Scientists have learned about the persistence of avian flu in raw milk cheese

According to a new study, cheese products made from contaminated raw milk may contain the infectious avian influenza virus. This creates potential health risks for consumers. This is reported by the Medical Xpress magazine.

On the other hand, the virus was not detected in samples of raw milk cheese with high acidity. Such waters of the product include feta.

"In this study, we specifically studied the stability or persistence of the highly pathogenic H5N1 avian influenza virus in raw milk cheese products. This study was initiated in connection with previous work that demonstrated a high level of virus release from the milk of infected cows, as well as the fact that we had previously shown that the virus survives in chilled raw milk for a long time," said Professor of Virology at the Department of Population Medicine and Diagnostic Sciences and director of the Virology laboratory at The Diagnostic Center for Animal Health (AHDC) at the College of Veterinary Medicine (CVM), senior author Diego Dil.

Although the Food and Drug Administration (FDA) requires raw milk cheese to be aged for at least 60 days at +35 degrees Fahrenheit or higher, the authors of the study discovered the infectious virus after 120 days of maturation at +39 degrees Fahrenheit. The required 60-day aging process is aimed at eliminating pathogenic bacterial contaminants potentially present in the product.

It is specified that the acid is indicated by the level of the acidity activity index (pH) less than seven. At the same time, the pH of most cheeses ranges between 5.4, like cheddar, and seven, like camembert, while feta reaches a level of 4.6 or even lower.

The study showed that raw milk cheese products contain a viable avian influenza virus if the cheese was made from infected raw milk and the pH of the cheese was between 5.8 and 6.6. At the same time, the virus was not detected in sour cheeses with a pH of five or lower.

Possible steps to prevent contamination of raw milk cheese products include testing the milk before making the cheese and using the product only without the virus. Another option is to heat the milk at sub-pasteurization temperatures before using it. According to Deal, this can preserve the necessary qualities of cheese production from raw milk and effectively inactivate the virus.

"The work we have done on H5N1 (the subtype that causes avian influenza. It is crucial to provide practical, timely, and data—based knowledge and recommendations to the dairy industry in the context of this outbreak, which has affected a significant portion of the U.S. milk supply, and allows raw milk cheese producers to reduce the risk," said Associate professor of Dairy Microbiology and director of the Quality Improvement Program. milk at the Department of Food Sciences in the College of Agriculture and Natural Sciences, study co-author Nicole Martin.

Although more research is needed, Diehl noted that the liquid matrix of milk probably allows the virus to have more contact with the mucous membranes in the pharynx, whereas cheese products may have less contact with cells in the area where the virus can cause infection.

In the study, the team developed an experimental model in the laboratory, where they produced and tested 5g mini cheeses made from raw milk infected with the H5N1 virus. Diehl stressed that all four cheddar samples received from the company were positively tested for H5N1.

The acidity of cheese is usually achieved through direct acid treatment or the addition of cultures of lactic acid bacteria that use lactose in milk to form lactic acid. Martin clarified that this acid reduces the pH of milk and, depending on how far this fermentation allows, determines how low the level of the acidity activity indicator will be.

Earlier, on December 5, 2023, immunologist Nikolai Kryuchkov spoke about the dangerous evolution of the avian influenza virus. According to him, the problem lies in the fact that the population is not ready for new serotypes, since there is no previous immunity.

All important news is on the Izvestia channel in the MAX messenger.