Stability Analysis on an SIS Epidemiologic Model with Delay and a Variable Population Size

The delay existing in SIS epidemiologic model corresponds to an infectious period and disease-related deaths,and hence the population size becomes variable.In the model,the population dynamics structure includes the recruitment for natural deaths and the incidence term belongs to the simple mass action incidence.The thresholds and equilibrium were determined,and the stabilities were examined.The local stability of all kinds of equilibria and the global stability of the disease -free equilibrium.