Aug. 18 (UPI) -- All respiratory viruses are airborne, including influenza and the new coronavirus that causes COVID-19 -- but the how remains a point of contention among scientists.
While most researchers have focused on how viral particles become airborne via coughing, sneezing and breathing, research published Tuesday in the journal Nature Communications suggests exhalation isn't a prerequisite for floating viral particles.
In the study, researchers at the University of California, Davis, found bits of virus can be carried through the air by flecks of dust.
"Right now, most research implicitly assumes that the only source of virus-laden aerosols is respiratory droplets -- from coughing, speaking, et cetera," lead study author William Ristenpart told UPI in an email.
"Our work clearly establishes that non-respiratory sources, such as a contaminated Kleenex, can generate virus-laden aerosol particles," said Ristenpart, a professor of chemical engineering at UC Davis.
Scientists started their work by painting influenza viral particles onto the fur of immune, uninfected guinea pigs. Particle counters helped scientists monitor the movement of viral particles through the cages.
Their data showed these virus particles are readily shed and can cling to tiny pieces of fur and hay, take flight and move through the air. Particle counters registered as many 1,000 airborne particles per second emanating from contaminated guinea pigs as they moved throughout their cages.
The experiment confirmed nearby guinea pigs susceptible to the virus could become infected, suggesting exhalation isn't necessary for the spread of influenza.
In a followup test, scientists deposited influenza particles onto a tissue and then crumpled it in front of a particle counter. The experiment generated 900 particles per second.
While researchers can't confirm whether or not humans regularly transmit viruses via dust, the new research suggests it's a possible.
"It is well established that infected humans also contaminate their environment with influenza and [COVID-19]," Ristenpart said. "It's also well established that humans generate micron-scale aerosol particulates from their skin and clothing. It remains to be established whether viral pathogens are transmitted between humans this way."
When Ristenpart and his colleagues compared the number viral particles shed by euthanized, or dead, guinea pigs and anesthetized, but still breathing, guinea pigs, they found the numbers were surprisingly similar.
"This result raises the possibility that influenza transmission between guinea pigs, and possibly in other animal models, is primarily due to aerosolized fomites rather than respiratory droplets as implicitly assumed," Ristenpart said.
"If so, a great deal of prior work will need to be reassessed in terms of the interpretation of the specific results and how to relate the findings to human transmission," he said.