A Stearns County dairy herd has tested positive for the bird flu: What you should know

Minnesota officials have quarantined a Stearns County dairy herd after milk samples tested positive for the H5N1 strain of bird flu.

The U.S. Department of Agriculture confirmed the results March 21, according to a news release from the Minnesota Board of Animal Health. It's the first case of bird flu detected this year in a dairy herd in Minnesota, the St. Paul Pioneer-Press reported.

The herd will be quarantined until tests indicate it is no longer infected, the news release says. The public milk supply isn't at risk, as all milk sold in stores is pasteurized to kill viruses and bacteria.

There have been confirmed cases of bird flu in at least 989 dairy herds in 17 states, according to the Centers for Disease Control and Prevention. 

Here's what else to know about bird flu and how the state monitors its dairy herds.

What is bird flu?

Bird flu is a virus that spreads among wild birds but can also infect poultry and livestock. The ongoing outbreak has caused a widespread egg shortage in recent months as infected chickens are killed to stop the spread of the disease.

In humans, symptoms of bird flu can resemble a typical flu – fever, sore throat, muscle aches, nausea and congestion, among others – but can also progress into more serious respiratory symptoms, according to the Cleveland Clinic. In early January, a person hospitalized with bird flu in Louisiana became the first person in the U.S. to die of the disease, USA TODAY reported.

How is Minnesota monitoring its dairy herds for bird flu?

The Minnesota Department of Agriculture conducts tests of "pre-pasteurized, or raw, cow milk" collected from each of the state's roughly 1,600 dairy farms every month.

"Identifying which dairy herds are infected is important so we can prevent disease spread and protect both animal and human health," said Thom Petersen, the department's commissioner. "Regular sampling and testing will allow the MDA and partners to identify where the virus is present, monitor trends, and prevent spread of the virus in order to protect unaffected dairy herds and poultry flocks."

The Minnesota Department of Health, meanwhile, monitors the health of people who have had direct contact with infected animals or their environment.

What happens to dairy cows infected with bird flu?

The most common symptoms in dairy cows include low appetite, reduced milk production and thickened or discolored milk, according to the American Veterinary Medicine Association. 

While the virus is often deadly for birds, that isn't necessarily the case for cattle. Most dairy cows recover with "supportive treatment," and the average mortality rate has been about 2% or lower, the association says.

Still, dairy industry experts say the virus can reduce a herd's milk production by about 20%, according to a KFF Health News report.

Does bird flu spread from dairy cows to humans?

In April 2024, the CDC confirmed a person was infected with bird flu after being exposed to dairy cows in Texas that were also presumed to be infected, thought to be the first instance of "likely mammal to human spread" of the virus.

Of the 70 human cases of bird flu reported in the U.S., 41 were exposed by dairy herds, while another 24 were linked to poultry farms, though most have had a mild form of the disease.

The people most at risk of infection include farmers and other workers exposed to infected animals or animal products, along with animal care workers, such as veterinarians. The risk to the general public remains low, the CDC says.