H5N1 highly pathogenic avian influenza poses a serious threat to both animal and human health. Since 2021, a novel H5N1 virus has caused thousands of outbreaks among poultry and wild birds across multiple countries. In March 2024, H5N1 virus was first reported in dairy cattle in the United States. As of June 2025, outbreaks have been reported on more than 1,070 dairy farms across 17 states, with a mortality rate of up to 10% in affected cattle. Moreover, 41 dairy farm workers were infected by the virus, highlighting a significant threat to the global dairy industry and public health. The H5N1 virus causes severe lesions in the mammary glands and contaminates milk, with H5N1 viral genes detected in 25% of retail milk samples in the U.S. However, as a typical respiratory pathogen, how does the H5N1 virus enter the mammary glands of dairy cows? A Chinese research team led by Professor Hualan Chen has solved this mystery, and they also provide a strategy on how to control the disease in cattle.
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