Global Stability of a MERS-CoV Infection Model with CTL Immune Response and Intracellular Delay

In this paper, we propose and study a Middle East respiratory syndrome coronavirus (MERS-CoV) infection model with cytotoxic T lymphocyte (CTL) immune response and intracellular delay. This model includes five compartments: uninfected cells, infected cells, viruses, dipeptidyl peptidase 4 (DPP4), and CTL immune cells. We obtained an immunity-inactivated reproduction number R0 and an immunity-activated reproduction number R1. By analyzing the distributions of roots of the corresponding characteristic equations, the local stability results of the infection-free equilibrium, the immunity-inactivated equilibrium, and the immunity-activated equilibrium were obtained. Moreover, by constructing suitable Lyapunov functionals and combining LaSalle’s invariance principle and Barbalat’s lemma, some sufficient conditions for the global stability of the three types of equilibria were obtained. It was found that the infection-free equilibrium is globally asymptotically stable if R0≤1 and unstable if R0>1; the immunity-inactivated equilibrium is locally asymptotically stable if R0>1>R1 and globally asymptotically stable if R0>1>R1 and condition (H1) holds, but unstable if R1>1; and the immunity-activated equilibrium is locally asymptotically stable if R1>1 and is globally asymptotically stable if R1>1 and condition (H1) holds