H5N1 influenza surveillance on 14 California dairy farms has uncovered new, potential transmission routes beyond tainted milk. The virus has been detected in the air, in wastewater, and in cows showing no clear signs of illness.
Infectious H5N1 was found in air samples from milking parlors, suggesting the virus can become airborne. Viral RNA was also present in the exhaled breath of cows, raising the possibility of respiratory spread.
Farm wastewater tested positive for live virus. This water, which may contain discarded milk, is often reused for irrigation or flushing pens, potentially creating virus-laden aerosols. The wastewater can also attract birds and other animals.
Crucially, milk sampling revealed many infected cows had no symptoms, complicating detection efforts. This subclinical infection could allow the virus to circulate undetected within herds.