"We estimate this could cost, in fact, certainly over 1 trillion dollars and perhaps as high as 2 trillion dollars, in the worst case scenario, so I think the threat, the economic threat, remains real and remains substantial," said Jim Adams, vice president for East Asia and the Pacific and head of the bank's avian flu task force.

Earlier estimates last year of about 800 billion dollars in economic costs were basically written on the back of an envelope, he said at a press conference during the International Monetary Fund and World Bank annual meetings in Singapore.

"But more recent financial modelling had revealed a sharper threat should the virus mutate and pass easily among people," he also said, adding a severe pandemic could cost more than 3 percent of the global economy's gross national product.

The World Bank has provided advice and financing totaling 150 million dollars to projects to tackle bird flu in Albania, Armenia, Azerbaijan, Georgia, the Kyrgyz Republic, Laos, Moldavia, Nigeria, Tajikistan, Turkey and Vietnam.

The international community has pledged to donate 2 billion dollars to developing countries, and of this, 1.2 billion dollars has been committed so far.

Asia has been hardest hit, with 127 out the 144 human deaths arising from bird flu since 2003 occurring in East Asian countries, other officials of the bank said.

/Xinhua/