Four more cases brought the total to 60 Iowa sites contaminated with highly pathogenic avian influenza.
A Buena Vista turkey farm with about 24,000 birds, plus three Sioux County facilities with a total of about 250,000 birds, were added to the list of Iowa sites where testing has been positive for H5 avian influenza. The Sioux County sites included a commercial laying operation, a pullet farm and a backyard chicken flock.
Nearly 26 million birds were affected in Iowa as of Tuesday, May 19, 2015, according to the Iowa Department of Agriculture.
State officials said waterfowl such as ducks, geese, swans and gulls, as well as shorebirds like herons and egrets, carry the H5N2 virus. It is spread by direct contact with fecal droppings or respiratory secretions of infected birds, and can be spread by contaminated objects like shoes, clothing and equipment.
Affected flocks are quarantined; when the virus is confirmed, contaminated flocks are euthanized. Flocks within 10 kilometers of a confirmed bird flu site are also quarantined as a precaution.
There are no food safety concerns associated with bird flu, and there has never been a reported case of human or mammal infection.
The virus had not been previously found in North America, the Iowa Department of Agriculture site said.