DAVIS, Calif. — It is widely accepted that respiratory viruses, like influenza, can be efficiently spread from person to person through the air. Scientists believe that this happens primarily when an infected person coughs, sneezes, or breathes. A new study suggests that flu viruses can also travel through the air on dust, fibers, and other microscopic particles.
This finding could have wide implications for aerosol transmission of other respiratory viruses, including SARS-CoV-2, the viral agent that causes COVID-19.
In the study, which is published in Nature Communications, researchers from the University of California, Davis and the Icahn School of Medicine at Mt. Sinai looked at flu virus transmission in a guinea pig model. They used an automated particle sizer to measure the airborne particles given off by the guinea pigs under various conditions.
How contaminated dust could transmit viruses
Researchers say that guinea pigs can produce spikes of up to 1,000 airborne particles per second as they move around in their cage. The authors report that these particles are comparable in size to those produced by human breath.
When the guinea pigs were anesthetized, and therefore not moving, the researchers found orders of magnitude fewer particles being produced. From this result, the authors conclude that a large proportion of the aerosolized particles produced by guinea pigs are from dust kicked up by the animals as they move around, rather than from the respiratory tract.
“Given that environmental dust comprised such a large fraction of the total airborne particulates emitted by experimental guinea pigs, we hypothesized that, if these airborne environmental dust particulates were to become contaminated with influenza virus, they could serve as vehicles on which influenza virus might transmit through the air,” the authors write in the study.
The authors coined the term, “aerosolized fomites,” to refer to these virus-contaminated dust particles.
Flu virus emitted by crumpled paper towels
Next, the group looked at whether influenza virus could be transmitted between guinea pigs on aerosolized fomites. To do this, they painted influenza virus onto the bodies of guinea pigs that were already immune to the virus, and paired them with guinea pigs that were still susceptible to infection. Viral transmission did occur between a subset of the animals in the study.
Finally, the scientists looked at the possibility that aerosolized fomites could originate from an inanimate object. They soaked various commercially available paper tissues and towels in liquid containing the flu virus and let them dry. They then crumpled, folded, and rubbed the tissues and towels to generate aerosolized fomites.
The study finds that tissues and towels release up to 900 particles per second. The sizes of the particles are comparable to the particles generated by guinea pigs moving in their cages.
‘Really shocking’ discovery ‘has profound implications’
The group reports that dried influenza virus can remain viable on the contaminated tissues and towels. After collecting the particles that had been released into the air from the crumpled tissues, the scientists were able to cultivate infectious flu virus in cell culture.
“It’s really shocking to most virologists and epidemiologists that airborne dust, rather than expiratory droplets, can carry influenza virus capable of infecting animals,” says William Ristenpart, one of the lead authors of the study, in a statement. “The implicit assumption is always that airborne transmission occurs because of respiratory droplets emitted by coughing, sneezing, or talking. Transmission via dust opens up whole new areas of investigation and has profound implications for how we interpret laboratory experiments as well as epidemiological investigations of outbreaks.”