H5N1 clade 2.3.4.4b dynamics in experimentally infected calves and cows

In March 2024, highly pathogenic avian influenza virus (HPAIV) clade 2.3.4.4b H5N1 infections were reported in dairy cows in Texas, USA1. Rapid dissemination to more than 380 farms in 14 states followed2. Here we provide results of two independent clade 2.3.4.4b experimental infection studies evaluating the oronasal susceptibility to and transmission of a US H5N1 bovine isolate, genotype B3.13 (H5N1 B3.13), in calves, and the susceptibility of lactating cows following direct mammary gland inoculation of either H5N1 B3.13 or a current EU H5N1 wild bird isolate, genotype euDG (H5N1 euDG). Inoculation of the calves resulted in moderate nasal replication and shedding with no severe clinical signs or transmission…