Bird flu, or H5N1 virus, in unpasteurized milk is stable on metal and rubber components of commercial milking equipment for at least one hour, increasing its potential to infect people and other animals, report researchers from the University of Pittsburgh School of Medicine and Emory University in Emerging Infectious Diseases. 

The study underscores the heightened risk of bird flu exposure for dairy farm workers and signals the need for wider adoption of personal protective equipment, including face shields, masks and eye protection.

“Dairy cows have to be milked even if they are sick, and it has not been clear for how long the virus contained in residual milk from the milking process remains stable on the equipment,” said lead author Valerie Le Sage, Ph.D., research assistant professor of microbiology and molecular genetics at the Center for Vaccine Research at Pitt. “It is concerning that the virus in unpasteurized milk can remain stable for hours and potentially infect farm workers or spread from animal to animal.”

Clinical symptoms of bird flu can range from mild fever and cough to shortness of breath and pneumonia and can be lethal. Since March 2024, when the bird flu virus was first detected in dairy cattle in the U.S., the virus has spread across state lines and infected at least 3 people. While, according to the U.S. Center for Disease Control and Prevention, the current risk to the general public remains low, flu viruses can quickly adapt to spreading from person to person.

To understand the potential for spread from cattle to dairy farm workers, researchers looked at the stability of infectious flu virus particles in unpasteurized milk droplets on metal and rubber components of commercial milking equipment.

In a lab environment that mimicked the humidity and temperature of outdoor milking parlors in Texas, H5N1 virus particles suspended in milk remained stable on metal and rubber for over one hour. Particles of H1N1 virus, or swine flu, which behaves similarly to H5N1 in the lab, stayed infectious for at least 3 hours on rubber and for at least 1 hour on stainless steel.

“Our data supports that milking equipment surfaces can stay contaminated for a long time, increasing the potential spread from a sick animal to a person,” said Le Sage. “These findings underscore the importance of face shields, masks and eye protection, and enhanced sanitization of equipment between cows to reduce the risk to workers and to minimize the spread between the animals.”

Other authors of this research are Douglas Reed, Ph.D., and Paul Duprex, Ph.D., both of Pitt; and A.J. Campbell, Ph.D., and Seema Lakdawala, Ph.D., both of Emory University.