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J Dairy Sci . In laboratory inactivation of H5N1 in raw whole milk through milk acidification: results from a pilot study

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  • J Dairy Sci . In laboratory inactivation of H5N1 in raw whole milk through milk acidification: results from a pilot study

    J Dairy Sci


    . 2025 Jan 29:S0022-0302(25)00051-7.
    doi: 10.3168/jds.2024-25985. Online ahead of print. In laboratory inactivation of H5N1 in raw whole milk through milk acidification: results from a pilot study

    Beate M Crossley 1 , Craig C Miramontes 2 , Daniel Rejmanek 3 , Rodrigo Gallardo 2 , Richard Pereira 4



    AffiliationsFree article Abstract

    Avian Influenza virus H5N1 2.3.4.4.b has recently been detected in cattle, with milk from infected animals reported to contain a high viral load, serving as a potential source for shedding and dissemination of this virus. Currently, pasteurization is the only widely recognized method for on-farm inactivation of H5N1 in milk. A current concern is that according to USDA data, less than 50% of large dairy farms pasteurize non-saleable milk, with a much lower percentage occurring in medium and small dairy farms. The objective of this pilot study was to evaluate the effect of milk acidification to a pH of ∼4.0 to 4.4 and lactoperoxidase system (LPS) on the inactivation of low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI) in raw whole milk. Initial trials in our study used the LPAI H6N2 virus as a surrogate for HPAI H5N1. For the milk acidification trials, citric acid was used to acidify milk. For evaluation of milk acidification and LPS, milk samples were inoculated with LPAI H6N2, with samples collected before and after treatment at various times. Evaluation of virus viability was conducted using specific-pathogen-free (SPF) embryonated chicken eggs and viral quantification using real-time quantitative PCR (RT-qPCR). Three acidification experiments were conducted using milk spiked with LPAI H6N2. Given the positive outcome observed in the inactivation of LPAI with citric acid, a fourth trial was conducted with milk containing a high load of H5N1 originating from actively infected cows. Our findings observed that MILK ACIDIFICATION with a pH between 4.1 and 4.2 resulted in the inactivation of LPAI H6N2 and HPAI H5N1 virus in milk after 6 h of treatment. Milk treatment with LPS was not effective for the inactivation of the H6N2 virus, and no further trials were conducted for this treatment option. This is the first study reporting the effectiveness of MILK ACIDIFICATION for the inactivation of HPAI H5N1 in milk originating from animals infected with H5N1. Milk acidification is an effective, accessible, and easy-to-use alternative to milk pasteurization, and future studies should evaluate the on-farm effectiveness of acidification of non-saleable milk to inactivate H5N1.

    Keywords: H5N1; milk acidification; non-saleable milk; viral inactivation.


  • #2
    Killing H5N1 in Waste Milk — An Alternative To Pasteurization

    Milk Acidification Provides Easy Way for Dairy Farms to Contain Bird Flu Virus
    • by Amy Quinton
    • February 13, 2025

    News Holstein calf feeds from a bottle of colostrum milk. UC Davis researchers have found that acidification of waste milk can kill H5N1, the virus that causes bird flu. (Richard Van Vleck Pereira / UC Davis)

    Pasteurization is the only widely recognized method of killing H5N1, the virus that causes bird flu, in milk. However, pasteurization can be expensive and fewer than 50% of large dairy farms pasteurize waste milk.

    Waste milk includes colostrum, the first milk after calving; milk from cows treated with antibiotics or other drugs; or any other factor that can make milk unsuitable and unsellable for human consumption. On farms, raw waste milk poses a potential risk of spreading avian flu, which so far has been confirmed in dairy cattle in 16 states.

    University of California, Davis, researchers have found that acidification can kill H5N1 in waste milk, providing dairy farmers an affordable, easy-to-use alternative to pasteurization of waste milk. The Journal of Dairy Science published the study.

    “There can be a quite significant cost to have pasteurization as an option on the farm,” said co-corresponding author and veterinary epidemiologist Richard Van Vleck Pereira, with the UC Davis School of Veterinary Medicine. “In our laboratory tests, we found that acidifying milk to a pH of 4.1 to 4.2 with citric acid effectively deactivates the virus.”

    The UC Davis research team will next conduct on-farm testing of milk acidification in waste milk containing H5N1. They will develop practical guidelines for farmers to implement acidification of waste milk as a protocol on the farm.

    A sustainable solution

    Pereira said citric acid is inexpensive. Acidified waste milk is also safe to be used to feed pre-weaned calves. The acidification process takes only six hours to fully kill the virus and doesn’t require refrigeration, further reducing costs and increasing safety of farm workers handling milk.

    Hobby farmers milking one or two cows or large commercial dairy farms could implement milk acidification without having to invest in large equipment.

    “When we started this project, we were carefully thinking about not just deactivating the virus but developing a method that could be affordable, accessible and sustainable for farmers to use,” he said.

    Some U.S. dairy farms already practice milk acidification. Lowering milk pH to a level unsuitable for bacterial growth can kill bad bugs and prevent contamination without causing health issues in calves.

    “We believe acidification is a novel and effective way to contain the spread of H5N1 on dairy farms and help protect livestock, pets and people,” Periera said.

    Other authors of the study include Beate Crossley and Daniel Rejmanek from the California Animal Health and Food Safety Lab at UC Davis, along with Craig Miramontes and Rodrigo Gallardo with the Department of Population Health and Reproduction at the UC Davis School of Veterinary Medicine.

    The California Department of Food and Agriculture and the United States Department of Agriculture funded the research. Media Resources


    Media Contacts:https://www.ucdavis.edu/news/killing...pasteurization

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