A strain of highly pathogenic avian influenza, commonly known as bird flu, has been detected in a flock of backyard birds in Penobscot County this month for the first time since it appeared in Maine almost four years ago.

The case of H5N1 was confirmed on Dec. 1, according to the Maine Department of Agriculture, Conservation and Forestry, which reports cases by county and does not specify towns. Federal disease tracking data show the new case affected 90 birds and is one of the few known cases in eastern or northern Maine. Two flocks were affected in Hancock County in 2023, following two in Washington County the year before.

It’s only the third known detection in a backyard flock in Maine this year; the first two, in Cumberland County, were confirmed in February and affected about 110 birds. Statewide, health officials have raised the current risk level to high in response this month as the wild birds that typically spread the disease are migrating.

That risk level reflects the likelihood of birds getting sick, not people, according to Jim Britt, spokesperson for the state agriculture department. Commercial flocks haven’t been affected. The disease has been detected in numerous wild birds around Maine this year, primarily in southern and coastal counties.

While people can get bird flu, this strain isn’t considered a big public health risk, the U.S. Centers for Disease Control and Prevention has said. Human cases have come from exposure to birds and dairy cattle, according to the CDC, but there are no confirmed U.S. cases of people spreading it to each other.

Highly pathogenic avian influenza is generally spread to poultry through the droppings of wild birds or exposure to them. It was first found in Maine in 2022, and has been detected in a handful of flocks annually after numerous cases that year.

Signs of infection in poultry include low energy and appetite, soft or misshapen eggs, swelling around the head, purple wattles, combs or legs, coughing and sneezing, nasal discharge or sudden death.

To limit risk to their flocks, poultry owners can protect them from contact with wild waterfowl by providing indoor shelter and covering outdoor areas. Sick and dying birds can be reported to the state online.