Airflow between Animal Cages in Airborne Disease Transmission Experiments*

The airborne transmissibility of pathogens is often assessed using animal models, in which one animal is purposely inoculated and a naïve animal is placed downstream in a separate cage to see if transmission occurs. Although this paradigm has been widely adopted, little is known about what is actually carrying the pathogens from one animal cage to the other, and how the airflow conditions affect the transmission rate. Here we characterize the particles emitted from cages containing guinea pigs. We find that awake and mobile guinea pigs generate an average of 1000 particles/min, while anesthetized guinea pigs emit about 2 particles/min. The results suggest that expiratory particles account for less than 1% of all aerosol particles transmitted between cages.  Furthermore, we designed and tested an apparatus to test the effect of average airflow velocity on influenza transmission between guinea pigs, with preliminary results suggesting a weak dependence on velocity.