Image courtesy of Péter Kövesi via Pexels.
On March 25, 2024, the USDA, CDC, and FDA confirmed that a new strain of avian influenza virus type A (H5N1) had been found in dairy cows. While bird flu has long circulated among poultry and occasionally infected mammals, its emergence in dairy cattle marks a surprising shift—one with potential economic and public health implications.
H5N1 is classified as highly pathogenic in poultry, meaning it causes severe illness and high mortality in these domesticated birds; the virus can wipe out entire flocks of chickens in a matter of days, with a mortality rate of up to ninety percent. Cows and birds often share close quarters, which cultivates an environment for the disease to jump from species to species. Researchers suspect that H5N1 is spreading through milk and milking processes, though investigations, as of March 2025, are ongoing to determine the full scope of transmission risks.
H5N1 is a zoonotic disease, meaning it can jump from animals to humans through direct contact, inhalation, contaminated surfaces, or insect vectors. While no cases of human-to-human transmission have been reported, the CDC has documented sporadic infections in people. Globally, nearly half of those who have been infected have died. In response to the outbreak, federal and state agencies have imposed restrictions and testing policies to limit the spread of H5N1 and better understand its transmission dynamics to prevent further infections.