Cornell Study Warns That H5N1 Bird Flu Virus Can Persist in Cheese Made from Raw Milk
Nikhil Prasad Fact checked by:Thailand Medical News Team Mar 18, 2025 6 hours, 36 minutes ago
Medical News: Scientists Warn of Bird Flu Risk in Certain Cheeses
A new study conducted by researchers from Cornell University-USA, in collaboration with food scientists and dairy microbiologists, has revealed that the highly pathogenic avian influenza (HPAI) H5N1 virus, commonly known as bird flu, can persist in cheese made from raw milk for extended periods. The findings raise serious public health concerns, especially for consumers who prefer unpasteurized dairy products.
Cornell Study Warns That H5N1 Bird Flu Virus Can Persist in Cheese Made from Raw Milk
While the U.S. Centers for Disease Control and Prevention (CDC) maintains that the overall risk of H5N1 to the general population remains low, the discovery of the virus in dairy products has heightened fears about potential human exposure. This
Medical News report sheds light on the persistence of the virus in raw milk cheese and the possible risks it poses.
How the Study Was Conducted
The study, published on March 14, was funded in part by the U.S. Food and Drug Administration (FDA). Researchers analyzed the stability of the H5N1 virus using two distinct approaches. First, they created a controlled model using raw milk deliberately spiked with the virus at varying pH levels. Second, they examined commercial raw milk cheese that had been inadvertently produced with naturally contaminated raw milk. The cheeses analyzed included cheddar, which had undergone the required 60-day aging period mandated by U.S. food safety regulations for raw milk cheeses.
According to the study, while raw milk itself has been shown to harbor the virus for up to eight weeks under refrigeration, the researchers aimed to determine whether the cheese-making and aging process would effectively neutralize the virus. Their results revealed that H5N1 exhibited "remarkable stability" and remained infectious in raw milk cheese even after the 60-day aging period, particularly in cheese samples with higher pH levels (pH 6.6 and 5.8). However, cheeses that were acidified to a pH of 5.0 or lower effectively inactivated the virus, preventing its survival.
Key Findings: Virus Stability in Raw Milk Cheese
The study demonstrated that H5N1 virus stability was heavily influenced by the acidity of the cheese:
-Cheese with pH 6.6 and 5.8: The virus remained detectable throughout the cheese-making process and persisted for up to 60 days of aging.
-Cheese with pH 5.0: The virus did not survive the production process, indicating that increased acidity can effectively neutralize H5N1.
-Temperature Effects: Sub-pasteurization treatment (at 130°F and above) inactivated the virus within 15 minutes, highlighting an alternative safety measure.
-Water Activity and pH Influence: During aging, the cheese's water activity gradually decreased, which slightly impacted viru
s survival but was not sufficient to eliminate it entirely at higher pH levels.
The researchers also validated their findings using commercially produced raw milk cheese samples. These samples, which were inadvertently contaminated with H5N1, were tested over a 60-day aging period. The results confirmed that the virus remained infectious throughout the mandatory curing process, raising concerns about the effectiveness of existing safety regulations for raw milk cheeses.
Implications for Public Health and Food Safety
The persistence of H5N1 in raw milk cheese presents significant challenges for food safety. The study underscores the potential for human exposure through the consumption of contaminated dairy products. While no human cases of H5N1 infection linked to raw milk cheese consumption have been documented to date, the possibility remains, particularly for individuals who frequently consume raw dairy products.
A past FDA survey revealed that approximately 4.4% of U.S. adults reported consuming raw milk at least once a year, with 1.6% consuming it regularly. Additionally, 1.6% of the population consumed raw milk cheeses. Given that the virus can survive in raw milk for extended periods and persist through cheese aging, the risk of exposure may be more significant than previously thought.
Recommendations for Consumers
Health experts recommend that consumers take the following precautions to minimize the risk of H5N1 exposure:
-Check Labels: While there is no federal requirement for labeling raw milk cheese, many products disclose whether they are made from pasteurized or unpasteurized milk. Consumers should choose pasteurized options to reduce risk.
-Consider Cheese Acidity: If opting for raw milk cheese, selecting varieties with lower pH levels (e.g., below 5.0) may lower the likelihood of H5N1 persistence.
-
Pasteurization is Key: The FDA reiterates that pasteurization is an effective method for inactivating H5N1 and other pathogens in dairy products.
-Be Cautious of Imported Cheeses: Some imported cheeses may not adhere to U.S. safety regulations and could pose a higher risk if made from unpasteurized milk.
Conclusion
The study provides crucial insights into the resilience of H5N1 in raw milk cheese, challenging existing assumptions that the cheese-making process naturally eliminates viral threats. The research highlights the need for additional mitigation steps, such as pH adjustments or thermization, to ensure food safety. Given the continued circulation of H5N1 in dairy herds and its increasing prevalence, regulatory agencies may need to revisit policies surrounding raw milk cheese production.
Public health authorities urge consumers to remain vigilant and make informed choices regarding raw dairy consumption. While pasteurization remains the most effective method for neutralizing pathogens, alternative strategies - such as pre-acidification of raw milk - could offer additional protection.
The study findings were published on a preprint server and are currently being peer reviewed.
https://www.biorxiv.org/content/10.1101/2025.03.13.643009v1.full
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