Fig. 1.

Ferret-to-ferret transmissibility is associated with the quantity and size of virus-laden particles in air released by the donor ferrets. Transmission of (A) CA04, (B) Rg-WH359, and (C) KS246 among ferrets via virus-laden particles that passed through the impactors with 50% collection efficiency at 9.9 µm, 5.3 µm, 2.5 µm, or 1 µm. Viral titers (log₁₀TCID₅₀/mL) detected in the nasal washes from recipient ferrets (detection limit at 1.789 log₁₀TCID₅₀/mL). For each impactor, the experiments were independently repeated three times for CA04 and Rg-WH359 (recipient, n = 6) and twice for KS246 (recipient, n = 4). (D) Viral titers detected in donor nasal washes after inoculation with CA04 (n = 24), Rg-WH359 (n = 24), or KS246 (n = 8) influenza viruses and overlaid with mean ± SD. (E) Temperature and (F) weight changes of donor ferrets after inoculation with CA04 (n = 22–24), Rg-WH359 (n = 20–24), or KS246 (n = 8) viruses and overlaid with mean ± SD. (G) APS was applied to determine size distribution (range, 0.52–20.53 µm) of total particles released in air by donor ferrets (n = 9, n = 10, and n = 4 for CA04, Rg-WH359, and KS246, respectively) at 2 dpi or by noninoculated ferrets (n = 9). (H) Quantity and size distribution of influenza virus-laden particles sampled from the donor chambers during the exposure period using the NIOSH bioaerosol sampler. The limit of linear range of quantification (476 M gene copies per cubic millimeter) is shown with the dotted line. Data from each exposure (n = 12, n = 10, and n = 4 for CA04, Rg-WH359, and KS246, respectively) are shown and overlaid with median and interquartile range. (I) Schematic representation of the transmission experiment with artificially generated aerosols. (J) Viral titers (log₁₀TCID₅₀/mL) detected in the nasal washes of recipients ferrets after exposure to nebulized CA04 aerosols that passed through the 1.0-µm impactor; the experiments were independently repeated three times. (K) Viral titers (log₁₀TCID₅₀/mL) detected in the nasal washes of recipients ferrets after exposing to nebulized Rg-WH359 aerosols that passed through the 1.0-µm impactor; the experiments were independently repeated three times. P values <0.05 from Dunn’s multiple comparisons after Kruskal–Wallis test are shown.