Highly pathogenic avian influenza, or H5N1, remains infectious in raw milk and cheese products, presenting new risks for consumers of these products and the farmers who make them, according to new research from Cornell University.
According to the study, which was published late last year in the journal Nature Medicine, ferrets that consumed H5N1-contaminated raw milk fell ill with the virus, while those fed raw-milk cheeses did not. However, the paper cautioned that H5N1 remains infectious in raw-milk cheese under specific conditions. The virus survived up to 120 days of aging in cheeses made at pH levels of 6.6 and 5.8.
A pH level of 5 killed the virus — but cheese is not typically made at this pH, according to Dr. Diego Diel, DVM, director of Cornell University's Animal Health Diagnostic Center.
“The stability of the virus in raw-milk cheeses under these conditions is remarkable, as the virus survived much longer than the minimum aging period of 60 days required by FDA for raw milk cheeses,” Diel said in an email.
The study also found that the H5N1 virus can survive in refrigerated raw milk for up to 8 weeks.
The Cornell University research group participated in the first detection of H5N1 infection in dairy cows, and was one of the first labs to detect infectious virus in milk from cows that had fallen ill. They initiated study of the virus in raw and pasteurized milk products immediately after it was detected in milk, Diel said.
Researchers at Cornell University are now working to identify the minimum level of acidification needed to inactivate the virus, in case slight changes to the cheesemaking process could reduce the risk of infection. The study results point to a need for increased testing or treatment of dairy products, Dr. Diel said.
“Because the virus continues to circulate among multiple hosts, producers should closely monitor for any clinical signs that may indicate infection.” Diel said. “Early detection enables timely implementation of control strategies to limit spread, minimize economic losses and reduce public health risks.”
