Laboratory Findings

Research by the National Institute of Allergy and Infectious Diseases (NIAID) reveals that heat treatment significantly reduces the amount of infectious H5N1 influenza virus in raw milk. However, trace amounts of the virus remained in samples with high initial virus levels when treated at 72 degrees Celsius (161.6 degrees Fahrenheit) for 15 seconds—a standard pasteurization method. The study, published in the New England Journal of Medicine, emphasizes that these results were obtained under laboratory conditions and may differ from large-scale industrial pasteurization processes.

Recent Outbreak and Monitoring

In March 2024, a highly pathogenic avian influenza virus, HPAI H5N1, was detected among dairy cows in Texas, affecting 95 cattle herds across 12 states and resulting in three human infections among farm workers. Although there is no evidence that the virus can spread from person to person, public health officials continue to monitor the situation as part of pandemic preparedness efforts.

Experiment Details

Scientists at NIAID’s Rocky Mountain Laboratories investigated the stability of the H5N1 virus in raw milk at 63℃ (145.4 degrees Fahrenheit) and 72℃, the temperatures commonly used in commercial dairy pasteurization. The virus was isolated from a dead mountain lion in Montana and mixed with raw cow milk. The milk was then heat-treated at these temperatures for varying durations and tested for live virus.

The study found a significant decrease (1010-fold) in infectious H5N1 levels at 63℃ within 2.5 minutes, suggesting that standard bulk pasteurization of 30 minutes would eliminate the virus. At 72℃, a marked decrease (104-fold) was observed within five seconds, but small amounts of the virus were still detectable after 20 seconds in one of three samples. This indicates that a small but detectable quantity of H5N1 virus could remain infectious in milk treated at 72℃ for 15 seconds if initial virus levels are high.

Limitations and Safety

The researchers caution that their results should be replicated with commercial pasteurization equipment and note that the study used raw milk spiked with H5N1, which may differ from milk from infected cows. They also highlight the need for further studies to understand whether ingesting live H5N1 in raw milk could cause illness in humans.

According to the U.S. Food and Drug Administration (FDA), current evidence supports the safety of the commercial milk supply. An initial survey of 297 retail dairy products across 17 states found no viable virus. The FDA and USDA are conducting additional studies to validate pasteurization methods, with results to be released as they become available.

Highlights

• Heat Treatment Effectiveness: Heat treatment at 72℃ significantly reduces H5N1 in raw milk, though trace amounts may remain if initial virus levels are high.
• Recent Outbreak: HPAI H5N1 outbreak in Texas affected 95 cattle herds across 12 states, with three human infections reported.
• Laboratory Study: NIAID's study used viral isolates from a mountain lion and found significant virus reduction at 63℃ and 72℃, with some limitations noted.
• Safety Assurance: FDA surveys confirm the safety of the commercial milk supply, with no viable virus detected in retail dairy products.

Data Source: F Kaiser et al. Inactivation rate of highly pathogenic avian influenza H5N1 virus (clade 2.3.4.4b) in raw milk at 63 and 72 degrees Celsius. The New England Journal of Medicine DOI: 10.1056/NEJMc2405488 (2024).

https://www.nih.gov/news-events/news-releases/nih-funded-intervention-did-not-impact-opioid-related-overdose-death-rates-over-evaluation-period </