Conventional wisdom states that airborne viruses like influenza and Covid-19 can only be transmitted by respiratory droplets that are released when an infected person coughs or sneezes, yet new research may have just shattered that assumption. According to a study in the journal Nature Communications, flu-like viruses can also be carried through the air by dust, fibers, and other tiny particles that are not of a respiratory origin.

It is well known that secondary objects like door handles or table surfaces can also spread viruses if infected droplets land on them. Known as fomites, these secondary transmitters come in all shapes and sizes, yet the study authors wanted to know if microscopic particles in the air – known as aerosolized fomites – could also carry influenza viruses.

To investigate, they first used an automated particle sizer to measure how many airborne particles are kicked up by guinea pigs as they move around their cages. Results showed that the rodents tended to whip up clouds of about 1,000 minuscule particles with each major movement.

Next, the researchers coated the fur of immune guinea pigs with an influenza virus and found that this virus remained viable for at least four days. As the animals moved around during this period, the virus on their fur became aerosolized and spread to another cage that housed 12 non-immune guinea pigs, three of which became infected.

In other words, the virus was carried by aerosolized fomites from one cage to another, proving that influenza can be transmitted by tiny particles that do not originate in the respiratory tract of an infected individual.

"It's really shocking to most virologists and epidemiologists that airborne dust, rather than expiratory droplets, can carry influenza virus capable of infecting animals," said study author Professor William Ristenpart, from the UC Davis Department of Chemical Engineering, 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."

To investigate further, the researchers treated paper tissues with influenza, before letting them dry out for about 30 to 45 minutes. They then crumpled the dried tissues using their hands and found that this released around 900 aerosolized fomites per second.

These particles were then collected and used to infect cells in a petri dish, indicating that tiny fibers of dried tissue paper can also successfully transmit influenza viruses.

At present, there is much debate within the scientific community as to how Covid-19 is spread, with the World Health Organization (WHO) originally claiming that the virus could only be transmitted via direct contact with respiratory droplets. However, many scientists have argued that these droplets can become aerosolized and linger in the air, which means that people can catch the virus without coming into contact with an infected individual.

Yet this latest study takes this hypothesis a step further, suggesting that viruses can even attach to other airborne particles such as dust, which then transmit these pathogens as they travel through the air.