selling and buying at the same time, you have new flocks coming in and mixing with the old flocks and the virus becomes amplified."

He says farms can prevent outbreaks by vaccinating poultry against all H5 viruses. Nets can help keep out migratory birds, which carry the viruses.

Many Asian nations are banning chicken imports from countries where the flu virus has been found. That could mean shortages as the region prepares for the important Lunar New Year, when families get together for traditional meals, often featuring chicken.