Minnesota has lifted the last remaining quarantines on poultry farms that were infected with a deadly form of bird flu, officials announced Tuesday, marking a milestone in the state's recovery from an outbreak that cost its turkey and egg producers more than 9 million birds.

Ninety percent of the 108 infected farms were cleared to restock as of Oct. 6. The few remaining sites have now completed the cleaning, disinfection and testing needed to gain approval for restocking, the Board of Animal Health said in a statement.

Minnesota announced its first case of the highly pathogenic N5N2 March 5 and confirmed its last case June 5. Restocked poultry on all affected farms have tested negative, providing additional assurances that the virus has been eradicated from Minnesota, the board said.

While seeing no new cases is encouraging, detecting future cases remains a possibility, State Veterinarian Bill Hartmann said.

U.S. poultry producers, primarily in the upper Midwest, lost more than 48 million birds to , mostly in April and May. Minnesota, the country's top turkey producer, and Iowa, the top chicken-egg producer, were the hardest-hit states.

While no strains of highly are currently circulating in Minnesota's domestic flocks, the board said it remains vigilant in case the disease reappears.

The U.S. Department of Agriculture says wild birds, particularly ducks, appear to be the main reservoir for these viruses and could still be a threat to poultry this fall and winter. The agency has spearheaded extensive improvements in biosecurity practices to prevent and respond to any future cases.