A pilot study conducted by University of California, Davis researchers has identified a new way to inactivate the H5N1 bird flu in milk.
The discovery could help curtail the spread of the virus from contaminated raw milk that’s disposed of or fed to calves, boosting farm biosecurity.
The method is also cheaper than pasteurization and can be easily leveraged on farms that do not pasteurize waste milk. According to USDA data, less than 50% of large dairy farms currently pasteurize waste milk, and an even lower share of small and medium dairies do so.
So what is this new alternative for inactivating the H5N1 virus in milk?
Milk acidification
The UC Davis researchers considered two alternatives to pasteurization of waste milk – acidification and the lactoperoxidase system (LP system).
The LP system activates the enzyme lactoperoxidase, which is naturally present in milk, has an antimicrobial action, and is GRAS-certified by the FDA for use in milk, the researchers explain in the paper.
Meanwhile, acidification has become a common method of lowering the pH of milk to levels that inhibit bacterial growth and survival.
In laboratory trials, the researchers proved that using citric acid to acidify milk to a pH of 4.1 to 4.2 inactivates the bird flu virus in 6 hours.
In addition, the low pathogenic bird flu strain (LPAI H6N2) was better inactivated in milk with a higher fat content.
According to the paper, studies conducted on products other than milk have achieved similar findings on the inactivation of influenza A viruses – but when it comes to milk, this is likely a first of its kind discovery.
Who pasteurizes waste milk?
In the US, around 44% of large farms (500 cows or more), 3% of medium operations (100 - 499 cows), and 1% of small operations (fewer than 100 cows) pasteurize waste milk before feeding it to calves.
“Our study supports the effectiveness of milk acidification for the inactivation of H5N1 in milk, serving as a potential alternative to pasteurization for the inactivation of HPAI H5N1,” the UC Davies researchers concluded.
“For the H5N1 milk-acidification trial, we observed that milk acidification resulted in a significant reduction in viral load.
“Our findings support an ideal mean target pH for milk acidification of 4.1, avoiding a pH above 4.2 due to the potential reduced effect on H5N1 inactivation in milk.
“To our knowledge, this is the first report for the complete inactivation of HPAI H5N1 in whole milk using milk acidification.”
Source:
In-laboratory inactivation of H5N1 in raw whole milk through milk acidification: Results from a pilot study
Authors: Crossley, M., Beate et al
Published: Journal of Dairy Science, Volume 108, Issue 3, P2264-2275, March 2025
