FIG. 1.

Experimental data. (a to c) The numbers of uninfected (blue) and infected (red) respiratory epithelial cells were determined for each bronchiole in a left cranial lung sample from archived samples from an experimental infection of three immunologically naïve horses. The distribution of infection is shown for 2.5 (a), 4.5 (b), and 5.5 (c) days postinfection. The bronchioles were sorted in ascending order with respect to the number of epithelial cells they contained. (d) Total percentages of infection at 2.5, 4.5, and 5.5 days postinfection were determined to be 1.93%, 4.73%, and 1.87%, respectively (circles). A simple function (solid curve) was interpolated to these data points to estimate the cumulative percentage of cells infected over the course of infection (27%).