By Scout Nelson
A new study published in PLOS Biology has revealed possible new sources of H5N1 avian influenza transmission on dairy farms in California. Researchers found infectious virus particles in the air of milking parlors and wastewater systems, along with viral RNA in cows’ breath and milk. The findings raise concerns about additional exposure risks for farm workers, livestock, wildlife, and surrounding farm environments.
The study was led by researchers from Emory University and focused on 14 dairy farms in California that tested positive for H5N1 avian influenza during 2024 and 2025. Scientists collected air, wastewater, and milk samples from farms located in two different regions of the state. According to the researchers, the results suggest there may be several possible transmission routes that have not been fully understood before.
“Highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b B3.13 virus was first detected in dairy cattle in March of 2024 and has since spread to 16 states,” they wrote. “Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms.”
In the first stage of the research, scientists examined five dairy farms. They discovered H5N1 viral RNA in milk tanks even before cows showed visible signs of illness. Researchers also analyzed 71 air samples and found positive results in four samples from milking parlors and two samples collected from cows’ exhaled breath.
Additional monitoring on nine farms showed viral RNA in 21 of 35 air samples. Scientists reported that airborne particles inside milking parlors included both very small submicron particles and larger aerosols. Four air samples contained infectious virus particles capable of spreading disease.
The study also detected H5N1 viral RNA throughout wastewater systems, including manure lagoons used by migratory birds and fields where cows graze. Two wastewater samples contained detectable infectious virus after laboratory testing.
“Together, these results highlight the extensive environmental contamination of H5N1 on affected dairy farms and identify additional sources of viral exposure for cows, peridomestic wildlife, and humans,” the authors wrote. “Dairy parlors, which are often enclosed spaces and where aerosolization of milk occurs, pose the greatest threat from inhalation of the virus to dairy farm workers.”
Photo Credit: gettyimages-minchen-liang-eyeem
Categories: Minnesota, Livestock, Dairy Cattle