DES MOINES, Iowa (AP) – Another commercial egg farm in Iowa has been infected with bird flu, the first commercial farm case identified since April, when a turkey farm was infected, according to state agriculture officials.

The latest case is in Wright County in north central Iowa, about 80 miles north of Des Moines. The operation houses about 1.1 million chickens.

Iowa has had 15 commercial farms infected this year, including turkeys, egg-laying hens and other chickens. In addition, five backyard flocks have been infected. Because the virus is highly contagious, all birds on an infected farm are killed and disposed of to avoid the spread of the disease.

Iowa has been hardest hit with bird losses at more than 13.3 million this year before the latest farm was found infected.

Nationally more than 47.7 million birds have been affected in 43 states, including 251 commercial flocks and 328 backyard flocks, USDA figures show.

Most of the Iowa cases were during the spring migration of wild birds in March and April, with one reported in early May. The virus hadn’t been detected again until a backyard flock was infected on Oct. 20.

Federal and state agriculture officials had been concerned that the virus could return with the fall migration of wild birds, which often carry the virus but aren’t sickened by it. The virus can spread through droppings or the nasal discharge of an infected bird, which can contaminate dust and soil.

“We have been preparing for the possibility of additional outbreaks and are working closely with USDA and producers to eradicate this disease from our state,” said Iowa Secretary of Agriculture Mike Naig. “With migration ongoing, we continue to emphasize the need for strict biosecurity on poultry farms and around backyard flocks to help prevent and limit the spread of this destructive virus.”