Study Confirms Persistence of Bird Flu in Raw Milk Cheese

Recent research highlights the potential health risks associated with consuming raw milk cheese contaminated with avian influenza viruses. The study, published in Nature Medicine, focused on the stability and infectivity of the highly pathogenic H5N1 influenza virus in raw milk and cheese products. Findings revealed that when raw milk is contaminated, the resulting cheese can harbor the infectious virus, especially in varieties with a pH above 5.8, which provides a conducive environment for viral survival.

In particular, the study demonstrated that raw milk cheeses with a pH between 5.8 and 6.6 tested positive for viable H5N1 virus, while more acidic cheeses with a pH of 5 or lower did not contain the virus. Interestingly, the research showed that the virus could survive even after 120 days of aging at refrigeration temperatures, which exceeds the 60-day minimum aging requirement mandated by the FDA for raw milk cheeses. This raises concerns about current safety standards.

Senior author Diego Diel emphasized that the virus’s survival in raw milk products could pose direct health risks, especially as the fluid nature of milk might lead to higher contact with mucous membranes, potentially facilitating infection. Conversely, cheese with a lower pH, such as feta, which typically has a pH below 5, did not support virus survival. The study suggests that testing milk before cheese production and heating raw milk at sub-pasteurization temperatures could reduce the risk of contamination without compromising the qualities prized by cheese makers.

Animal tests further supported these findings: ferrets fed contaminated raw milk showed infection, whereas those fed contaminated cheese did not, indicating that the cheese might be less infectious under certain conditions. The research involved creating mini cheeses with varying pH levels and testing commercial cheeses suspected of contamination, revealing the presence of H5N1 in actual products.

These findings underscore the importance of strict testing and safety protocols in raw milk cheese production to prevent the spread of avian influenza viruses, which could otherwise pose significant public health risks. The study advocates for more careful handling and processing of raw milk and highlights the need for continued research into virus inactivation methods suitable for the dairy industry.

Source: MedicalXpress