Dover, Del. ? Officials responded to a new discovery of bird flu Tuesday by ordering a quarantine of 80 farms and the slaughter of 72,000 more chickens. The swift action was aimed at averting more bans on U.S. exports.

The second case of disease was found in a commercial flock of roaster-type chickens in northern Sussex County, at least five miles away from the farm where the first flock tested positive last week.

The chickens at the second farm were killed Tuesday afternoon, said Delaware Secretary of Agriculture Michael Scuse.

Perdue Farms said it had destroyed the 72,000 chickens to prevent the spread of the disease. The company said the flock was believed to have been infected by a nearby flock of chickens that was raised for the New York City live markets.

The first flock found to be infected was raised for the New York City live markets, state officials have said.

All sales of live poultry in Delaware, all sales or auctions of farm equipment and all farmer and grower-related meetings have been canceled. About 80 farms within a six-mile radius of the two farms will be quarantined, state officials said.

“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, a USDA economist.

Barricades are placed across the entrance to Hobo Farms in Greenwood, Del. The farm is the second site in Delaware to be affected by the avian flu. The flu strain is different from the one that has spread to the human population in Asia, killing at least 19, and experts said there was no threat to human health.

If the avian influenza does not spread, the effect of the bans could be short-lived, said Richard Lobb, a spokesman for the National Chicken Council, 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. In previous poultry disease outbreaks, foreign officials have ended bans quickly after they were assured that their flocks would be safe from contagion if they resumed imports, he said.

Delaware state veterinarian Edwin Odor said each flock is tested for the flu before slaughter, and said the food supply is safe. Under the quarantine, chickens over 21 days old will be tested every 10 days during the quarantine, which is expected to last a month, Scuse said.