The outbreak of bird flu that has stricken Minnesota turkey farms continues to grow.

Now in Iowa, 9.6 million egg-laying hens have been sickened, which equals nearly 20 percent of the total population of egg-laying hens in the state. Iowa is the top egg-producing state in the country.

Wisconsin and Minnesota have both declared states of emergency and authorized the National Guard to help control the spread of the H5N2 virus. It can kill a flock of chickens within 48 hours.

Farm workers have been taking extra precautions during the outbreak. H5N2 is a low threat to humans, but flu strains can mutate quickly. Even if humans were to become infected, officials say this particular strain isn't likely to pass from human to human due to its genetic makeup.

Researchers are still unsure how the disease is entering poultry facilities.

Read More:

• FERN's Ag Insider by Chuck Abbott (Food & Environment Reporting Network)
• New bird flu cases add 6 million birds in Iowa (The Des Moines Register)
• Increased human protections offered as H5N2 outbreak spreads (Reuters)