Non-respiratory particles emitted by guinea pigs in airborne disease transmission experiments

Abstract

Animal models are often used to assess the airborne transmissibility of various pathogens, which are typically assumed to be carried by expiratory droplets emitted directly from the respiratory tract of the infected animal. We recently established that influenza virus is also transmissible via “aerosolized fomites,” micron-scale dust particulates released from virus-contaminated surfaces (Asadi et al. in Nat Commun 11(1):4062, 2020). Here we expand on this observation, by counting and characterizing the particles emitted from guinea pig cages using an Aerodynamic Particle Sizer (APS) and an Interferometric Mie Imaging (IMI) system. Of over 9000 airborne particles emitted from guinea pig cages and directly imaged with IMI, none had an interference pattern indicative of a liquid droplet. Separate measurements of the particle count using the APS indicate that particle concentrations spike upwards immediately following animal motion, then decay exponentially with a time constant commensurate with the air exchange rate in the cage. Taken together, the results presented here raise the possibility that a non-negligible fraction of airborne influenza transmission events between guinea pigs occurs via aerosolized fomites rather than respiratory droplets, though the relative frequencies of these two routes have yet to be definitively determined.

Influence of Human Activities and Occupancy on the Emission of Indoor Particles from Respiratory and Nonrespiratory Sources

“…Our current findings (i.e. skin-shedding and clothing being a dominant source of particles from humans), combined with the findings from previous studies on the presence and resuspension of pathogens from clothing and skin surfaces, ,,− suggest that non-respiratory sources could also play a role in the airborne transmission of pathogens, in addition to respiratory aerosol emissions. However, given the lack of measurements of any pathogens in our study, this is only a hypothesis which warrants that more systematic studies are needed to characterize the non-respiratory fraction of aerosols emitted from humans to investigate if and to what extent they can contribute to the spread of infectious diseases.…”

“…Our chamber experiments further show that most of the particles directly emitted by humans are nonrespiratory in origin. Numerous studies have reported the presence, − as well as the resuspension of pathogens (bacterial and viral) from clothing. − Asadi et al , demonstrated that aerosolized fomites produced from contaminated body surfaces contribute to airborne transmission of influenza in guinea pigs. Our current findings (i.e.…”

“…To date, there have been several studies quantifying the particle emission rates (PER), both from respiratory and nonrespiratory sources. For example, studies have been conducted to measure respiratory particle emissions during various human activities in clean environmental chambers, although without distinguishing between inert and infectious aerosols. − In separate investigations, particle emissions from nonrespiratory sources such as clothing, , skin-shedding, resuspension from flooring, , and total particle emissions associated with human activities (i.e., a combination of both respiratory and nonrespiratory sources), have also been quantified. − Recent studies have also reported airborne transmission of influenza in guinea pigs through the release of aerosolized fomites from contaminated body surfaces, , suggesting the role that nonrespiratory sources of particles from humans could play in the transmission of infectious diseases. Based on a microenvironmental exposure modeling framework, Kvasnicka et al reported that SARS-CoV-2 transmission through resuspension from clothing is theoretically feasible, although the chances are 2 orders of magnitude lower than primary inhalation exposure to respiratory aerosols.…”

Host and viral determinants of airborne transmission of SARS-CoV-2 in the Syrian hamster

“…We report a rise in <0.53 μm particles and a drop in particles in the 1-10 μm range after infection. One of the caveats of these measurements in small animals is that detected particles may come from aerosolized fomites, and residual dust generated by movement [33]. In our system, we did not detect any particles originating from dead animals or the environment, but we also saw a noticeable reduction of particles across sizes when movement was minimal, or animals were deeply asleep.…”

Modeling Clothing as a Vector for Transporting Airborne Particles and Pathogens across Indoor Microenvironments

“…For instance, clothing accumulated inhalable and respirable particles (≤10 μm) from indoor air in experiments, which were then resuspended during typical human activities. − Such resuspension may have caused airborne SARS-CoV-2 genetic material (RNA) in protective-apparel removal rooms in a hospital environment . Resuspension (or “aerosolized fomite”) is also a suspected cause of the transmission of SARS-CoV-2 and influenza virus in controlled animal studies. − However, the potential for clothing to transmit SARS-CoV-2 between humans remains an open question …”