Extended Data Fig. 1: Experimental air-sampling set-up.

For the collection of air-samples, the BioSpot-VIVASTM Series 315 bioaerosol sampler (Aerosol Devices, USA) was directly connected to a ferret cage holding an individually housed ferret, via a 1.4 m long tubing. The BioSpot was operated with a flowrate of 15 L min-1 under the following conditions: conditioner: 5 °C; initiator: 45 °C; moderator: 18 °C; nozzle: 27 °C; sample holder: between 13-16 °C. No extra airflow was supplied to the ferret cage, in addition to the 15L min-1 applied by the BioSpot sampler. With a cage volume of 45 L (30 ×30 x 50 cm) and a flow rate of 900L h-1 (60 x 15L min-1), this results in 20 (900L h-1 / 45 L) air changes per hour. The ferret cage and BioSpot were housed in separate, interconnected, negatively pressurized class 3 isolators. This separation was necessary because the BioSpot generated excessive heat, which led to an increased ambient temperature within the isolator.