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Researchers from the U.S. National Institute of Allergy and Infectious Diseases (NIAID) Rocky Mountain Laboratories recently conducted a study revealing that even after subjecting raw milk samples intentionally spiked with high concentrations of the bird flu virus to standard pasteurization methods, small quantities of infectious virus were still detectable. This finding, published in the prestigious New England Journal of Medicine, highlights potential concerns regarding the persistence of viral infectivity in dairy products under controlled laboratory conditions.

The experiment focused on assessing the resilience of the H5N1 influenza virus, initially isolated from the lungs of a deceased mountain lion, when introduced into raw, unpasteurized cow milk samples. These mixtures were then subjected to rigorous heat treatments at temperatures ranging from 63°C (145.4°F) to 72°C (161.6°F) for varying durations, simulating the industry-standard pasteurization processes.

Key observations included the detection of trace amounts of infectious virus in one out of three samples when exposed to an extended treatment of 72°C for 20 seconds—just five seconds beyond the conventional pasteurization duration at that temperature. This outcome suggests that even a slight deviation from standard pasteurization protocols may potentially leave behind residual infectious particles, albeit in minimal quantities.

Conversely, swift and significant reductions in infectious virus levels were noted within a mere 2.5 minutes of treatment at 63°C, reaffirming the efficacy of the established 30-minute pasteurization process at this temperature in eliminating viral infectivity from milk.

The study's authors cautioned against extrapolating these findings to broader implications for the safety of the U.S. milk supply, emphasizing the controlled experimental conditions and the need for further research. They pointed out that raw milk from naturally infected cows might differ in virus distribution and susceptibility to heat treatment compared to artificially spiked samples, potentially influencing the outcomes observed.

Earlier this year, concerns over avian influenza outbreaks among U.S. dairy cows prompted regulatory scrutiny, with the U.S. Food and Drug Administration (FDA) conducting assessments on retail milk samples. Despite detecting viral genetic material in a portion of the tested samples, the FDA reiterated that pasteurized milk remains safe for consumption, underscoring the effectiveness of routine pasteurization protocols in mitigating public health risks.

The implications of potential exposure to active H5N1 virus through milk consumption on human health remain a subject of ongoing investigation. Researchers stress the importance of replicating these experiments using commercial-scale pasteurization equipment to validate their findings under conditions more closely resembling industrial processes. This rigorous approach aims to provide actionable insights into optimizing dairy safety protocols and ensuring consumer confidence in milk products amidst evolving public health challenges.