Fig. 1.

Virulence and transmissibility of clade 2.3.4.4b mink H5N1 viruses in ferrets. Ferrets (three per group) were inoculated with 10⁶ plaque-forming units (PFU) of A/mink/Spain/22VIR12774-13_3869-2/2022 (H5N1, mink 3869-2), A/mink/Spain/22VIR12774-14_3869-3/2022 (H5N1, mink 3869-3), or A/Isumi/UT-KK001-01/2018 (H1N1, H1N1pdm) virus. One day later, naïve animals were placed into cages that allowed air flow, but no direct contact between the infected and exposed animals. Nasal swab samples were collected at the indicated timepoints and virus titers were determined by performing plaque assays with MDCK cells. ∗Ferrets met euthanasia criteria. ^†Ferrets were euthanized on Day 10 post-infection or Day 9 post-exposure, respectively, because the virus infection had cleared. The dotted line indicates the detection limit (1.0 log₁₀ PFU/ml).