Officials of the World Health Organization say they fear the bird flu virus in Southeast Asia could become a worldwide pandemic (search) capable of killing anywhere from two to seven million people.

And they say it could sicken billions of others. They're concerned because the bird flu virus (search) shows it can infect across species and has resisted efforts to stamp it out.

The virus first spread among chickens but killed 32 people this year in Thailand and Vietnam. It has also appeared in domestic cats and tigers in Thailand.

Scientists say, "the extent of the current outbreak in poultry is historically unprecedented." They say the best way to combat the disease is to overhaul the way animals are raised for food.