Proportional mouse model for aerosol infection by influenza

Abstract

Aims: The aim of this study was to demonstrate a prototype tool for measuring infectivity of an aerosolized human pathogen - influenza A/PR/8/34 (H1N1) virus - using a small-animal model in the Controlled Aerosol Test System (CATS).

Methods and results: Intranasal inoculation of nonadapted H1N1 virus into C57BL, BALB/c and CD-1 mice caused infection in all three species. Respiratory exposure of CD-1 mice to the aerosolized virus at graduated doses was accomplished in a modified rodent exposure apparatus. Weight change was recorded for 7 days postexposure, and viral populations in lung tissue homogenates were measured post mortem by DNA amplification (qRT-PCR), direct fluorescence and microscopic evaluation of cytopathic effect. Plots of weight change and of PCR cycle threshold vs delivered dose were linear to threshold doses of ~40 TCID(50) and ~12 TCID(50) , respectively.

Conclusions: MID(50) for inspired H1N1 aerosols in CD-1 mice is between 12 and 40 TCID(50) ; proportionality to dose of weight loss and viral populations makes the CD-1 mouse a useful model for measuring infectivity by inhalation.

Significance and impact of the study: In the CATS, this mouse-virus model provides the first quantitative method to evaluate the ability of respiratory protective technologies to attenuate the infectivity of an inspired pathogenic aerosol.

Figure 1

Schematic of the Controlled Aerosol Test System (CATS). Live virus aerosols were used to determine MID ₅₀ of Influenza A/PR/8/34 (H1N1) in a live animal model. Each mouse's nose (arrow) penetrates from a radially oriented constraint through the perimeter of the nose‐only inhalation exposure system (NOIES).

Figure 2

Photograph of Controlled Aerosol Test System (CATS), with key components labelled. Not pictured: control panel, constraints and impinger hook‐up.

Figure 3

(a, b) Mouse lung image after exposure to aerosolized virus; H&E staining technique. (c, d) Mouse lung image after exposure to sterile aerosols (no virus noted).

Figure 4

Size dependence in coefficient of variation of sodium chloride particle counts among ports of the CATS.

Figure 5

Average weight change for mouse exposure groups over three different received aerosol doses:  = 1 : 30 dilution series;  = 1 : 300 dilution series;  = 1 : 1000 dilution series. Plot shows overlap between doses received and change in weight, MID ₅₀ ≤ intercept of line with control value.