Fig. 5.1.

The basic reproduction number ${\mathcal{R}}_0$ in terms of k. (a) ${\mathcal{R}}_0=1.0006$ as k = 0.1, the optimal strategy for reducing ${\mathcal{R}}_0$ to be less than 1 is to restrict the travel of infectious humans. (b) ${\mathcal{R}}_0=1.0002$ as k = 0.1, the optimal strategy for reducing ${\mathcal{R}}_0$ to be less than 1 is to restrict the travel of recovered humans.