Pictured is an egg-producing chicken farm in Iowa, another state that has been hit by the virus, April 23, 2015. Reuters/Joe Ahlquist

The recent bird flu outbreak has hit its largest flock of the Midwest yet, striking a farm in Minnesota with 1.1 million hens, state officials said. It’s the eighth farm in the state to be hit by the H5N2 strain of the flu, which has also affected flocks in Iowa and Wisconsin.

Officials have struggled to contain the outbreak, which began spreading in March but dates to December. More than 5 million birds -- about 1.5 million of them chickens -- have been affected in Minnesota, where 8 percent of the annual turkey production so far has been lost because of the virus. Another 1.8 million birds in Wisconsin have been struck by the flu, and 18 million birds, the majority of them egg-laying hens, have been hit in Iowa, the Minneapolis Star Tribune reported.

The virus, which can kill a bird in 48 hours, has forced farmers with infected flocks to kill millions of birds in order to prevent the disease from spreading to other flocks and farms. Migratory wild birds such as geese and ducks have also been blamed for helping to transmit the virus through their droppings.

Even as officials express optimism that the outbreak will cease as the weather warms, both Minnesota and Iowa have declared states of emergency. Minnesota also rolled out its National Guard to help deliver large quantities of water used in the process of euthanizing large flocks of birds, and legislators in the state have proposed new legislation to increase funding to help farmers combat the bird flu.

Concerns about bird flu have also reached Washington, where members of Congress have begun to meet with farmers and local officials to discuss how to respond to the spreading virus. In late April, U.S. Sen. Amy Klobuchar, D-Minn., said she had pushed for more federal funding to compensate farmers for birds they are forced to euthanize, as well as for more research into how the disease was spreading and how it might be stopped.

Health officials have said that the bird flu poses no threat to human health and that adequately cooked chicken, turkey and eggs are safe for people to eat.