• Recent research is shedding new light on virus transmission.
• The study, focussing on the influenza virus, shows the virus can “stick” to non-respiratory particles, such as dust.
• These results have major implications for the Covid-19 pandemic.

Influenza (flu) viruses spread among humans in various ways, such as via exhaled droplets or secondary objects like door handles and used tissues. These secondary objects are known as fomites.

A new study, however, provides new evidence of a mode of transmission seldom considered in influenza: airborne transmission on microscopic particles, called “aerosolised fomites”.

The research, by the University of California, Davis (UC Davis) and the Icahn School of Medicine at Mount Sinai, also has obvious implications for coronavirus transmission.

The findings were published in Nature Communications.

Airborne viruses can ‘catch a ride’ on fibres

For the new study, UC Davis engineering graduate students teamed up with virologists at Mount Sinai to investigate whether tiny, non-respiratory particles, or aerosolised fomites, could carry the influenza virus between guinea pigs.

The team used an automated particle sizer to count airborne particles and found that uninfected guinea pigs gave off spikes of up to 1 000 particles per second as they moved around the cage. Particles given off by the animals’ breathing, however, were at a constant, much lower rate.

The influenza virus was then painted on the fur of immune guinea pigs. Findings indicated that they could transmit the virus through the air to other guinea pigs. This means that airborne viruses may not have to come directly from the respiratory tract to be infectious.

The researchers also tested whether microscopic fibres from an inanimate object could carry infectious viruses. To do this, they treated paper facial tissues with influenza virus and let them dry out. Following this, they crumpled the tissues in front of the automated particle sizer.

The tissues were found to release up to 900 particles per second in a size range that could be inhaled, the study results show. More than this, the particles released from the virus-contaminated paper tissues were able to infect cells.

‘Dust transmission opens up new areas of investigation’

“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 Professor William Ristenpart of the UC Davis Department of Chemical Engineering, who was involved in the study.

“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.” 

READ: Covid-19: Practical guidance on disinfecting

READ: Importance of wearing masks during Covid-19 pandemic – amid concerns over aerosol spread

^{Image: Caleb Betteridge}

Compiled by Zakiyah Ebrahim