Resistance of Aerosolized Bacterial Viruses to Relative Humidity and Temperature

Abstract

The use of aerosolized bacteriophages as surrogates for hazardous viruses might simplify and accelerate the discovery of links between viral components and their persistence in the airborne state under diverse environmental conditions. In this study, four structurally distinct lytic phages, MS2 (single-stranded RNA [ssRNA]), 6 (double-stranded RNA [dsRNA]), X174 (singlestranded DNA [ssDNA]), and PR772 (double-stranded DNA [dsDNA]), were nebulized into a rotating chamber and exposed to various levels of relative humidity (RH) and temperature as well as to germicidal UV radiation. The aerosolized viral particles were allowed to remain airborne for up to 14 h before being sampled for analysis by plaque assays and quantitative PCRs. Phages 6 and MS2 were the most resistant at low levels of relative humidity, while X174 was more resistant at 80% RH. Phage 6 lost its infectivity immediately after exposure to 30°C and 80% RH. The infectivity of all tested phages rapidly declined as a function of the exposure time to UVC radiation, phage MS2 being the most resistant. Taken altogether, our data indicate that these aerosolized phages behave differently under various environmental conditions and highlight the necessity of carefully selecting viral simulants in bioaerosol studies. Human populations are constantly exposed to viral particles, whether through direct or indirect contacts with an infected individual or through contaminated environments. Despite precautions, we remain at risk of exposure to infective viral particles, particularly through the airborne route. This mode of transmission is difficult to control in our everyday lives due to the ubiquitous nature of airborne particles, which may harbor infectious materials. Although the airborne route is not the most effective mode of transmission for the majority of known human pathogens, many viruses may be transmitted through this route (1). For example, measles, varicella zoster (2), and variola (3) viruses are naturally transmitted by aerosols. Other viruses, such as Newcastle disease virus, are particularly resistant to aerosolization and may potentially cause infections by the aerosol route (4, 5). On the other hand, the importance of aerosol transmission in the spread of some viruses, such as the influenza virus, is still a subject of debate (6).Aerosolized particles may be involved in viral transmission at short range through contamination of fomites by the rapid deposition of large droplets. However, true aerosol dissemination implies that sufficiently small infectious particles remain airborne for a prolonged period (2). Particles smaller than 5 m in aerodynamic diameter have the potential to travel long distances, as they sediment more slowly. However, these smaller particles harbor fewer viruses than larger particles but also less material that might protect the viruses in the airborne state. Indeed, viral resistance to aerosolization is partly dependent upon the composition of the droplet or droplet nuclei (5,7,8). Furthermore, the resistance of viruses to...

Advanced Analysis to Distinguish between Physical Decrease and Inactivation of Viable Phages in Aerosol by Quantitating Phage-Specific Particles

“…We confirmed the sensitivity, linearity, and specificity of the selected primer-probe set even in the presence of other environmental microbes. Using this quantitative PCR system and culture assay, we performed a behavior analysis of a phage aerosol at different levels of humidity, which is known to affect the viable number of airborne phi-X174 phages Nakanishi et al, 2012;Verreault et al, 2015 .…”

“…We selected a primer-probe set, set A, for PCR to robustly quantify phi-X174-specific airborne particles without being adversely affected by UV. Duchaine s research group had used another primer-probe set, set B Turgeon et al, 2014;Verreault et al, 2015;Turgeon et al, 2016. Ho et al 2016 had reported that the log reduction by UV of phi-X174 gene copies increased as the specific amplicon length for PCR increased.…”

Assessing microbial decontamination of indoor air with particular focus on human pathogenic viruses

“…27 The resistance of various phages to environmental stresses (RH, ultraviolet [UV], temperature, and aerosol duration) was studied, and it was shown that the response to stresses varied between the various models. 28 Phage MS2 has been the most broadly used surrogate in aerosol studies and is used mostly in biodefense to predict the fate and transport of biothreat agents. 29 Table 1 presents the phage models used and validated.…”

“…Environmentally controlled aerosol-aging chambers are designed to simulate environmental stresses that are imposed on microbial aerosols in order to understand the role of environmental parameters, such as temperature, UV, and RH, on the fate of airborne infectious agents. 28 Aerosols can remain airborne for prolonged periods in rotating chambers 31 because these particles remain suspended in a rotating mass of air. The gravitational forces exerted on the particles are countered by centrifugal forces created by the rotation of the drum.…”

“…The gravitational forces exerted on the particles are countered by centrifugal forces created by the rotation of the drum. 32 The effects on various viral and bacterial aerosols held at different levels of air temperature, RH, hydrogen peroxide vapor, UV radiation, ozone, and other physical and chemical agents can be studied using the rotating drum 28 (Caroline Duchaine, 2016). Figure 2 shows a picture of a rotating drum with the desiccants and the control panel.…”