Abstract
Survival of respiratory viral pathogens in expelled saliva microdroplets is central to their transmission, yet the factors that determine survival in such microdroplets are not well understood. Here we combine microscopy imaging with virus viability assays to study survival of three bacteriophages suggested as good models for respiratory pathogens: the enveloped Phi6 (a surrogate for SARS-CoV-2), and the non-enveloped PhiX174 and MS2. We measured virus viability in human saliva microdroplets, SM buffer, and water following deposition on glass surfaces at various relative humidities (RH). Saliva and water microdroplets dried out rapidly, within minutes, at all tested RH levels (23%, 43%, 57%, and 78%), while SM microdroplets remained hydrated at RH ≥ 57%. Generally, the survival of all three viruses in dry saliva microdroplets was significantly greater than those in SM buffer and water under all RH (except PhiX174 in water under 57% RH survived the best among 3 media). Thus, atmosphere RH and microdroplet hydration state are not sufficient to explain virus survival, indicating that the virus-suspended medium, and association with saliva components in particular, likely play a role in virus survival. Uncovering the exact properties and components that make saliva a favorable environment for the survival of viruses, in particular enveloped ones like Phi6, is thus of great importance for reducing transmission of viral respiratory pathogens including SARS-CoV-2.
Highlights
Survival of respiratory viral pathogens in expelled saliva microdroplets is central to their transmission, yet the factors that determine survival in such microdroplets are not well understood
To study virus survival in microdroplets deposited on a smooth, inanimate surface, we sprayed Phi[6], MS2, and PhiX174 viruses suspended in three aqueous media—human saliva, water, and SM buffer—on glass-bottom 12-well plates (Fig. 1, “Methods”)
The sprayed well plates were placed under constant temperature and relative humidities (RH) conditions (23%, 43%, 57%, 78%) for 14 h, and subsequently microscopy images were taken and virus survival was estimated by the plaque assay using the corresponding bacterial host as a reporter for virus viability (Fig. 1, “Methods”)
Summary
Survival of respiratory viral pathogens in expelled saliva microdroplets is central to their transmission, yet the factors that determine survival in such microdroplets are not well understood. Uncovering the exact properties and components that make saliva a favorable environment for the survival of viruses, in particular enveloped ones like Phi[6], is of great importance for reducing transmission of viral respiratory pathogens including SARS-CoV-2. Microdroplets expelled from the human respiratory tract into the air through coughing, talking, and breathing are considered a key source of transmission of respiratory viruses including SARS-CoV-21,2. Survival is believed to depend upon the physicochemical characteristics and hydration conditions of the immediate microscopic environment of the virion These in turn are determined by several factors, including the composition of the fluid comprising the droplets, the surface properties, the ambient temperature, and the relative humidity (RH). We focus on two variables that directly affect MSW—solution composition and RH levels—and seek to determine whether and how it is reflected by virus survival trends
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