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U.S. Department of Health and Human Services
NATIONAL INSTITUTES OF HEALTH NIH News
National Institute of Allergy and Infectious Diseases (NIAID) <https://www.niaid.nih.gov/>
For Immediate Release: Friday, March 1, 2024
CONTACT: NIAID News & Science Writing Branch,(301) 402-1663, <email:niaidnews@xxxxxxxxxxxxx>
MEDIA AVAILABILITY
HIGH H5N1 INFLUENZA LEVELS FOUND IN MICE GIVEN RAW MILK FROM INFECTED DAIRY COWS
Mice administered raw milk samples from dairy cows infected with H5N1 influenza experienced high virus levels in their respiratory organs and lower virus levels in other vital organs
WHAT:
Mice administered raw milk samples from dairy cows infected with H5N1 influenza experienced
high virus levels in their respiratory organs and lower virus levels in other vital organs, according
to findings published in the New England Journal of Medicine. The results suggest that
consumption of raw milk by animals poses a risk for H5N1 infection and raises questions about
its potential risk in humans.
Since 2003, H5N1 influenza viruses have circulated in 23 countries, primarily affecting wild
birds and poultry with about 900 human cases, primarily among people who have had close
contact with infected birds. In the past few years, however, a highly pathogenic avian influenza
virus called HPAI H5N1 has spread to infect more than 50 animal species, and in late March, the
United States reported a viral outbreak among dairy cows in Texas. To date, 52 cattle herds
across nine states have been affected, with two human infections detected in farm workers with
conjunctivitis. Although the virus has so far shown no genetic evidence of acquiring the ability to
spread from person-to-person, public health officials are closely monitoring the dairy cow
situation as part of overarching pandemic preparedness efforts.
To assess the risk of H5N1 infection by consuming raw milk, researchers from the University of
Wisconsin-Madison and Texas A&M Veterinary Medical Diagnostic Laboratory fed droplets of
raw milk from infected dairy cattle to five mice. The animals demonstrated signs of illness,
including lethargy, on day one and were euthanized on day four to determine organ virus levels.
The researchers discovered high levels of virus in the animals’ nasal passages, trachea and lungs
and moderate-to-low virus levels in other organs, consistent with H5N1 infections found in other
mammals.
In addition to the mice studies, the researchers also tested to determine which temperatures and
time intervals inactivate H5N1 virus in raw milk from dairy cows. Four milk samples with
confirmed high H5N1 levels were tested at 63 degrees Celsius (145.4 degrees Fahrenheit) for 5,
10, 20 and 30 minutes, or at 72 degrees Celsius (161.6 degrees Fahrenheit) for 5, 10, 15, 20
and/or 30 seconds. Each of the time intervals at 63℃ successfully killed the virus. At 72℃, virus
levels were diminished but not completely inactivated after 15 and 20 seconds. The authors
emphasize, however, that their laboratory study was not identical to large-scale industrial
pasteurization of raw milk and reflect experimental conditions that should be replicated with
direct measurement of infected milk in commercial pasteurization equipment.
In a separate experiment, the researchers stored raw milk infected with H5N1 at 4℃ (39.2
degrees Fahrenheit) for five weeks and found only a small decline in virus levels, suggesting that
the virus in raw milk may remain infectious when maintained at refrigerated temperatures.
To date, the U.S. Food and Drug Administration (FDA) concludes that the totality of evidence
continues to indicate that the commercial milk supply is safe. While laboratory benchtop studies
provide important, useful information, there are limitations that challenge inferences to real
world commercial processing and pasteurization. The FDA conducted an initial survey of 297
retail dairy products collected at retail locations in 17 states and represented products produced at
132 processing locations in 38 states. All of the samples were found to be negative for viable
virus. These results underscore the opportunity to conduct additional studies that closely
replicate real world conditions. FDA, in partnership with USDA, is conducting pasteurization
validation studies – including the use of a homogenizer and continuous flow pasteurizer.
Additional results will be made available as soon as they are available.
The National Institute of Allergy and Infectious Diseases, part of the National Institutes of
Health, funded the work of the University of Wisconsin-Madison researchers.
ARTICLE:
G Lizheng et al. Cow Milk Containing H5N1 Influenza Viruses—Heat Inactivation and
Infectivity in Mice. The New England Journal of Medicine DOI: 10.1056/NEJMc2405495
(2024).
WHO:
NIAID Director Jeanne Marrazzo, M.D., and Lauren Byrd-Leotis, Ph.D., with NIAID’s Division
of Microbiology and Infectious Diseases’ Viral Respiratory Diseases Section, are available to
discuss the findings.
NIAID conducts and supports research—at NIH, throughout the United States, and worldwide—
to study the causes of infectious and immune-mediated diseases, and to develop better means of
preventing, diagnosing and treating these illnesses.
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