A Michigan dairy worker has been diagnosed with bird flu — the second human case associated with an outbreak in U.S. dairy cows.

The worker had been in contact with cows presumed to be infected, experienced mild eye symptoms and has recovered, U.S. and Michigan health officials said in announcing the case Wednesday. A nasal swab from the person tested negative for the virus, but an eye swab tested positive, “indicating an eye infection,” the U.S. Centers for Disease Control and Prevention said in a statement.

The risk to the public remains low, but farmworkers exposed to infected animals are at higher risk, health officials said. They said those workers should be offered protective equipment, especially for their eyes.

The first case happened in late March, when a farmworker in Texas was diagnosed in what officials called the first known instance globally of a person catching this version of bird flu from a mammal. That patient also reported only eye inflammation and recovered.

Since 2020, a bird flu virus has been spreading among more animal species — including dogs, cats, skunks, bears and even seals and porpoises — in scores of countries. The detection in U.S. livestock earlier this year was an unexpected twist that sparked questions about food safety and whether it would start spreading among humans.

That hasn’t happened, although there’s been a steady increase of reported infections in cows. As of Wednesday, the virus had been confirmed in 51 dairy herds in nine states, according to the U.S. Agriculture Department. Fifteen of the herds were in Michigan.

Health officials in Michigan have declined to say how many people exposed to infected cattle have been tested or monitored. U.S. officials said they had tested 40 people since the first cow cases were discovered in late March.

The CDC’s Dr. Nirav Shah praised Michigan officials for actively monitoring farmworkers. He said health officials there have been sending daily text messages to workers exposed to infected cows asking about possible symptoms, and that the effort helped officials catch this infection. He said no other workers had reported symptoms.

USDA is expanding financial incentives to dairy farmers whose herds have not yet been infected with the virus, Eric Deeble. a federal agriculture official, said Wednesday.

The virus has been found in high levels in the raw milk of infected cows, but government officials say pasteurized products sold in grocery stores are safe because heat treatment has been confirmed to kill the virus.

The new case marks the third time a person in the United States has been diagnosed with what’s known as Type A H5N1 virus. In 2022, a prison inmate in a work program picked it up while killing infected birds at a poultry farm in Montrose County, Colorado. His only symptom was fatigue, and he recovered. That predated the virus’s appearance in cows.