Fig. 4.

Median incubation period versus dose. The kink in the middle of the curves for models A2 and D arises because the Sverdlovsk victims are assumed to have been exposed to an anthrax strain with an ID₅₀ of ≈8,600 spores, whereas the nonhuman primates in the studies cited here were exposed to the Ames strain with an ID₅₀ of ≈55,000 spores. Hence, the portion of the curve to the left of 1,000 spores assumes the lower ID₅₀ value and the portion to the right assumes the higher ID₅₀ value, thus causing a slight translation of the curve at 1,000 spores. Nonhuman primate data from Ivins et al. (33) and Gleiser et al. (27) (i.e., the open data points in Fig. 4) are shown for rough comparison only because either the number of nonhuman primates was too small or the time to death was not provided in these studies.