We do this experiment… in darkness.
On the left is a human infected with a respiratory disease (eg influenza A, SARS-CoV-2, coronavirus OC43) which is our transmission source. They are instructed to talk so as to produce virion-containing aerosols. Air is drawn into a mixing chamber, mixed to ensure an equal concentration of infectious aerosols, then channelled off through three identical tubes. The tubes are horizontal to ensure equal settling of aerosols, and the 3 hamster areas need to be as identical as possible.
Tube 1 is the control. This shows the base level of infection at the distance and aerosol concentration.
Tube 2 imparts the same level of thermal energy as tube 3 via infrared heaters into the tube, to see how heat rise affects transmission rate.
Tube 3 exposes aerosols to artificial sunlight, this is the active part of the experiment and assesses how sunlight affects transmission rate.
The darkness filters are required to make sure the light exposure doesn’t modify hamster behaviour, and in doing so change transmission rates. They are installed in all three tubes to make the experiment setup identical. Air passes through unimpeded.
Experiment temperature, humidity, and time length is recorded.
The goal is to measure the proportion of infected hamsters in each hamster area.
Interpreting results:
No significant infections in any hamster areas. Modify experiment to improve transmission;
- Shorten tubes between hamster areas and infection source.
- Prolong length of time of experiment.
- Increase fan speed to increase air speed.
Almost all hamsters infected in all hamster areas. Modify experiment to reduce transmission;
- Shorten length of time of experiment.
- Reduce fan speed to reduce air speed.
Approximately equal number of infections in each hamster area. Neither temperature nor light exposure influences respiratory disease transmission rates.
Proportion infected hamsters in 1 < proportion of infected hamsters in 2 ~= proportion of infected hamsters in 3. Temperature, not light, is the bigger driver in transmissibility. Sunlight becomes heat in the tube, so thermally tube 2 and tube 3 are identical.
Proportion infected hamsters in 1 < proportion of infected hamsters in 2 << proportion of infected hamsters in 3. Light is a bigger driver of airborne virus transmissibility than heat. This shows that light triggers and powers the transmission immune system, and we can begin to investigate this process.
But what if it’s not the interaction with light with the virions and mucus, but instead it’s the interaction with light with the virions that cause them to lose transmissibility? So let’s design a second experiment to investigate this.