After having already detected the virus in wild birds on several occasions on the east coast in recent weeks, the department said on Feb 9 it had found the disease in birds on a farm in Indiana.

Yesterday it reported that two more farms had been affected, in Kentucky and Virginia.

The authorities have placed the sites in quarantine and the birds will be slaughtered to avoid possible spread throughout the country, which according to the USDA is the largest producer of poultry in the world.

No cases have been detected in humans so far and the disease does not present an immediate public health threat, authorities said.

But the agricultural sector will remain vigilant to avoid a repeat of the 2015 avian flu outbreak, which affected 211 farms in 15 states, from California to Indiana.

During that flare-up, nearly 50 million birds were killed and their carcasses destroyed, and several countries suspended US imports.

The department put total losses at about US$3.3 billion.

After the first case was discovered in Indiana last week, Mexico and China moved quickly to limit imports from that state.

A spokesman for the National Chicken Council said in an email to AFP that any detection of the virus was “worrying” but said the control and monitoring programme put in place by the authorities is “the most robust in the world”.

Tyson Foods, one of the largest chicken producers in the US, said when it released its results on Feb 7 that it had already increased preventative measures, in particular on the east coast of the US.

The group has limited the number of visits to its farms and increased cleaning time for vehicles travelling to them.

Europe is already experiencing an avian flu outbreak, with more than 18 million birds slaughtered in Italy and around 3 million in France since the first cases detected in farms at the end of November.