Stability of differential susceptibility and infectivity epidemic models

We introduce classes of differential susceptibility and infectivity epidemic models. These models address the problem of flows between the different susceptible, infectious and infected compartments and differential death rates as well. We prove the global stability of the disease free equilibrium when the basic reproduction ratio R-0 <= 1and the existence and uniqueness of an endemic equilibrium when R-0 > 1. We also prove the global asymptotic stabilit of the endemic equilibrium for a differential susceptibility and staged progression infectivity model, when R-0 > 1. Our results encompass and generalize those of Hyman and Li (J Math Biol 50:626-644, 2005; Math Biosci Eng 3:89-100, 2006).