A highly pathogenic form of avian influenza was reported in a commercial turkey flock in Iowa, making it the second reported outbreak in the top egg-producing state of the United States in less than a week, reported Reuters.

The outbreak was confirmed in Buena Vista County on Monday by the Iowa Department of Agriculture and the United States Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS).

"The Iowa Department of Agriculture and USDA APHIS are working diligently with producers to trace back, control and eradicate this disease from our state," Iowa Secretary of Agriculture Mike Naig said in a statement.

Governor Kim Reynolds also signed a disaster proclamation for Buena Vista County to assist with tracking, detection and elimination of the disease.

Last week, Iowa reported a case of avian influenza in a backyard poultry flock in Pottawattamie County. Over the past month, highly lethal avian influenza cases have been confirmed at commercial farms in Indiana, Kentucky and Delaware, triggering export restrictions for US poultry products.

In 2015, Iowa was at the centre of the biggest-ever US outbreak of avian flu, which killed about 50 million birds.