(Adds details, background)
CHICAGO, Oct 7 (Reuters) - A highly lethal form of avian flu infected a commercial flock of breeding chickens in Arkansas, the U.S. Department of Agriculture said on Friday, widening an outbreak of the disease in the key southern producing region.
Nationwide, more than 47 million birds have been killed by avian flu or culled to control its spread this year in the nation's worst outbreak since a record 50 million birds were wiped out in 2015.
Top states for raising broiler chickens for meat, such as Georgia and Alabama, had largely escaped infections in commercial flocks before the case in Arkansas.
Arkansas produced more than 1 billion broiler chickens last year, making it the third biggest producing state, U.S. government data show.
The disease hit a commercial broiler breeder chicken flock in Madison County, Arkansas, in the northwest corner of the state, the USDA said. State officials quarantined the premises, and birds there will be culled, the agency said.
Europe has experienced its worst bird flu crisis ever this year, with nearly 50 million poultry culled. The persistence of the virus over the summer has raised the risk of widespread infections next season, the EU's Food Safety Agency said. (Reporting by Tom Polansek; Editing by David Gregorio)