Here, an SIRS model of disease spread with nonlinear incidence rate is studied, assuming that the total population is constant (). The rescaled system
is analyzed by means of qualitative analysis. The authors provide conditions under which the disease can persist (with one or two positive equilibria apart from the origin) or vanishes. Moreover, they give conditions for stability of the equilibria and existence and stability of periodic orbits. They show that for some parameters at least two periodic orbits appear, and examine cases under which the system undergoes Bogdanov-Takens bifurcation, supercritical and subcritical Hopf bifurcations, and homoclinic bifurcation.