Background
In March 2024, the USDA confirmed the first case of highly pathogenic avian influenza (HPAI) spreading between dairy cattle herds in the United States. This followed reports from dairy producers of an unusual illness in their lactating cows over the preceding 2-3 months. Virus whole genome sequencing and modeling performed by USDA suggested a single spillover of HPAI H5N1, clade 2.3.4.4b, genotype B3.13 from wild birds into dairy cattle likely occurred between October 2023 and January 2024 (1). Since then, federal, state, and industry partners have collaborated to address the HPAI threat in dairy cattle, resulting in two federal orders and the implementation of the National Milk Testing Strategy (NMTS)