Airborne viruses can spread to dusty, non-respiratory particles

Influenza viruses can spread through the air to dust, fibers and other microscopic particles, according to new research from the University of California, Davis and the Icahn School of Medicine at Mt. Sinai. The findings, with implicit implications for coronavirus transmission as influenza, will be published August 18 in Nature communication.

“It’s very shocking to most virologists and epidemiologists that dust with air, instead of exhaling drops, can carry flu viruses that can infect animals,” said Professor William Ristenpart of the UC Davis Department of Chemical Engineering, who helped to lead the investigation. “The implicit assumption is always that airborne transmission occurs due to respiratory drops delayed by coughing, sneezing or chattering. Transmission through dust opens up entirely new areas of research and has profound implications for how we interpret laboratory experiments, such as epidemiological studies of outbreaks.”

Fomites and influenza virus

Influenza virus is thought to be spread by several different routes, including in droplets extracted from the respiratory tract or on secondary objects such as door handles or used tissue. These secondary objects are called fomites. However, not much is known about which routes are the most important. The response may be different for different strains of influenza virus than for other respiratory viruses, including coronaviruses such as SARS-CoV2.

In the new study, UC Davis engineering student Sima Asadi and Ristenpart collaborated with virologists led by Dr. Nicole Bouvier at Mt. Sinai to see if small, non-respiratory particles they call “aerosolized fomites” can carry influenza viruses between marsupials.

Using an automatic particle sensor to count the particles of air, they found that non-infected guinea pigs produce spikes of up to 1,000 particles per second as they move around the cage. Particles emitted by the animals’ breathing were at a constant, much lower rate.

Immune guinea pigs with flu virus painted on their fur could transmit the virus through the air to other, susceptible guinea pigs, showing that the virus did not have to come directly from the airways to be infectious.

Finally, the researchers are testing whether microscopic fibers of a living thing can carry infected viruses. They treated paper facial tissues with influenza virus, allowed them to dry out, and then crawled in front of the automated particle sizer. Crumples of the tissues released up to 900 particles per second in a wide range that could be inhaled, they found. They could also infect cells from these particles released from the virus-contaminated paper tissues.