title: Backward bifurcations, turning points and rich dynamics in simple disease models.
abstract: In this paper, dynamical systems theory and bifurcation theory are applied to investigate the rich dynamical behaviours observed in three simple disease models. The 2- and 3-dimensional models we investigate have arisen in previous investigations of epidemiology, in-host disease, and autoimmunity. These closely related models display interesting dynamical behaviors including bistability, recurrence, and regular oscillations, each of which has possible clinical or public health implications. In this contribution we elucidate the key role of backward bifurcations in the parameter regimes leading to the behaviors of interest. We demonstrate that backward bifurcations with varied positions of turning points facilitate the appearance of Hopf bifurcations, and the varied dynamical behaviors are then determined by the properties of the Hopf bifurcation(s), including their location and direction. A Maple program developed earlier is implemented to determine the stability of limit cycles bifurcating from the Hopf bifurcation. Numerical simulations are presented to illustrate phenomena of interest such as bistability, recurrence and oscillation. We also discuss the physical motivations for the models and the clinical implications of the resulting dynamics.
authors.affiliation: Applied Mathematics, Western University, London, ON, N6A 5B7, Canada. zhang.wenjing14@gmail.com.
authors.forename: Wenjing
authors.identifier: 0000-0003-3451-7035
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Applied Mathematics, Western University, London, ON, N6A 5B7, Canada.
authors.forename: Lindi M
authors.initials: LM
authors.lastname: Wahl
authors.affiliation: Applied Mathematics, Western University, London, ON, N6A 5B7, Canada.
authors.forename: Pei
authors.initials: P
authors.lastname: Yu
mesh_terms: D003141:Communicable Diseases / Q000453:epidemiology; D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D011634:Public Health / Q000706:statistics & numerical data
keywords: Backward bifurcation; Bistability; Concave incidence rate; Convex incidence rate; Disease model; Forward bifurcation; Hopf bifurcation; Negative backward bifurcation; Positive backward bifurcation; Recurrence; Turning point