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Bird Flu's Challenge for Milk Producers

Dairy Cows being milked in a modern milking parlor

For the past two weeks, numerous publications have examined the findings of a study published in the New England Journal of Medicine that found remnants of highly pathogenic avian influenza in pasteurized milk. Should producers and consumers worry that pasteurization may not eliminate all traces of the virus?  

The early thinking (hope?) was that the pasteurization process would kill the virus in the milk, so there would be no threat to consumers. Mainstream media and agricultural-focused publications relayed that information.  

Since then, scientists at the National Institutes of Health released the results of a study that they co-authored on bird flu in pasteurized milk. They conducted experiments at the agency’s lab.

Researchers added high levels of the bird flu virus into raw milk. They then put the milk through two different pasteurization processes to study the effects.

  • 1st method: Heated milk to 63 degrees Celsius (145 degrees Fahrenheit) for 30 minutes.

  • 2nd method: Heated milk to 72 degrees Celsius (161 degrees Fahrenheit) for 15 seconds.

The International Dairy Foods Association considers the pasteurization process of briefly heating milk to 72 degrees Celsius for 15 seconds to be the most common of the two in the United States.

Temperature and Pasteurization type chart
Milk pasteurization process options. Image courtesy: International Dairy Foods Association.

If you want to see how scientists described their experiment, check out this paragraph from their findings:

“We diluted HPAI A(H5N1) virus A/mountain lion/MT/1/2024 (clade; Global Initiative on Sharing All Influenza Data [GISAID] accession number, EPI_ISL_19083124) in raw (unpasteurized) cow’s milk to 106 50% tissue-culture infectious doses (TCID50) per milliliter of medium. We heat-treated the milk in a temperature-controlled heat block at 63°C and 72°C. We quantified infectious virus by means of end-point titration in Madin–Darby canine kidney cells, using 1:10 serial dilutions. HPAI A(H5N1) genome copies were quantified by quantitative reverse-transcriptase–polymerase-chain-reaction (qRT-PCR) assay.”

The final paragraph of the report – which is helpful for those of us who aren’t researchers – underscores the need for further study on this matter.

  • Researchers point out that they conducted their experiment in a lab and not in a dairy operation.

  • They say more research is needed for other dairy products.

  • They don’t know if raw milk from infected dairy cows has a different composition than the milk that they used.

  • They also don’t know if humans suffer adverse effects from consuming milk with remnants of bird flu.

Here is how they explain the need for additional research on bird flu’s impact on pasteurized milk:

“Our findings highlight the need for research on HPAI A(H5N1) virus in dairy production. Replication of these findings and extension to other dairy products is needed, including the study of milk from infected dairy cows with commercial pasteurization equipment, because treatment conditions can alter the effectiveness of heat inactivation.5 One limitation of our study is the use of raw-milk samples spiked with HPAI A(H5N1) virus, since raw milk from infected cows may have a different composition or may contain cell-associated virus that could have an effect on inactivation kinetics. Lastly, although gastrointestinal infections with HPAI A(H5N1) virus have been reported in several mammalian species,2 the dose dependence of the probability of human infection through ingestion of HPAI A(H5N1) virus in milk is unknown.”

RELATED: National Public Radio affiliate, WFYI in Indianapolis, breaks down the study that showed that bird flu could survive milk pasteurization. Listen to that here. 

Meanwhile, the USDA has confirmed that bird flu has spread to more dairy herds. At least a dozen states now have confirmed cases with more than five dozen additional dairy herd infections reported over the past month. See a map with the total number of confirmed dairy herds and the states impacted here. 


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