Even after almost 4 months, the virus survives in cheese made with non-pasteurized milk. However, more acidic cheeses, such as feta, did not show detectable virus.
A new published in Nature Medicine from Cornell University found that the highly pathogenic avian influenza virus (H5N1) can persist for months in certain types of unpasteurized milk cheeses. However, research has also revealed that more acidic cheeses, such as feta, neutralize the virus effectively.
The study examined how long the H5N1 virus can remain infectious in raw milk cheeses. The results show that, even after 120 days of maturation at 4°Cwhich is twice the time required by US food safety regulations, infectious viral particles were still present in some cheese samples, says .
Principal investigator Diego Diel, professor of virology at Cornell University’s College of Veterinary Medicine, said the work was motivated by previous studies showing that cows infected with the H5N1 virus eliminate large amounts of the virus in milk and that it can survive in refrigerated raw milk for long periods.
According to current regulations in the United States, raw milk cheese must be aged for at least 60 days to eliminate bacteria harmful. However, these findings suggest that this rule may not be enough to disable certain viruses. Research has found that pH plays a critical role in determining virus survival.
Cheeses with a pH between 5.8 and 6.6, such as cheddar and camembert, retained the live H5N1 virus. In contrast, cheeses with a pH of 5 or less, including highly acidic varieties like feta, did not present detectable virus.
To reduce risks, the team recommends testing milk for H5N1 before cheese production and exploring low-temperature treatments that can inactivate the virus. without compromising flavor and texture appreciated by producers of unpasteurized milk cheese.
According to the team, more research is needed to understand how viral particles interact with different cheese environments and how small adjustments in acidity can prevent future risks of contamination.
