Global stability of multigroup epidemic model with group mixing and nonlinear incidence rates

https://doi.org/10.1016/j.amc.2011.05.056Get rights and content

Abstract

In this paper, we introduce a basic reproduction number for a multigroup SEIR model with nonlinear incidence of infection and nonlinear removal functions between compartments. Then, we establish that global dynamics are completely determined by the basic reproduction number R0. It shows that, the basic reproduction number R0 is a global threshold parameter in the sense that if it is less than or equal to one, the disease free equilibrium is globally stable and the disease dies out; whereas if it is larger than one, there is a unique endemic equilibrium which is globally stable and thus the disease persists in the population. Finally, two numerical examples are also included to illustrate the effectiveness of the proposed result.

Introduction

Multigroup models have been proposed in the literature to describe the transmission dynamics of infectious diseases in heterogeneous host populations, such as measles, mumps, gonorrhea, HIV/AIDS, West-Nile virus and vector borne diseases such as Malaria. Heterogeneity in host population can be the result of many factors. Groups can be geographical such as communities, cities, and countries, or epidemiological, to incorporate differential infectivity or co-infection of multiple strains of the disease agent. Much research has been done on multigroup models, for example, see [1], [2], [3], [4], [5], [6] and references therein. It is well known that global dynamics of multigroup models with higher dimensions, especially the global stability of the endemic equilibrium, is a very challenging problem. The question of uniqueness and global stability of the endemic equilibrium, when the basic reproduction number R0 is greater than 1, has largely been open. Recently, the paper [7] proposed a graphtheoretic approach to the method of global Lyapunov functions and used it to establish the global stability of a unique endemic equilibrium of a multi-group SIR model with varying subpopulation sizes. Their result completely solved the open problem of the uniqueness and global stability of endemic equilibrium for this class of multi-group models. By using the results or ideas of [7], the papers [8], [9], [10], [11], [12], [13] investigated uniqueness and global stability of the endemic equilibrium for several class of multigroup models, with the basic reproduction number R0 is greater than 1, and some open problems were resolved.

In this paper, we consider a multigroup SEIR model with nonlinear incidence of infection and nonlinear removal functions between compartments. It covers many models in the literature, for example, the ones in [3], [4], [8], [10], [12], [14], [15]. The population is divided into n distinct groups (n  1). For 1  k  n, the kth group is further partitioned into four compartments: the susceptible, exposed, infectious, and recovered, whose numbers of individuals at time t are denoted by Sk(t), Ek(t), Ik(t) and Rk(t), respectively. The new multigroup epidemic model with group mixing and nonlinear incidence rates as follows:Sk=φk(Sk)-j=1nβkjfkj(Sk,Ij),Ek=j=1nβkjfkj(Sk,Ij)-μkgk(Ek),Ik=γkgk(Ek)-αkψk(Ik),Rk=pkψk(Ik)-qk(Rk),where φk(Sk) denotes the net growth of the susceptible class in the kth group, the nonlinear term βkjf(Sk, Ij) represents the cross infection from group j to group k; The matrix B = (βij)n×n is the irreducible contact matrix, where βij  0; γkgk(Ek) accounts for the progression of individuals in group k from the exposed class into the infectious class; μkgk(Ek), αkψk(Ik) and qk(Rk) denote the removal of the exposed, infectious and recovered classes in the kth group, respectively, which include the mortality of individuals in the above-mentioned classes; pkψk(Ik) denotes the production of the recovered individuals from infectious ones in the kth group. All constants μk, γk, αk and pk are assumed to be positive.

In Section 2, we first obtain that the basic reproduction number R0 is a global threshold parameter in the sense that if it is less than or equal to one, then the disease free equilibrium is globally asymptotically stable and the disease dies out; whereas if it is larger than one, there is a unique endemic equilibrium which is globally asymptotically stable and thus the disease persists in the population. And in Section 3, some numerical simulations are showed to illustrate the effectiveness of the proposed result.

Section snippets

Main results

Since the variables Rk do not appear in the first three equations of (1), we can work on the reduced system as follows:Sk=φk(Sk)-j=1nβkjfkj(Sk,Ij),Ek=j=1nβkjfkj(Sk,Ij)-μkgk(Ek),Ik=γkgk(Ek)-αkψk(Ik).For the functions gk, ψk and φk in (2), we assume that

  • (G1)

    gk, ψk are local Lipschitz on [0, ∞) with gk(0) = ψk(0) = 0, gk, ψk are continuous, positive, on (0, ∞), the function uψk(u) is non-increasing on (0,∞), and limu0+uψk(u)=δk for positive constant δk > 0;

  • (G2)

    φk are local Lipschitz on [0, ∞) with φk(0) > 0,

Numerical example

Consider the system (2) when k = 2, one has a two-group model as follows:S1=φ1(S1)-β11S1I11+I12+β12S1I21+I22,E1=β11S1I11+I12+β12S1I21+I22-μ1g1(E1),I1=γ1g1(E1)-α1ψ1(I1),S2=φ2(S2)-β21S2I11+I12+β22S2I21+I22,E2=β21S2I11+I12+β22S2I21+I22-μ2g2(E2),I2=γ2g2(E2)-α2ψ2(I2),wherefkj(Sk,Ij)=SkIj1+Ij2,k,j=1,2,φ1(u)=2-u,φ2(u)=3-u,g1(u)=g2(u)=ψ1(u)=ψ2(u)=uandγ1=12,α1=2,μ1=14,γ2=1,α2=13,μ2=3.If βij are chosen asβ11=524,β12=124,β21=136,β22=536,then we have R0 = 0.5 < 1, hence P0 = (2, 0, 0, 3, 0, 0) is the unique

Acknowledgement

This project is partially supported by a William and Mary Charles Center Biomathematics Summer Scholarship, NSF Grants DMS-1022648, DMS-0703532, EF-0436318 and William and Mary HHMI travel award.

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