NY Academy of Sciences While the risk to the public remains low, the highly pathogenic avian influenza (HPAI) A(H5N1) is on the radar of those in sectors like livestock breeding, animal sciences and food production.
Recent observations on highly pathogenic avian influenza (HPAI) A(H5N1) have highlighted the virus’s transmission among dairy cattle in the United States. Key findings include ongoing detection and transmission of H5N1 among cattle, a second human case of H5N1 infection in a farmworker; mixed virus receptor distribution in mammary gland tissue of cattle, genetic evolution of H5N1 with onward transmission, evaluation of pasteurization effectiveness for virus inactivation, and a clinical description of HPAI H5N1 influenza A virus infection in a U.S. dairy farm worker.
Genomic and Epidemiologic Insights
In May 2024, investigators at the U.S. Department of Agriculture (USDA) reported genomic and epidemiologic data showing HPAI A(H5N1) spillover to, and transmission among, cattle. While prior data on Influenza A virus in cattle is scarce, the current geographic expansion of HPAI H5N1 among herds across multiple U.S. states demonstrates clade 2.3.4.4b’s affinity for cattle.
Reduced food intake, milk production, and shifting milk quality was first noted in January 2024, followed by detection of influenza A virus, specifically H5N1 clade 2.3.4.4b genotype B3.13, by the National Animal Health Laboratory Network and National Veterinary Services Laboratories. Subsequent analysis suggested movement of genotype B3.13 between dairy cattle farms and domestic poultry.
The study’s authors suggested a single spillover event from wild birds with limited cattle-to-cattle transmission around December 2023. Additional spillovers were identified from infected cattle to poultry and other nearby mammals, with the virus potentially shedding from infected cattle for 14-21 days. Genome sequencing indicated ongoing evolution, possibly linked to mammalian adaptation.