In a recent study, researchers found that small amounts of infectious bird flu virus remained detectable in raw milk samples after undergoing standard pasteurization treatment.
This research, conducted under experimental conditions in a laboratory, should not be interpreted as a reflection of the safety of the U.S. milk supply, according to the authors from the U.S. National Institute of Allergy and Infectious Diseases (NIAID) Rocky Mountain Laboratories, according to Times.
The findings, published in the New England Journal of Medicine, involved spiking raw milk samples with high levels of the bird flu virus. The virus used in the experiments was isolated from the lungs of a deceased mountain lion and mixed with raw, unpasteurized cow milk samples. These samples were then heat-treated at 63 degrees C (145.4 degrees F) and 72 degrees C (161.6 degrees F) for varying durations.
When treated at 72 degrees C for 20 seconds, which is five seconds longer than the industry standard for pasteurization, small amounts of infectious virus were detected in one of three samples. “This finding indicates the potential for a relatively small but detectable quantity of H5N1 virus to remain infectious in milk after 15 seconds at 72 degrees C if the initial virus levels were sufficiently high,” the researchers noted. told by Reuters.
At 63 degrees C, a marked decrease in infectious H5N1 virus levels was observed within 2.5 minutes, suggesting that the standard industry pasteurization process of 30 minutes at this temperature would eliminate the infectious virus.
However, the researchers emphasized that their experimental conditions do not perfectly replicate large-scale industrial pasteurization processes. They called for further studies using commercial pasteurization equipment to validate their findings.
Importantly, the study authors cautioned that raw milk from cows infected with H5N1 influenza might differ in composition or contain the virus inside cells, potentially impacting the effectiveness of heat treatment. as reported by CBS News.
In March, U.S. dairy cows were found to be infected with bird flu, leading the U.S. Food and Drug Administration to survey pasteurized retail milk samples and estimate that a fifth of the U.S. milk supply contained strands of the virus. The agency has maintained that pasteurized milk is safe to drink.
The researchers also highlighted that it remains unknown whether ingesting the active H5N1 virus in milk could cause illness in humans.
