R0 AND THE GLOBAL BEHAVIOR OF AN AGE-STRUCTURED SIS EPIDEMIC MODEL WITH PERIODICITY AND VERTICAL TRANSMISSION

In this paper, we study an age-structured SIS epidemic model with periodicity and vertical transmission. We show that the spectral radius of the Frechet derivative of a nonlinear integral operator plays the role of a threshold value for the global behavior of the model, that is, if the value is less than unity, then the disssease-free steady state of the model is globally asymptotically stable, while if the value is greater than unity, then the model has a unique globally asymptotically stable endemic (nontrivial) periodic solution. We also show that the value can coincide with the well-know epidemiological threshold value, the basic reproduction number R-0.