On May 30, the Centers for Disease Control and Prevention reported that a Michigan dairy worker tested positive for H5N1 bird flu. It was the fourth person to test positive for H5N1 in the United States, following another recent case in Michigan, an April case in Texas, and an initial case in Colorado in 2022. 

H5N1 bird flu has been spreading among bird species in the U.S. since 2021, killing millions of wild birds and poultry. In late March 2024, H5N1 bird flu was found in cows for the first time, causing an outbreak in dairy cows across several states. 

U.S. public health officials and researchers are particularly concerned about this outbreak because the virus has infected cows and other mammals and has spread from a cow to a human for the first time. 

This bird flu strain has shown to not only make wild mammals, including marine mammals and bears, very sick but to also cause high rates of death among species, says Jane Sykes, professor of small animal medicine at the University of California, Davis, School of Veterinary Medicine. 

“And now that it has been found in cattle, [it] raises particular concern for spread to all the animal species, including people,” adds Sykes.

Even though the risk for human infection is low and there has never been human-to-human transmission of H5N1, there are several actions you can take to stay protected. Read on to learn more about H5N1 bird flu and the current outbreak. 

What is H5N1? 

H5N1 is a type of influenza virus that most commonly affects birds, causing them severe respiratory illness and death. 

The H5N1 strain first emerged in China in the 1990s, and it has continued to spread around the world since then. In 1997, the virus spread from animals to humans in Hong Kong for the first time, infecting 18 people, six of whom died. 

Since 2020, the H5N1 strain has caused “an unprecedented number of deaths in wild birds and poultry in many countries,” according to the World Health Organization. 

Even though bird flu is rare in humans, an H5N1 infection can cause mild to severe illness and can be fatal in some cases. It can cause eye infection, upper respiratory symptoms, and pneumonia. 

What do we know about the 2024 human cases of H5N1 in the U.S.?

The Michigan worker who tested positive for H5N1 in late May is a dairy worker who was exposed to infected livestock. They were the first to experience respiratory symptoms—including a cough without a fever—during the current outbreak. They were given an antiviral and the CDC says their symptoms are resolving.

The Michigan farm worker who tested positive earlier in May only experienced eye-related symptoms and has already recovered. And the dairy worker who tested positive for the virus in Texas in April only experienced eye redness as well, was treated with an antiviral medication for the flu, and is recovering. 

Is H5N1 bird flu in the milk we consume?

The Food and Drug Administration has found traces of H5N1 bird flu virus in raw or unpasteurized milk. However, pasteurized milk is safe to drink. 

Pasteurization, the process of heating milk to high temperatures to kill harmful bacteria (which the majority of commercially sold milk goes through), deactivates the virus. In 20 percent of pasteurized milk samples, the FDA found small, inactive (not live nor infectious) traces of the virus, but these fragments do not make pasteurized milk dangerous.

In a recent Infectious Diseases Society of America briefing, Dr. Maximo Brito, a professor at the University of Illinois College of Medicine, said that it’s important for people to avoid “drinking unpasteurized or raw milk [because] there are other diseases, not only influenza, that could be transmitted by drinking unpasteurized milk.” 

What can I do to prevent bird flu?

While the risk of H5N1 infection in humans is low, people with exposure to infected animals (like farmworkers) are most at risk. But there are several actions you can take to stay protected. 

One of the most important things, according to Sykes, is taking the usual precautions we’ve taken with COVID-19 and other respiratory viruses, including frequent handwashing, especially before eating. 

“Handwashing and mask-wearing [are important], just as we learned from the pandemic,” Sykes adds. “And it’s not wearing a mask at all times, but thinking about high-risk situations, like when you’re indoors in a crowded environment, where transmission of respiratory viruses is much more likely to occur.” 

There are other steps you can take to prevent H5N1, according to the CDC:

• Avoid direct contact with sick or dead animals, including wild birds and poultry.
• Don’t touch surfaces that may have been contaminated with animal poop, saliva, or mucus. 
• Cook poultry and eggs to an internal temperature of 165 degrees Fahrenheit to kill any bacteria or virus, including H5N1. Generally, avoid eating undercooked food. 
• Avoid consuming unpasteurized or raw milk or products like cheeses made with raw milk. 
• Avoid eating uncooked or undercooked food.
• Poultry and livestock farmers and workers and bird flock owners should wear masks and other personal protective equipment “when in direct or close physical contact with sick birds, livestock, or other animals; carcasses; feces; litter; raw milk; or surfaces and water that might be contaminated with animal excretions from potentially or confirmed infected birds, livestock, or other animals.” (The CDC has more recommendations for this population here.)

Is there a vaccine for H5N1?

The CDC said there are two candidate H5N1 vaccines ready to be made and distributed in case the virus starts to spread from person to person, and the country is now moving forward with plans to produce millions of vaccine doses.

The FDA has approved several bird flu vaccines since 2007. The U.S. has flu vaccines in stockpile through the National Pre-Pandemic Influenza Vaccine Stockpile program, which allows for quick response as strains of the flu virus evolve.  

Could this outbreak become a pandemic?

Scientists and researchers are concerned about the possibility of H5N1 spreading among people and causing a pandemic. “Right now, the risk is low, but as time goes on, the potential for mutation to cause widespread human infection increases,” says Sykes. 

“I think this virus jumping into cows has shown the urgency to keep tracking [H5N1] a lot more closely now,” Peter Halfmann, research associate professor at the University of Wisconsin-Madison’s Influenza Research Institute tells PGN. “We have our eyes on surveillance now. … We’re keeping a much closer eye, so it’s not going to take us by surprise.”

This article first appeared on Public Good News and is republished here under a Creative Commons license.