A study indicates that influenza viruses can spread through the air not only in droplets — emitted by a person who has the virus when they speak, cough, or sneeze — but also on particles of microscopic dust.
Seasonal flu outbreaks are each year responsible for the deaths of hundreds of thousands of people all over the world. Millions can lose their lives in a pandemic, such as the Spanish flu pandemic of 1918.
To minimize transmission, scientists need to understand precisely how influenza viruses spread from one person to another.
Scientists also concluded that the droplets formed when a person with the virus breathes, speaks, coughs or sneezes are primarily responsible for the transmission of viruses through the air.
Yet a recent research indicates that dust, fibers and other microscopic particles may also spread influenza viruses through the air, with far-reaching effects to avoid and monitor outbreaks.
“It is really shocking for most virologists and epidemiologists that airborne dust may carry influenza virus capable of infecting animals rather than expiratory droplets,” says Professor William Ristenpart of the Chemical Engineering Department at the University of California Davis (UC Davis).
Prof. Ristenpart, along with scientists at UC Davis and the Icahn School of Medicine at Mount Sinai, NY, is one of the writers of this new research . The results appear in the journal Nature Communications.
“The implicit assumption is that airborne transmission is always due to breathable droplets emitted by coughing , sneezing, or talking,” he adds.
“Dust transmission opens up entirely new areas of investigation and has profound implications for how we interpret laboratory experiments, as well as epidemiological outbreak investigations.”
Through handling infected items such as doorknobs, toys, towels, and used tissues, people may contract viruses. Scientists refer to the infected artifacts as fomites. The researchers suggest that viruses can also be borne by aerosolized fomites, or infected dust particles.
Experiments showed that the influenza virus remained viable on materials like paper tissues and on the bodies of guinea pigs for long enough to become airborne on particles of dust. Such particles could then transfer the infection to new hosts, they showed.
During their studies they found that the influenza virus remained active for long enough on products such as paper tissues and guinea pig bodies to become airborne on dust particles. Such particles could then transfer the infection to new hosts, they showed.
Bursts of particles
First, to sample the air from a cage holding a guinea pig, the scientists used a tool called an aerodynamic particle sizer.
The system revealed that the animal produced airborne particles ranging in size from 0.3 to 20 micrometers (or one thousandths of a millimeter) in bursts of about 1,000 particles per second as it moved.
Healthy anesthetized animals exhaled only 0.10 to 0.18 particles per second and influenza-induced anesthetized animals produced 0.5 particles per second.
This indicated that dust accounted for the vast majority of particulate matter released into the air, rather than respiratory droplets, when the animals were involved.
The researchers infected guinea pigs with an influenza strain to check if such particles were likely to become contaminated with the virus. Two days later, swabs from their hair, head, paws, and cages were all developing viable viruses.
The researchers then investigated whether fomites aerosolized from one animal could infect another. To do so, they were using a paintbrush to add a solution of flu virus particles to the bodies of guinea pigs.
Scientists had previously infected these animals with this strain of flu, which was important, and they were resistant to reinfection. This meant that they did not cough out droplets laden with viruses.
When these cages were placed near those containing guinea pigs which were still vulnerable to the virus, 3 out of 12 of these animals acquired the infection.
“So we conclude that airborne particulate matter from a non-breathing source can transmit influenza virus to a susceptible host through the air,” the researchers write.
Paper tissues
Throughout their final experiment , the researchers explored whether the dust could carry viable virus particles from an inanimate source, namely a contaminated paper tissue.
The scientists applied a virus solution to the tissues and allowed them to dry out within 30-45 minutes. We then crumpled, folded, and rubbed the tissues alongside the aerodynamic particle sizer, which registered about 900 particle release a second.
They noticed the particles, which were small enough for inhalation, contained a virus that could still infect cell cultures in the laboratory.
“These results show that dried influenza virus remains viable in the environment, on materials such as paper tissues and on the bodies of living animals, long enough to be aerosolized on non-respiratory dust particles that can transmit infection through the air to new mammalian hosts.”
– Sima Asadi, et al
The researchers stress that in order to validate their findings, scientists would need to carry out more work in humans and other animal models.
If true, the discovery could be relevant to other respiratory viral infections, including SARS-CoV-2, the virus that causes COVID-19.
Nccmed focused on a study that took place at hospitals during the outbreak of COVID-19 in China in April. It showed that the highest levels of airborne viral RNA were in rooms that eliminated personal protective equipment from the healthcare staff.
This suggests the removal of infected clothing may aerosolize the virus, the new study authors write.
“In light of our experiments, we conclude that the contribution of aerosolized fomites to respiratory virus transmission in both humans and animal models requires further scientific consideration and rigorous investigation.”
