The ongoing bird flu outbreak in the US has alarmed public health officials as it spreads rapidly through large dairy farms, infecting both cows and workers, the New York Times reports.
Since March, the H5N1 virus has reached more than 700 herds across 15 states and infected at least 58 people, mostly farm workers. California has become the epicenter of the crisis, with cases mounting among humans and livestock.
Experts initially suspected airborne transmission, but evidence now suggests that the virus primarily spreads through milk. It replicates in the udders of infected cows, producing milk with high levels of the pathogen. Splashes of contaminated milk can expose dairy workers or contaminate equipment, facilitating the spread.
Although pasteurization neutralizes the virus, it has been detected in retail samples of raw milk in California, raising public health concerns. Seema Lakdawala, a virologist at Emory University, emphasized the challenges of milk-based transmission, calling it “hugely problematic.”
Milking operations at large dairy farms offer insight into why containing milk-borne pathogens is difficult. At Heeg Brothers Dairy in Wisconsin, workers manually stimulate milk flow, disinfect teats, and attach milking claws. Each claw is not cleaned between cows, potentially spreading the virus through lingering milk droplets.
Milk meters transport the liquid through pipelines to be cooled and stored, but splashes from the milking claws can pose a risk.
“During milking, the teat end is open, potentially even relaxed,” said Dr. John Barlow, a veterinary epidemiologist, highlighting the vulnerability.
Cleaning routines are thorough, but with farms milking thousands of cows daily, any lapse could allow the virus to persist.
Robotic milking parlors may reduce transmission risks by automating the milking process. At Heeg Brothers Dairy, cows approach robotic stations independently, where cameras and sensors disinfect and milk the cows without human contact. These systems rinse themselves with iodine between milkings, limiting cross-contamination.
While robotic systems are not foolproof, they minimize human interaction with potentially infected cows, reducing the likelihood of cow-to-human transmission.
The outbreak’s rise coincides with concerns over potential leadership changes in health agencies. Robert F. Kennedy Jr., a known advocate of raw milk, has suggested pausing infectious disease research, sparking debate over federal oversight during the outbreak.
Despite efforts to contain the virus, experts warn that the risks remain significant.
“Bird flu is just one more challenge,” said Jay Heeg, a third-generation dairy farmer.
