Figure 4.

Transmissibility of A/Chile/25945/2023 A(H5N1) virus in ferrets. Six ferrets inoculated with 6.0 log₁₀ EID₅₀ of virus were used to test transmission in the presence of direct contact (A) or via respiratory droplets (B). Nasal wash samples were collected from both the inoculated (left side of each panel) and contact ferrets (right side of each panel) every other day post-inoculation or post-contact for titration in eggs. Bars represent individual ferrets. * Indicates the day when the animal was euthanized due to severe clinical signs of infection; viral titres in tissues for euthanized ferrets are shown in Figure 3B. Air samples were collected from each of the six inoculated ferrets for 1 h on days 1–3 post-inoculation and evaluated for the presence of viral RNA copies/hour of collection at 3.5 L/min. Grey circles represent viral RNA detected in particles of >4 µm, navy blue squares represent viral RNA detected in particles of <4 µm, green triangles represent viral RNA detected in nasal washes collected after aerosol sampling and are expressed as RNA copies/ml (C). Three additional inoculated ferrets were used to test for fomite transmission. The transmission experiment was conducted for 3 days, after which the inoculated ferrets were euthanized to test for virus tissue distribution (Figure 3A). Prior to swapping cages between inoculated and naïve ferret pairs, duplicate cage swabs were collected and subsequently assessed for the presence of infectious virus and viral RNA (E). The limit of detection was 1.5 log₁₀ EID₅₀ /ml (dashed line) and 210 RNA copies/hour of air collection at 3.5 L/min.