Bird Flu: How milk can spread the H5N1 Avian influenza
bird flu, is spreading rapidly through milk on US dairy farms. Since March, the H5N1 virus has infected over 850 cattle herds across 16 states, and at least 60 people, mostly farmworkers. California is the current outbreak epicenter.
How the virus spreads
Scientists initially suspected airborne transmission, but data points to milk as the primary culprit. The H5N1 virus reproduces rapidly in the udders of infected cows, leading to high pathogen levels in milk. Infected milk droplets can splash into workers’ faces, contaminate equipment, and spread the virus to other cows. While pasteurization neutralizes the virus, traces have been found in retail samples of raw milk in California, raising public health concerns.
Modern dairy practices and risks
The U.S. dairy industry, with over 9 million cows producing 600 million pounds of milk daily, has undergone significant consolidation. Large-scale farms dominate, with 65% of dairy cows now living on farms with 1,000 or more animals. These operations milk cows multiple times daily using shared equipment, which can facilitate virus spread.
At Heeg Brothers Dairy in Wisconsin, workers milk 1,050 cows three times a day in a 28-stall parlor. The process involves manual stimulation, disinfection, and attaching milking claws. However, milk droplets from infected cows can linger on equipment and potentially infect others. “During milking, the teat end is open, potentially even relaxed,” explained Dr. John Barlow, a veterinary epidemiologist at the University of Vermont.
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