One study suggests that flu viruses can spread through the air, not only in droplets – which a person who carries the virus releases when they talk, cough or sneeze – but also on microscopic dust particles.
Seasonal flu outbreaks are responsible for the deaths of hundreds of thousands of people each year. In a pandemic, like the Spanish flu pandemic of 1918, millions could lose their lives.
To reduce transmission, scientists need to understand exactly how influenza viruses spread from person to person.
Experts have assumed that the drops produced when a person with the virus breathes, speaks, coughs, or sneezes is solely responsible for the transmission of the viruses into the air.
But a new study suggests that dust, fibers, and other microscopic particles can also transmit flu viruses through the air, with far-reaching implications for preventing and controlling outbreaks.
“It’s really shocking to most virologists and epidemiologists that dust with air, instead of exhaling droplets, can affect animal feedings that can infect animals,” says Professor William Ristenpart of the Department of Chemical Engineering at the University of California Davis (UC Davis).
Professor Ristenpart is one of the authors of the new study, along with scientists at UC Davis and the Icahn School of Medicine at Mount Sinai, NY. The findings appear in the journal Nature communication.
“The implicit assumption is always that the transmission takes place through the air due to respiratory droplets emitted by coughing, sneezing or talking,” he adds.
“Substance transmission opens up entirely new areas of research and has profound implications for how we interpret laboratory experiments, such as epidemiological studies of outbreaks.”
People can contract viruses by touching infected objects, such as doorknobs, toys, towels and used tissue. Scientists call these contaminated objects fomites. The researchers believe that aerosolized fomites, like contaminated dust particles, can also carry viruses.
Experiments found that the influenza virus remained viable on materials such as paper tissues and on guinea pig bodies long enough to become airborne on dust particles. They showed that these particles could then transmit the infection to new hosts.
In their experiments, they found that the flu virus remained viable on materials such as paper tissues and the bodies of guinea pigs long enough to become airborne on dust particles. They showed that these particles could then transmit the infection to new hosts.
First, the scientists used a device called an aerodynamic particle sizer to extract air from a cage containing a guinea pig.
The device found that the animal generated airborne particles in sizes ranging from 0.3 to 20 micrometers (as a thousandth of a millimeter) in bursts of about 1,000 particles per second as it moved.
Healthy anesthetized animals escaped only 0.10 to 0.18 particles per second, and anesthetized animals with influenza generated 0.5 particles per second.
This suggested that dust, rather than as respiratory droplets, accounted for the vast majority of the particles released into the air while the animals were active.
To test whether these particles were likely infected with the virus, the researchers infected guinea pigs with a strain of influenza. Two days later, swabs from her fur, ears, legs and cage all delivered viable virus.
Next, the researchers examined whether aerosolized fomites from one animal could infect another. To do this, they applied a solution of flu virus particles to the bodies of guinea pigs with a brush.
Of crucial importance, scientists had previously infected these animals with this influenza strain, so that they were immune to reinfection. This means they would not exhale virus-laden drops.
When researchers placed these cages near those containing marsupials that were still susceptible to the virus, 3 out of 12 of these animals developed the infection.
“Thus, we conclude that particulate matter with air from a non-respiratory source can transmit an influenza virus through the air to a susceptible host,” the researchers write.
In their latest experiment, the researchers investigated whether the substance from a living source, namely an infected paper tissue, could carry viable virus particles.
The scientists applied a solution of the virus to the tissue and allowed it to dry for 30-45 minutes. They shrink, fold and rub the tissues next to the aerodynamic particle sizer, which record the release of about 900 particles per second.
They found that the particles, which were small enough for inhalation, carried in virus that was still able to infect cell cultures in the lab.
These results show that dry flu virus remains viable in the environment, on materials such as paper tissues and on the bodies of living animals, long enough to aerosolize on non-respiratory dust particles that can transmit infection through the air to new ones. mammal hosts. ”
– Sima Asadi, and others
The researchers stress that scientists need to conduct further research into humans and other animal models to confirm their results.
If confirmed, scientists could apply the discovery to other viral respiratory infections, including SARS-CoV-2, the virus that causes COVID-19.
In April, Medical news today reported on a study that took place in hospitals during the COVID-19 outbreak in China. It found that the highest levels of viral RNA were in the air in rooms where health care workers removed personal protective equipment.
This suggests that removal of contaminated clothing would aerosolize the virus, write the authors of the new study.
“In light of our experiments, we conclude that the contribution of aerosolized fomites to transmission of respiratory viruses in both human and animal models requires further scientific consideration and rigorous research.”
