Dynamics of SI epidemic with a demographic Allee effect

In this paper, we present an extended SI model of Hilker et al. (2009). In the presented model the birth rate and the death rate are both modeled as quadratic polynomials. This approach provides ample opportunity for taking into account the major contributors to an Allee effect and effectively captures species' differential susceptibility to the Allee effects. It is shown that, the behaviors (persistence or extinction) of the model solutions are characterized by the two essential threshold parameters lambda(0) and lambda(1) of the transmissibility lambda and a threshold quantity mu* of the disease pathogenicity mu. If lambda < lambda(0), the model is bistable and a disease cannot invade from arbitrarily small introductions into the host population at the carrying capacity, while it persists when lambda > lambda(0) and mu < mu*. When lambda > lambda(1) and mu > mu*, the disease derives the host population to extinction with origin as the only global attractor. For the special cases of the model, verifiable conditions for host population persistence (with or without infected individuals) and host extinction are derived. Interestingly, we show that if the values of the parameters alpha and beta of the extended model are restricted, then the two models are similar. Numerical simulations show how the parameter beta affects the dynamics of the model with respect to the host population persistence and extinction. (C) 2015 Elsevier Inc. All rights reserved.