U.S. Agriculture Secretary Tom Vilsack said he doesn’t expect major export losses for U.S. poultry producers from a bird flu outbreak that has spread to 24 states.

While the outbreak has prompted more than 80 countries to curb imported U.S. products, Vilsack said the restrictions have been limited to poultry raised in affected counties or states.

“There has not been an effort to do a nationwide restriction,” he said in a conference call with reporters. “We haven’t seen that, which is a positive indication.”

Improvements in biosecurity since a major outbreak in 2014 and 2015 have helped limit the spread, according to Vilsack. Also since then, international agencies have encouraged more targeted restrictions to combat animal diseases.

More than 50 million chickens and turkeys died from the disease or were depopulated during the outbreak that spanned 2014 and 2015, which cost the U.S. economy about $3.3 billion in losses, according to a USDA assessment. Eighteen countries at that time—including China, Russia, and South Korea—banned U.S. poultry.