Bird flu may be airborne on US dairy farms, say scientists
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Infections in US dairy cattle came as a surprise in 2024, as bird flu was not known to affect the animals.
PHOTO: REUTERS
Apoorva Mandavilli and Emily Anthes
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WASHINGTON - The bird flu virus that has beset US dairy farms since early 2024 may be spreading through the air in so-called milking parlours and through contaminated wastewater, as well as from milking equipment, scientists have found.
The US Department of Agriculture has said that the virus spreads primarily from milking equipment or is carried by dairy workers and vehicles travelling between farms.
But in the new study, scientists found live virus in the air of milking facilities, suggesting that cows and farmworkers might have become infected by inhaling the pathogen.
The study was posted online last week and has not been peer-reviewed for publication.
But the results are consistent with those from other teams, who found that contaminated milking equipment might not explain all cases of bird flu observed on farms.
Just as people can become infected with the seasonal flu virus by touching a sick person, from contaminated surfaces or by inhalation, “there is no one way” that bird flu spreads, said Associate Professor Seema Lakdawala, a virus expert at Emory University who led the work.
The bird flu virus, called H5N1, was first detected in dairy cows in March 2024.
Since then, it has spread to more than 1,000 herds in 17 states, the majority of them in California, the nation’s leader in dairy production.
Bird flu has also infected dozens of people, hospitalising a few and killing one.
Federal officials have not held any briefings about the bird flu outbreak since US President Donald Trump took office in January.
The infections in dairy cattle came as a surprise in 2024, as bird flu was not known to affect the animals.
H5N1 appears to be particularly concentrated in the cows’ milk, turning it yellow and viscous.
Milking machines are often hooked up to many cows in quick succession and may not be thoroughly disinfected in between. The machines quickly became the suspected source of transmission on dairy farms.
Prof Lakdawala and her colleagues at first believed that milking machines would prove to be the main source.
They collected samples from air, wastewater, milking machines and cows on 14 California dairy farms that reported bird flu outbreaks in late 2024 and early 2025.
They found the virus in the milk of sick cows and on milking equipment.
To their surprise, researchers also found infectious virus in air samples collected from parlours while cows were being milked. THE NEW YORK TIMES
