Ithaca: Cheese made from raw milk contaminated with avian influenza virus may retain infectious traces of the pathogen, raising concerns about food safety, media reports said on Tuesday. Researchers from Cornell University and the US Food and Drug Administration (FDA) found that highly pathogenic avian influenza (HPAI) H5N1 virus can persist in certain cheese products, even after the standard 60-day aging period required for raw milk cheeses, according to Science Daily.

According to Anadolu Agency, the research was initiated due to previous work demonstrating high levels of virus shedding in milk from infected cows. The news outlet quoted Diego Diel, senior author of the study and professor of virology at Cornell, as saying the study highlighted the persistence of the virus in cheese samples aged beyond the FDA guideline of 60 days. The virus remained viable for 120 days at 39F (4C) in some cheese samples, the researchers reported.

The study further revealed that cheese acidity plays a critical role in inactivating the virus. No infectious virus was found in samples with a pH of 5 or below, such as feta cheese, which naturally has a high acidity level. In contrast, cheeses with pH levels between 5.8 and 6.6 retained the virus, indicating a higher risk of transmission through these products.

Nicole Martin, co-author of the study and assistant research professor in dairy foods microbiology, emphasized the importance of the findings. "The work we've done on H5N1 is critical to providing practical, timely, data-driven knowledge and recommendations to the dairy industry," she said. To assess virus stability, the researchers created experimental cheeses using H5N1-spiked raw milk and analyzed commercial cheddar samples submitted by FDA officials, all of which tested positive for the virus.

The study also included ferret experiments to evaluate transmission risk. Ferrets that drank contaminated raw milk became infected, while those that consumed raw milk cheese showed no signs of infection. Diel suggested that the difference in infection rates could be due to how the body interacts with milk versus cheese, with milk's fluid nature potentially increasing contact with mucous membranes.

Additionally, the team investigated how cheese acidity develops, noting that lactic acid bacteria or direct acidification lowers the pH by converting milk sugars into acid. This acidification method was used in lab experiments to test cheese safety. The study, published in Nature Medicine and supported by the FDA and the New York State Department of Agriculture and Markets, included contributions from authors Mohammed Nooruzzaman, Pablo Sebastian Britto de Oliveira, Salman Butt, Samuel D. Alcaine, and Stephen Walker.