Iowa Governor Terry Branstad declared a state of emergency on Friday to help battle the toll that the recent bird flu epidemic is taking on the state's poultry industry.

"While the avian influenza outbreak does not pose a risk to humans, we are taking the matter very seriously and believe declaring a state of emergency is the best way to make all resources available," Branstad said in a statement. "We'll continue our work - as we've been doing since the first outbreak in Buena Vista County - in hopes of stopping the virus' aggressive spread throughout Iowa."

Thus far 21 different sites spanning 10 different counties in Iowa have cases that are either presumed or confirmed to be avian influenza.  The counties include: Buena Vista, Cherokee, Clay, Kossuth, Madison, O'Brien, Osceola, Pocahontas, Sac and Sioux.

The Iowa Agriculture Department announced the discovery of four more cases of the bird flue at a chicken farm with approximately 1 million birds in Madison County and three turkey farms in Sac, Pocohontas and Cherokee counties.

One the bird flu has been confirmed at a site, all of the birds must be destroyed to prevent the spread of the disease because it is so infectious.  Nationally, chicken farmers are having to kill approximately 21 million turkeys and chickens all because of the bird flu.

"This disease is having a far reaching impact and, unfortunately, it has continued to spread," Iowa Secretary of Agriculture Bill Northey said.

The disaster proclamation is effective immediately and will continue until May 31, unless it is either extended or terminated by the governor. 

The disaster declaration will allow the activation of the response and recovery portions of the Iowa Homeland Security and Emergency Management Department's Iowa Emergency Response Plan and will allow for the authorization of the deployment of state resources, supplies, equipment and materials necessary to monitor and fight the virus.

Iowa is the top egg producing state in the United States and is the third state to declare a state of emergency because of this latest viral outbreak.  Minnesota and Wisconsin declared states of emergency in April. 

"While the avian influenza outbreak does not pose a risk to humans, we are taking the matter very seriously," Branstad said in a statement.

So far, it is estimated that 16 million egg-laying chickens in Iowa are infected or are presumed to be infected with the virus, meaning that at least one-quarter of the state's flock will have to be killed and disposed of, state officials said.