OFFLU Guidelines for High Pathogenicity Avian Influenza Virus Risk Mitigation in Cattle

High pathogenicity avian influenza viruses (HPAIVs) of the A(H5) Goose/Guangdong (Gs/Gd) lineage1 continue to pose. Previously largely restricted to avian hosts, these viruses have recently been involved in numerous interspecies transmission events affecting an expanding range. In early 2024, the first confirmed transmission of A(H5N1) virus to dairy cattle in the United States (US) was reported, involving clade 2.3.4.4b, US genotype (as defined by the ´GenoFlu´ B3.13. Since then, cattle have shown their capacity to sustain the circulation of the B3.13 virus lineage, and the detection of at least two additional US genotype D1.1 viruses in dairy herds in early 2025 suggests multiple independent interspecies transmission events.Experimental infections further confirm cattle´s susceptibility to other A(H5N1). As of September 2025, sustained spread in cattle appears geographically limited to the US. However, the repeated occurrence of these viruses in an atypical host raises urgent concerns about zoonotic risk, animal health, and the potential for similar incursions in other regions and species. Given its animal and public health impact, HPAIV in cattle meets the WOAH Terrestrial Code definition of an "emerging disease," requiring Member Countries to notify its occurrence, and underscores the need for timely,evidence-based risk mitigation strategies.