AUGUSTA, Maine (AP) A second case of highly pathogenic avian influenza has been discovered in Maine a few days after the first documented case.

The Maine Department of Agriculture, Conservation and Forestry said Wednesday that federal authorities found avian influenza in a sample taken from a small flock of non-commercial backyard birds in Knox County. The agency said the birds were not poultry.

Federal officials said Sunday that they had discovered the influenza for the first time in the state. It was found in another backyard flock in Knox County, they said.

Wild birds often spread the virus to domestic poultry.

The state agriculture department said the new case was located about two miles (three kilometers) from the first case. The agency said there is now a six-mile (10-kilometer) surveillance zone around both premises.

The state advised backyard and commercial operators to keep birds indoors to prevent the spread of the disease.