H5N1 Bird Flu in the United States: Dairy Cattle Outbreak
In 2024, H5N1 spread through US dairy cattle herds for the first time in history — a development with significant pandemic preparedness implications.
The Unprecedented 2024 Dairy Cattle Outbreak
In March 2024, H5N1 influenza A was confirmed in dairy cattle in Texas — the first time in history this highly pathogenic virus had been found in cattle of any kind. The virus spread rapidly through cattle movement between farms (milking equipment, farm workers) rather than through wild bird contact alone.
By early 2025, H5N1 had been confirmed in over 900 dairy cattle herds across 15+ US states, spanning from Texas and Michigan to California — the epicenter of US dairy production. Millions of cattle were exposed. Poultry outbreaks (H5N1 in chickens and turkeys) continued simultaneously, with over 100 million birds culled since 2022.
Human Infections: Farm Workers at Risk
| Feature | 2024–25 US Cases |
| Human cases (confirmed) | Dozens (as of early 2025) |
| Exposure source | Infected cattle (majority); poultry |
| Most common symptom | Conjunctivitis (eye inflammation) |
| Severe respiratory cases | Rare; 1 death (immunocompromised) |
| Human-to-human transmission | NOT confirmed |
Raw Milk Warning
US Response Measures
- CDC: monitoring farm workers, antiviral stockpiling (oseltamivir), updated case guidance
- USDA: mandatory testing of cattle before interstate movement (April 2024), milk testing at pasteurization plants
- FDA: confirmed pasteurized milk is safe; warned against raw milk
- BARDA: authorized mRNA-1018 (Moderna) H5N1 vaccine for high-risk groups
- PPE recommendations: farm workers should wear gloves, goggles, N95 respirators when handling potentially infected animals
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Frequently Asked Questions
Yes. Pasteurization effectively kills H5N1 and all other known influenza viruses. FDA testing of commercially pasteurized milk has not found live infectious virus. Pasteurized milk from grocery stores is safe. Raw (unpasteurized) milk is not safe during this outbreak.
No human-to-human H5N1 transmission has been confirmed in the US outbreak as of 2025. All confirmed cases involved direct animal exposure. The risk of pandemic spread currently depends on whether the virus acquires mutations enabling efficient human-to-human transmission — which has not happened yet.
Farm workers with exposure to potentially infected cattle or poultry should: wear N95 respirators, goggles or face shields, gloves, and protective clothing. Report any respiratory illness or eye symptoms to a healthcare provider immediately and mention animal exposure history. Seek antiviral treatment (oseltamivir) without waiting for test confirmation if H5N1 is suspected.
Sources: CDC H5N1 case count; USDA APHIS H5N1 herd tracking; FDA raw milk guidance; NEJM H5N1 dairy outbreak characterization; Moderna mRNA-1018 authorization data.
Related: H5N1 overview · H5N1 dairy archive