Thousands of chickens have been slaughtered in the United States amid fears that the U.S. version of avian flu could destroy the multi-billion dollar-a-year U.S. poultry industry. Unlike the virus that's swept through Asia, U.S. officials are not concerned that the U.S. version could infect humans. But Asian countries are worried about the importation of the U.S. bird flu.

The American version of the avian flu that's infected flocks in Delaware, known as H-7, has never been known to jump the species barrier from poultry to humans. But it's extremely contagious and deadly among chickens. Since the virus was detected last week, almost 100,000 chickens at two sites in Delaware have been slaughtered.

Poultry farmers in neighboring states are taking precautions to prevent H-7 from spreading, including quarantining chickens suspected of being sick and sending them to labs for testing.

The safety measures also include careful monitoring of the transport of chickens from one high risk state to another, according to poultry scientist Gregory Martin at Penn State University, in University Park in Pennsylvania.

"We're tracking trucks and equipment and supplies through these areas. So, we try to do the best job we can to avoid contact with anything that might have the virus," he said.

U.S. drug makers are also working to develop a vaccine to inoculate healthy chickens against the virulent H-7. But Professor Martin says Asian countries, not wanting to risk their own flocks, are not receptive to resuming imports of chickens from the United States. "Not yet that I can tell," he said.

China has joined a growing list of Asian countries, including Japan, Malaysia and South Korea, that has banned the importation of U.S. chickens. China and other countries worry that importation of H-7-infected poultry from the United States could wipe out their own flocks.