Figure 2.

Numbers of infectious animals during the course of an hypothetical epidemic, for three modes of transmission of infection, (i) SI model in which infected animals remain infectious, (ii) SIR model in which infected animals recover so that they are no longer infectious and remain immune to the infection, (iii) SIRS model in which recovered animals lose their immunity and become immunologically susceptible again. Non-zero parameter values are identical for each model. Population size is 1000 animals.