Iowa Governor Terry Branstad declared a state of emergency in his state on Friday to confront a spiraling bird flu outbreak.

Millions of birds across the country have been infected by the highly pathogenic H5 avian flu in the most recent outbreak, which could result in the biggest death toll in U.S. history according to Reuters.

“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.”

In Iowa, 21 sites have presumed or confirmed cases.

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Write to Noah Rayman at noah.rayman@time.com.