Spillover of highly pathogenic avian influenza H5N1 virus to dairy cattle

The highly pathogenic avian influenza (HPAI) H5N1 virus has recently been reported to spill over into dairy cattle in the United States, affecting herds across multiple states. Since January 2022, this virus has led to significant mortality among domestic and wild birds. Affected dairy cows exhibited clinical symptoms such as reduced feed intake, respiratory distress, altered fecal consistency, and decreased milk production, with the presence of abnormal milk. The virus and its RNA were consistently found in the milk of these cows. Research utilizing immunohistochemistry and in situ hybridization revealed that the virus specifically targets the epithelial cells of the mammary gland's alveoli. Whole genome sequencing indicated that the virus has been transmitted between various species, including birds, domestic cats, and raccoons, on the same farms. Notably, epidemiological data showed effective transmission from cow to cow, particularly after healthy cows from an infected farm were moved to a different location. This situation highlights the virus's ability to cross species barriers and raises concerns about its potential impact on livestock health and food safety. The findings underscore the importance of monitoring and controlling HPAI H5N1 to prevent further spillover events and protect both animal and public health.