Characterization of a Nose-Only Inhalation Exposure System for Ectromelia Virus Infection of Mice

Abstract

A nose-only inhalation exposure system (NOIES) was evaluated for its performance in this study using test polystyrene latex spheres (PLS) and ectromelia virus (ECTV), which is a surrogate for variola virus, the causative agent of smallpox. The test aerosol sampled at the various ports of the NOIES was found to be consistent in particle size and number concentration. ECTV bio-aerosol was delivered to A/J mice strain and the lethal dose (LD₅₀) value at which mortality was 50% was found to be 41 PFU/mL. The airborne ECTV particles were sampled and collected on TEM grids for particle size imaging using a scanning electron microscope (SEM) and structural integrity imaging using a transmission electron microscope (TEM). SEM images of ECTV after aerosolization showed the virions to be coated with the smaller size solute particles generated from the buffer solution during the aerosolization process. TEM images showed the ECTV to be structurally intact after undergoing the process of aerosolization. From the viable ECTV particle size distribution, the geometric mean diameter (GMD) of the airborne ECTV particles was calculated to be 278 nm with a geometric standard deviation (GSD) of 1.73.

Keywords:

• ectromelia virus bio-aerosol
• electron microscope imaging
• nose-only inhalation exposure system
• viable virus particle size distribution

Acknowledgments

This work was supported by NIAID NOI-AI-15436 (RMB) and National Institutes of Health grant U54 AI057160 to the Midwest Regional Center of Excellence for Biodefense and Emerging Infectious Disease Research (MRCE) (R.M.B., D.S., P.B.). We thank Monica Allen for administrative assistance, Ed Hembrador for assaying virus infectivity, and Erin Touchette, Jill Schriewer, Elsa Taricone, and Christina Zander for technical assistance.