Swiss cows have so far escaped the H5N1 global avian flu. But if it affects the dairy herds, the emblematic cheeses of the country – from the vacherin raclette – could be threatened. An assumption not so wacky, because the H5N1 has already been detected in American dairy cows.
Most traditional Swiss cheeses are made from raw milk. This tradition makes them more risky for consumers, because these cheeses avoid the pasteurization process that kills bacteria and harmful viruses.
Although the cheese industry and the Swiss government have taken measures to minimize health risks linked to the consumption of unpasteurized milk, a new threat weighs on this production process of several centuries.
In March 2024, the H5N1 virus-a highly pathogenic avian influenza virus (IAHP) virus for birds and sometimes fatal for humans-was detected in dairy cows in the United States, thus marking the world known in cows. If infected cattle generally develop only a benign form of the disease, the epidemic has alerted the potential risks for agricultural workers and food security.
An American epidemic
From March 2024 to July 2025, cases of H5N1 were detected in more than a thousand dairy herds in 17 US states and 41 workers in the sector would have been infected with exposure to sick or infected cows, according to the US government data.
The disease, suspected of being due to contact with infected wild birds, was confirmed by scientists from the US government after farmers found that cows lost appetite and produced abnormal and discolored milk.
In April 2024, scientists detected IAHP in 57.5% of the 275 raw milk samples taken from herds of the four affected states: Texas, Kansas, Idaho and New Mexico. Additional analyzes have revealed that a quarter of the samples contained the H5N1 strain, and an additional study showed that pasteurization neutralized the pathogen in artificially contaminated raw milk.
The cheese also affected
The American Food and Drug Administration (FDA) also tested refined raw milk cheeses for 60 days to detect the presence of the H5N1 virus. Out of 110 samples analyzed in early 2025, 96 proved to be negative and the results of 14 samples are still pending. Although the results suggest that refined raw milk cheeses could be free from the virus, a Study funded by the FDA and conducted by Cornell University has shown that it can survive in certain refined cheeses if their level of acidity is too low.
“Our study highlights the potential risks to public health related to the consumption of raw milk cheese, highlighting the need for additional mitigation measures in the production of cheese to prevent human exposure to infectious virus,” wrote scientists in an article published in March on the Biorxiv platform, which distributes research articles before they are evaluated by peers and officially published.
A first Swiss study
In Switzerland, a study On the potential impact of avian flu on raw milk products was only published in June of this year by the Agroscope Agricultural Research Institute and the Institute of Virology and Immunology (IVI). Scientists have tested Swiss cheese prepared from raw milk, to which the H5N1 virus had been injected, isolated from the milk of dairy cows infected in Texas. They discovered that, in non -pasteurized milk, the H5N1 virus can survive the cheese manufacturing processes if the temperature during production remains less than 50 degrees.
In general, the raw milk used for the manufacture of hard and extra-dure cheeses is heated to approximately 51-58 degrees during production, a process that reduces pathogens and makes the final product more specific to consumption. On the other hand, the raw milk used for the manufacture of soft cheeses is heated only about 35 degrees, and less than 50 degrees for most media cheeses. The pre-cabinet temperatures of the most common raw milk cheeses can reach 57 degrees for the Gruyère, 52-54 degrees for the Emmental, 43-45 degrees to appear it and 42 degrees for the raclette.
Acidity, salt concentration or the amount of water available for microbial growth (quantity of water during manufacturing) can also determine the survival of the active virus.
Contacted by Swissinfo, the Federal Office for Food Safety and Veterinary Affairs (OSV) replied that it was aware of the study but that it did not see the need to take preventive measures for the moment, because there is currently no documented cases of H5N1 in dairy cows in Switzerland.
Article original: Anand Chandrasekhar (SWI)
French adaptation: furr
