Scientists Crack Why Bird Flu Attacks Cow Udders Instead of Lungs
University of Pittsburgh researchers discovered H5N1 targets mammary tissue in dairy cows due to concentrated glycan receptors — a finding that could predict future outbreaks.
Summary
Researchers at the University of Pittsburgh have solved a key mystery from the 2024 H5N1 bird flu outbreak in U.S. dairy cattle. Rather than causing respiratory disease as expected, the virus attacked cows' udders, puzzling veterinarians. The new study, published in Science Advances, reveals that the specific sugar-based receptors H5N1 needs to infect cells are concentrated in mammary tissue, not the lungs, in cattle. This explains the unusual outbreak pattern and raises important public health considerations — infected cows shed large amounts of virus into milk, posing occupational risks for farm workers and dangers to pets fed raw milk. Pasteurization effectively destroys the virus. The findings could help scientists anticipate how H5N1 behaves if it jumps to new species.
Detailed Summary
When H5N1 bird flu began spreading through U.S. dairy herds in early 2024, it broke every expectation. Instead of attacking the respiratory system as influenza typically does in mammals, the virus caused severe necrotizing mastitis — a destructive inflammatory disease of the mammary glands — while largely sparing the lungs. Veterinarians initially searched for bacterial causes, unaware a novel viral host had emerged.
Researchers at the University of Pittsburgh School of Public Health, led by infectious disease chair Suresh Kuchipudi, partnered with Harvard glycomics expert Lauren Pepi to investigate the biological mechanism behind this unusual pattern. Using advanced glycomics technology, they mapped the fine-grained architecture of glycan receptors in bovine tissues. Influenza viruses attach to host cells via these sugar-based molecules in a lock-and-key fashion, and the team found that the specific receptors H5N1 prefers are concentrated in mammary tissue rather than in the nose, trachea, or lungs of cattle.
This discovery provides the first detailed biological explanation for why H5N1 behaved so differently in cows. Earlier studies had detected flu-related glycan receptors in bovine respiratory tissue, creating confusion about why respiratory disease wasn't predominating. The new analysis resolved that discrepancy by identifying which precise glycan structures the virus actually binds to most effectively.
From a public health standpoint, the findings carry important implications. Infected cows shed high concentrations of virus into their milk. This creates occupational hazards for farm workers and risks for pets given raw milk — prior research linked H5N1 to cat deaths via raw milk consumption. Critically, pasteurization effectively neutralizes the virus, reinforcing why unpasteurized dairy products should be avoided.
The broader value of this research lies in predictive power. Understanding receptor distribution across tissues and species gives scientists a framework to anticipate where H5N1 might strike next and in what form, enabling earlier detection and faster containment of future spillover events.
Key Findings
- H5N1 preferentially binds glycan receptors concentrated in bovine mammary tissue, not lungs, explaining udder infections.
- Infected dairy cows shed high levels of H5N1 virus into milk, raising occupational risk for farm workers.
- Pasteurization effectively destroys H5N1 in milk, making raw milk consumption a clear risk.
- Mapping glycan receptor distribution across species may help predict future H5N1 host-jumping behavior.
- Cats fed raw milk from infected cows have died, confirming cross-species transmission risk via dairy.
Methodology
This is a news summary of a peer-reviewed study published in Science Advances, a credible open-access journal from the AAAS. The research combines glycomics analysis with receptor mapping using advanced molecular technologies from University of Pittsburgh and Harvard Medical School. The article is a research summary rather than a primary data report, so full methodology details require review of the original publication.
Study Limitations
The article is a summarized news report and does not detail sample sizes, statistical methods, or the full scope of tissues analyzed in the original study. Findings are specific to dairy cattle and may not directly translate to human infection patterns. The study's predictive framework for future H5N1 host jumps remains theoretical and requires further validation across species.
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