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This 2005 electron microscope image shows an avian influenza A H5N1 virion. On Wednesday, May 22, 2024, Michigan health officials said a farmworker has been diagnosed with bird flu, the second human case connected to an outbreak in U.S. dairy cows.Cynthia Goldsmith/The Associated Press

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

The patient had mild symptoms, Michigan health officials said in announcing the case Wednesday. The person had been in contact with cows presumed to be infected, and the risk to the public remains low, officials said.

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 reported eye inflammation and was treated with an antiviral drug.

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 there have declined to say how many people exposed to infected cattle have been tested or monitored.

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.

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