Infectivity of Non-Enveloped Viruses Depends on Initial Droplet Size

RACHAEL SNODGRASS, Aaron Prussin II, Linsey Marr, Virginia Tech

     Abstract Number: 199
     Working Group: Bioaerosols

Abstract
When viruses carried in respiratory droplets are released into the air, the droplets may settle onto surfaces. The virions may then remain infectious on timescales sufficient to allow transmission to occur through contact with the droplets. Many environmental factors can impact the loss of infectivity of a virion in a droplet, including relative humidity (RH), temperature, viral structure, and the size of the droplet. It is well known that RH impacts the rate of virus inactivation, but there is a large gap in data pertaining to physiologically relevant droplet sizes. The objective of this experiment was to determine the effect of initial droplet size on the inactivation of the bacteriophage MS2, a model organism for non-enveloped viruses, at varying relative humidities. We quantified the loss of infectivity, or decay, of MS2 in two droplet sizes (1 µL and 1.8x10-4 µL) at three relative humidities (30, 50, 70 %) and four time points (0, 0.33, 1, 2 hours). A droplet-on-demand dispenser (DoD) was utilized to achieve a more physiologically relevant droplet size (1.8x10-4 µL) compared to a more traditional method of pipetting (1 µL). Droplets containing an initial titer of 4.18×1011 PFU/mL were dispensed on a superhydrophobic polystyrene petri dish and resuspended after the specified time for quantification of infectivity by plaque assay. We observed more rapid decay of virus in the small droplets generated by the DoD compared to the pipetted droplets. Overall, this experiment suggests that the stability of non-enveloped viruses is highly dependent on droplet size as well as other environmental factors. The study of physiologically relevant droplet sizes is essential to inform strategies for effective control of virus transmission.