An individual in the United States has contracted an extremely contagious strain of avian flu for the first time, officials confirmed on Thursday.

The individual—a man who works on a commercial farm in Colorado—was culling poultry when he likely contracted H5N1, according to a press release from the Colorado Department of Health. 

“The adult male, who is younger than 40, is largely asymptomatic, reporting only fatigue,” the department said. “He is now isolating and receiving the influenza antiviral drug oseltamivir (Tamiflu) per [U.S. Centers for Disease Control and Prevention] guidance. Scientists believe the risk to people is low as H5 flu viruses spread among wild birds and poultry. They do not normally infect humans nor spread person to person. There are currently no known cases of this H5 flu virus spreading among people. There are no other confirmed human cases in Colorado or the United States at this time.”

The department confirmed that the man who contracted the virus was directly exposed at a commercial farm in Montrose County. The flock was euthanized and disposed of, following guidance from the U.S. Department of Agriculture and the Colorado Department of Agriculture.

“While human infections of the H5 viruses are rare, direct exposure to infected birds increases that risk,” the health department said. “Infected birds shed flu viruses in their saliva, mucous, and feces.”

Public health officials in the United Kingdom confirmed the first case of the H5 virus being spread to a human in January 2022. That individual also had direct contact with infected birds and was asymptomatic.

From Wyoming to Maine, an outbreak of the highly contagious bird flu has swept across the U.S. this year. Millions of chickens and turkeys from infected commercial and backyard flocks in 22 states have been killed. https://t.co/A1FHaH8dGL

— The New York Times (@nytimes) April 28, 2022

Poultry farmers have been dealing with various outbreaks of avian flu (Highly Pathogenic Avian Influence, HPAI, also known as H5N1) that may have claimed as many as 24 million birds so far—either who had the virus or were killed to prevent its spread. NBC News reports that the virus has been identified in commercial and backyard birds in 29 U.S. states and in wild birds in 34 U.S. states.

“An outbreak at a lake outside Chicago is believed to have killed more than 200 birds, and at least three bald eagles died from the virus in Georgia,” according to NBC News. “Millions of chickens and turkeys have been killed to prevent the virus’s spread, prompting a surge in poultry prices.”

The U.S. Department of Agriculture (USDA) issued a press statement on 30 March 2022, confirming the spread of HPAI in the United States and that it was working with U.S. state animal health officials on joint incident responses. 

“As part of existing influenza response plans, federal and state partners are working jointly on additional surveillance and testing in areas around the affected flocks,” the USDA said. “The United States has the strongest AI surveillance program in the world, and USDA is working with its partners to actively look for the disease in commercial poultry operations, live bird markets, and in migratory wild bird populations.”

Along with practicing “good biosecurity,” the USDA encouraged bird owners to prevent contact between their birds and wild birds—and report sick birds or unusual bird deaths to officials.

Health officials and scientists are concerned that this virus will continue to pass from wild birds to poultry farms, making it difficult to stop it from spreading.

“While chickens and turkeys with the virus quickly sicken and die, some waterfowl can remain healthy with the virus and carry it long distances,” NPR reports. “Scientists believe that wild migratory birds brought this virus to North America a few months ago. Since then, more than 40 wild bird species in more than 30 states have tested positive. This strain of bird flu virus has turned up in everything from crows to pelicans to bald eagles.”

The U.S. Centers for Disease Control and Prevention (CDC) has also been monitoring 500 humans who have been exposed to infected birds. Some had developed flu-like symptoms, but until Thursday none had tested positive for the virus.

News of the transmission was concerning as the COVID-19 pandemic began with a virus passing from a bat at a wet market in China to a human. As of press time, the World Health Organization (WHO) had confirmed more than 500 million cases of COVID-19 around the world and more than 6 million deaths from the disease. 

Research published this week in the journal, Nature, also found that climate change will likely result in more new viruses being spread by animal species—raising the risk of those diseases jumping from animals to humans. 

The researchers model examined how more than 3,000 mammal species might migrate and share viruses during the next 50 years if the planet warms by 2 degrees Celsius. 

“They found that cross-species virus spread will happen over 4,000 times among mammals alone. Birds and marine animals weren’t included in the study,” the Associated Press reports. “Researchers said not all viruses will spread to humans or become pandemics the scale of the coronavirus but the number of cross-species viruses increases the risk of spread to humans.”