Officials took swift action after the second case of bird flu (search) was found in Delaware, ordering the slaughter of 72,000 more chickens and the quarantine of 80 farms as they tried to avert more foreign bans on a billion-dollar export industry.

The chickens were from a commercial flock in northern Sussex County and were killed Tuesday afternoon, said Delaware Secretary of Agriculture Michael Scuse.

Perdue Farms said it destroyed the chickens to prevent the spread of the disease and the flock was believed to have been infected by nearby chickens raised for the New York City live markets.

The disease was first found on a farm in Delaware's southern Kent County operated by an independent grower. State officials immediately ordered the slaughter of 12,000 birds.

About 80 farms in a six-mile radius of the two farms will be quarantined for at least 30 days, state officials said. Scuse said chickens over 21 days old will be tested every 10 days during the quarantine.

"This now is a very, very serious matter. We have a multibillion dollar industry at stake," Scuse said.

Seven nations, including some of America's largest export customers, have banned at least some poultry imports from the United States because of the bird flu cases.

Annual poultry exports total more than $1.7 billion, about $1.4 billion of it in shipments of broiler chicken. Countries that have banned U.S. imports, including China and Japan, imported at least $245 million in U.S. broiler chicken in the past 11 months, said David Harvey, an Agriculture Department economist.

If the avian influenza does not spread, the impact of the bans could be short-lived, said Richard Lobb, a spokesman for the National Chicken Council (search), a producers and processors trade group.

But U.S. officials must show the world that they have the disease properly diagnosed and are eradicating it, Lobb said.

No recalls have been ordered, agriculture officials said. The sale or the movement of chickens by large poultry companies has not been stopped, Scuse said.

Delaware officials have said the outbreaks are not related to the virulent variety of avian influenza that is blamed for the deaths of at least 19 people in Vietnam and Thailand. The Asian bird flu also forced the slaughter of an estimated 50 million birds as authorities in the stricken countries worked to rein in the spread of the contagious disease.