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. 2026 May 25;26:1377. doi: 10.1186/s12879-026-13589-9

Modeling the transmission dynamics of endemic meningitis: stability analysis and long-term persistence

Samaila Jackson Yaga 1,✉, Funmilayo Westnand Oshogboye Saporu 2
PMCID: PMC13386708  PMID: 42185774

Abstract

This study develops and analyzes a deterministic compartmental model to understand the transmission dynamics of Neisseria meningitidis under endemic conditions. Compartment profile plots illustrate the progression of the disease to an endemic level over time. Explicit expressions for the endemic equilibrium points and the basic reproductive number are derived. The basic reproductive number is decomposed into three interpretable components: contributions from (i) carriers, (ii) carriers progressing to symptomatic cases, and (iii) direct symptomatic cases (i.e., infectives bypassing carriership), highlighting the role of both carriers and infectives in long-term disease persistence. Sensitivity analysis identifies the transmission rate, the odds in favor of carrier infectivity, and the rate of loss of carriership as critical parameters influencing the basic reproductive number. Phase-plane plots (S–C and S–I) illustrate how variation in the basic reproductive number shapes the trajectory of convergence to the endemic equilibrium. Stability analysis shows that the endemic equilibrium is unstable when the product of the basic reproductive number and the susceptible population at equilibrium exceeds unity. Using Lyapunov functions and LaSalle’s invariance principle, we further show that the long-term dynamics are fully determined by this threshold: the disease-free equilibrium is globally asymptotically stable when the basic reproductive number is less than one, whereas a unique endemic equilibrium emerges and is globally stable when it is greater than one, demonstrating the persistence or elimination of meningitis depending on the threshold.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-026-13589-9.

Keywords: Endemic meningitis, Stability analysis, Endemic equilibrium, Sensitivity analysis, Phase plots, Basic reproductive number, Next generation matrix

Introduction

Meningitis, an acute inflammation of the meninges, remains a serious global public health concern due to its high mortality rates and severe neurological sequelae among survivors  [1]. The disease can be caused by a range of pathogens, including bacteria, viruses, and fungi, with bacterial meningitis posing the greatest threat due to its rapid progression and epidemic potential  [2, 3]. Among bacterial agents, Neisseria meningitidis is a leading cause of meningitis epidemics, especially in the African meningitis belt, a region stretching from Senegal to Ethiopia that experiences recurrent seasonal outbreaks  [4, 5].

The dynamics of meningitis transmission are influenced by a complex interplay of climatic, demographic, and behavioral factors. Seasonal variations in temperature, humidity, and dust levels have been strongly associated with increased disease incidence, particularly during the dry season  [6, 7]. Furthermore, the disease’s epidemiology is modulated by age-specific susceptibility, with the highest burden observed among children under five years, adolescents, and young adults  [8]. In endemic settings, asymptomatic carriage plays a critical role in maintaining transmission, with carriers serving as reservoirs for the spread of pathogenic strains  [9–11].

Given the significant public health burden of meningitis, mathematical models have emerged as vital tools for understanding the disease’s dynamics and informing control strategies. Mathematical models allow for the exploration of key epidemiological factors, the prediction of disease outcomes under various intervention scenarios and the identification of critical thresholds for disease control  [12, 13].

Endemic models are particularly important for characterizing the conditions under which meningitis persists within a population and for evaluating the effectiveness of long-term intervention strategies. Deterministic models have been widely employed to study meningitis dynamics in endemic settings  [14–19]. Most of these studies focus on assessing the impact of vaccination strategies, often incorporating age structure into the modeling framework. More recently, Mustapha et al. [20] integrated the effects of carrier diagnosis and prophylactic treatment on meningitis transmission dynamics.

In contrast, stochastic and deterministic models developed under epidemic settings in  [11, 21] excluded demographic turnover and long-term endemic behavior. These works extended the epidemic framework of Irving et al. [17] by incorporating two disease stages (infection with and without complications), allowing a fraction of susceptible individuals to transition directly to the infectious class without passing through the carrier state, and accounting for differential transmission rates between carriers and infectives.

In this study, we develop a deterministic model for meningitis endemicity, building on the framework of [11]. The primary objective is to elucidate the key mechanisms governing the transmission dynamics, stability, and long-term persistence of meningitis under endemic conditions. Specifically, we aim to:

  • (i)

    establish conditions for the local and global stability of the endemic equilibrium,

  • (ii)

    characterize the long-term persistence of meningitis in the population, and

  • (iii)

    compare two model formulations to assess the impact of alternative infection pathways on equilibrium behavior and the convergence of solution trajectories.

The model

Mathematical models are essential for elucidating disease transmission mechanisms, enabling the description, prediction, and analysis of epidemic behavior and long-term dynamics. This study employs a compartmental framework to model the dynamics of meningococcal infection, balancing mathematical simplicity and analytical tractability. As depicted in Fig. 1, the population is divided into six epidemiological compartments: susceptible (Inline graphic), asymptomatic carrier (Inline graphic), symptomatic infective (Inline graphic), infective with complications (Inline graphic), recovered/immune (Inline graphic), and meningitis-related deaths (Inline graphic). Disease transmission is driven by the interactions between the Inline graphic and Inline graphic compartments, as individuals in Inline graphic are incapacitated due to disease severity. Susceptible individuals (Inline graphic) acquire infection through infective contact with carriers (Inline graphic) or infectious individuals (Inline graphic) at a transmission rate Inline graphic. The force of infection, Inline graphic, is given by:

graphic file with name d33e327.gif 1

Fig. 1.

Fig. 1

Compartmental diagram for endemic meningitis transmission process

In this model, Inline graphic represents the odds ratio favoring the infectious potential of carriers compared to symptomatic individuals, while Inline graphic denotes the total population size. Demographic parameters of birth (Inline graphic) and natural death (Inline graphic) rates are introduced to reflect the endemic nature of the disease. The compartmental diagram and the equations governing the dynamics are provided below. Birth and death rates are set equal (Inline graphic) to ensure a constant population size Inline graphic throughout time,t, under consideration.

graphic file with name d33e367.gif 2

where

graphic file with name d33e374.gif

Dividing the equations by Inline graphic converts them into proportions and the system of equations are given below.

graphic file with name d33e383.gif 3

where

graphic file with name d33e389.gif

Table 1 presents the definitions, values, and sources of all model parameters.

Table 1.

Description of parameter values used in the model and their possible range of values

S/No. Parameter Description Values / Range (Inline graphic) Source
1 Inline graphic Transmission rate 25–200  Irving et al. [17]
2 Inline graphic Odds in favor of carrier infecting a susceptible over an infective 0.5–10 [11]
3 Inline graphic Proportion of Inline graphic moving to Inline graphic 0–1 [17]
4 Inline graphic Rate of loss of carriership 1–52 [17]
5 Inline graphic Rate at which a carrier becomes stage one infective Inline graphic [17]
6 Inline graphic Rate at which stage one infective develops complication Inline graphic [1],
7 Inline graphic Recovery rate of stage one infective 20–52 [17]
8 Inline graphic Recovery rate of individuals with complication 20–52 Assumed
9 Inline graphic Rate at which recovered individuals lose immunity 0.04–2 [17]
10 Inline graphic Disease-induced death rate Inline graphic [17]

Two special cases of model Eq. (2) are of interest here: Model I (Inline graphic) and Model II (Inline graphic). Model profile plot for proportions in each of the compartment for various values of demographic and epidemiological parameters for models I and II are given in Fig. 2.

Fig. 2.

Fig. 2

Proportions of individuals in each compartment under varying demographic parameter rates (Inline graphic and Inline graphic). The rows correspond to Inline graphic (top), Inline graphic (second), Inline graphic (third), and Inline graphic (bottom). Initial conditions: Inline graphic

Figure 2 indicates that the introduction of the demographic parameters has allowed the progression of the transmission of the disease to endemic level over time, irrespective of the variation in the birth (=death) rates and the two models considered. The drift to equilibrium level is particular obvious for Susceptible, Carrier, Infective and Infective stage one profiles. These prompt a suspicion of convergence to an equilibrium point. It must be noted however that the convergence to equilibrium point is not sufficient for asymptotic stability  [22].

There are obvious differences in the trajectory of the profiles exhibited for models I and II. These are listed below.

  • i.

    Time to equilibrium is very much shorter for Model II than Model I

  • ii.

    Model I approaches equilibrium with noticeable damped oscillation not present in model II.

  • iii.

    Values at equilibrium point are remarkably higher for model II in the recovered and death compartments and slightly so for carrier, infective and infective stage one compartments.

  • iv.

    For the susceptible compartment, it is the values for model I that are remarkably higher.

These are the underlying differences in the profiles of Model I and Model II that should be noted particularly when Model II is intended to be used as an approximating system to model I for inferential purpose.

The basic reproductive number

The basic reproductive number, Inline graphic, is a fundamental threshold parameter in epidemiology, determining the conditions for endemic stability and the potential for epidemic outbreaks. It is defined as the expected number of secondary cases generated by a single infected individual in a fully susceptible population. The derivation of Inline graphic follows the next-generation matrix framework proposed by Diekmann et al. [23], which offers a robust mathematical approach for compartmental models. This method involves decomposing the system into a transmission matrix (Inline graphic), representing the rates of new infections, and a transition matrix (Inline graphic), describing the progression through infection compartments. Here these matrices are expressed as follows:

graphic file with name d33e729.gif 4

and

graphic file with name d33e735.gif 5

The next generation matrix, Inline graphic, is obtained by calculating Inline graphic, where Inline graphic is the inverse of the transition matrix. The matrix Inline graphic contains the rate at which new infections are produced and their transitions through different states. To calculate Inline graphic, we take the spectral radius (the largest eigenvalue) of the matrix Inline graphic.The inverse of the transition matrix Inline graphic is given by

graphic file with name d33e770.gif

and

graphic file with name d33e775.gif 6

The spectral radius of Inline graphic, which corresponds to the basic reproductive number Inline graphic, is given by

graphic file with name d33e789.gif 7

This formulation highlights Inline graphic as the sum of three components, each representing a distinct pathway contributing to the transmission of infection within the population. The expression can be rewritten to emphasize specific transmission pathways, as

graphic file with name d33e799.gif 8

where:

graphic file with name d33e805.gif

Notice the similarity between the expression for Inline graphic here and that for the epidemic case given (equation 2b) in Yaga et al. [11] as

graphic file with name d33e817.gif 9

Interpretation of the components of Inline graphic

  • i)

    Inline graphic: This is the number of secondary infections produced by a carrier during the average duration time of carriership.

  • ii)

    Inline graphic: This is the number of secondary symptomatic infections that passed through carriership that are produced by a symptomatic infective during an average duration of an infectious period.

  • iii)

    Inline graphic: This is the number of secondary symptomatic infectives that become infective directly, without passing through carriership produced by a symptomatic infective during an average duration of an infectious period.

When Inline graphic, the disease persists and establishes endemicity. The components of Inline graphic quantify contributions from different stages of infection to overall transmission dynamics in moving towards an established endemicity level. The rate of this progression is clearly determined by contributions from carriers and symptomatic infectives. This understanding can provide an informed decision in the design of any containment strategies aimed at reducing the spread of meningitis. This will inevitably entail making Inline graphic.

Sensitivity analysis

It must be mentioned here that the focus is on the influence of the parameters in the model on Inline graphic. While a discussion of Inline graphic would provide a clearer understanding of how its components are influenced, this is not the primary concern here. From Table 2, it is clear that Inline graphic or any of its components is not sensitive to Inline graphic (birth/death rate). This is a clear indication that the epidemic (Eq. (9), [11]) and the endemic (Eq. (8)) Inline graphic, provide similar conclusions about the understanding of the transmission of meningitis.

Table 2.

Sensitivity analysis for parameters of Inline graphic and its components Inline graphic, Inline graphic, and Inline graphic.This sensitivity indices are derived using the normalized forward sensitivity analysis method

Param Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
Response Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic — — Inline graphic
Inline graphic Inline graphic — Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
Inline graphic Inline graphic — — — Inline graphic Inline graphic Inline graphic Inline graphic
Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic

The parameters with the highest indices for endemic Inline graphic are Inline graphic and Inline graphic with Inline graphic and Inline graphic each having positive values, while the value for Inline graphic is negative. This implies that when Inline graphic and Inline graphic are respectively increased, endemic Inline graphic will increase, while it will decrease when Inline graphic is increased. The epidemic Inline graphic on the other hand has only Inline graphic and Inline graphic with positive indices. Notice that there is an additional sensitive parameter, Inline graphic, for the endemic Inline graphic over that for the epidemic. Consequently the distinction between the two Inline graphic have been clearly identified.

The values of endemic Inline graphic for various values of Inline graphic and Inline graphic are presented in Table 3. It is noticed that as the value of Inline graphic decreases the value of Inline graphic increases irrespective of Inline graphic considered. In particular, for Inline graphic for all values of Inline graphic considered. That is, in this cases the disease will persist and progress to endemicity.

Table 3.

Effect of Inline graphic and Inline graphic on Inline graphic, for Inline graphic, Inline graphic, Inline graphic, Inline graphic, Inline graphic, Inline graphic, Inline graphic

Inline graphic
Inline graphic 0.5 1 2 3 4
0.5 Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
0.5 Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
10 Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
15 Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
20 Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
25 Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
30 Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic

As Inline graphic denote the rate of carrier conversion to a susceptible state and Inline graphic denotes the odd in favor of a carrier transmitting infection, Table 3 clearly establishes the significant role carrier state plays in driving the disease transmission to endemicity as was also noted in the epidemic case  [11] This is not surprising as carriers serve as reservoirs for the spread of pathogenic strains. Consequently the carrier state must be approximately targeted for any control intervention to be successful.

Endemic equilibrium

Endemic models typically incorporate demographic processes, capturing disease persistence in a long-term within populations. To analyze system behavior at equilibrium, we set the equations in (2) to zero and solve for the state variables satisfying these conditions. These variables define the endemic equilibrium points. For the disease-free equilibrium, the system yields a trivial solution  [13]. The disease-free equilibrium point for the system in (2) is denoted by

graphic file with name d33e1601.gif 10

To establish the endemic-equilibrium point is not a trivial exercise. Setting the system of Eq. (2) to zero we have

graphic file with name d33e1610.gif 11

For simplicity, let Inline graphic, Inline graphic and Inline graphic. Due to the complexity of the system of equations we use Maple Version 18 to solve the system of equation in (11). This gives the endemic equilibrium point as

graphic file with name d33e1631.gif

The solution reveals the existence of an endemic equilibrium point. This point is characterised using S-C and S-I phase plots presented in Fig. 3. A comparison of these plots indicate no observable distinction between the two for a given Inline graphic. However, notable differences emerge in the pattern of the spirals as the basic reproduction number Inline graphic approaches one. Specifically, when Inline graphic, the phase plots display damped oscillations that gradually converge to the endemic equilibrium. In contrast, when Inline graphic , the convergence to the endemic equilibrium occurs with very little observable oscillatory behavior. These characteristics are depicted clearly in Fig. 3.

Fig. 3.

Fig. 3

Phase portraits in the proportion of susceptible and carrier (Inline graphic–Inline graphic) and susceptible and infective (Inline graphic–Inline graphic) planes for varying values of the basic reproduction number Inline graphic and Inline graphic. The trajectories illustrate convergence toward a unique endemic equilibrium. For Inline graphic, the system exhibits damped oscillatory behavior before settling at equilibrium, whereas for Inline graphic, convergence occurs with minimal oscillations, indicating a stronger attracting endemic state as transmission intensity increases

Figure 4 shows the plot of profiles for S, C, and I compartments for varying values of Inline graphic. In Table 4 we are able to extract estimates from Fig. 4 that provide a good epidemiological insight on the endemic equilibrium point. It is clear from the table that the endemic equilibrium point is reached faster as Inline graphic is greater than one. It is noticeable that for a high Inline graphic (=3.9575) equilibrium point is reached only after ten years with only 15% of the susceptible population remaining. This proportion of susceptible population left is not sufficient to start an epidemic. However, with the influx of new susceptible from birth it can trigger persistence of the disease at low endemic level.

Fig. 4.

Fig. 4

Time profiles of the proportion of susceptible (Inline graphic), carrier (Inline graphic), and infectious (i) compartments for different values of the basic reproduction number Inline graphic and Inline graphic. Increasing values of Inline graphic lead to faster convergence toward the endemic equilibrium and a lower equilibrium proportion of susceptibles, reflecting enhanced transmission and sustained endemic persistence

Table 4.

Epidemiological characteristics of the endemic equilibrium for different values of the basic reproduction number Inline graphic, including equilibrium time Inline graphic and compartmental proportions at equilibrium

Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic Inline graphic
0.7659 50 0.8984077 0.000274101 0.00016677 0.00019358 0.046189537 0.10019298
1.0000 40 0.70346581 0.001241955 0.00055723 0.00064660 0.152043380 0.23011395
1.2166 20 0.39537551 0.003878285 0.00143057 0.00165958 0.39077402 0.26891620
3.9575 10 0.14469764 0.016824061 0.00230515 0.002675064 0.63674375 0.23544029

Stability analysis

In theoretical epidemiology, stability analysis plays a crucial role in understanding the long-term behavior of disease dynamics. It focuses on whether solutions to dynamical system models converge to equilibrium points, indicating whether a disease will die out, persist, or reach a stable endemic state. Smooth convergence suggests a stable balance between disease transmission and control measures, while oscillatory behavior may signal periodic disease outbreaks influenced by complex population interactions or external factors. Analyzing these dynamics provide valuable insights into epidemic control strategies and the conditions required for disease eradication or sustained management.

The stability of equilibrium points are determined analytically  [13]) using the Jacobian of the system of differential equation in (3), given as:

graphic file with name d33e1902.gif 12

We first consider the stability of the endemic equilibrium point Inline graphic as that of the disease equilibrium point Inline graphic is a special case of this.The Jacobian mattrix evaluated at the endemic equilibrium point Inline graphic is given by

graphic file with name d33e1920.gif 13

The eigenvalues of the Jaciabn (Inline graphic) are

graphic file with name d33e1930.gif 14
graphic file with name d33e1934.gif 15
graphic file with name d33e1938.gif 16
graphic file with name d33e1942.gif 17
graphic file with name d33e1946.gif 18
graphic file with name d33e1950.gif 19

We simplify Inline graphic further.

graphic file with name d33e1960.gif

where

graphic file with name d33e1965.gif

where

graphic file with name d33e1970.gif

substituting into Inline graphic and Inline graphic we have

graphic file with name d33e1983.gif

and

graphic file with name d33e1988.gif

It is clear that the eigenvalue Inline graphic is positive only if Inline graphic. Consequently, the endemic equilibrium point Inline graphic is asymptotically unstable. By extension, the disease free equilibrium point, Inline graphic is also asymptotically unstable when Inline graphic. This implies that there is disease persistence in the long term due to renewed number of susceptibles through birth but that the endemic equilibtium point is asymptotically unstable to small perturbations when Inline graphic. This is another example that shows that convergence to an equilibrium point is not sufficient for asymptotic stability as pointed out in [22]. Of course if Inline graphic the disease free equilibrium is stable because the pathogen cannot invade if each infected host passes on the infection to fewer than one other host.

Global stability analysis

Global stability of the disease-free equilibrium

Global stability is commonly established through the construction of an appropriate Lyapunov function whose time derivative along solutions of the system is negative definite  [24–26]. The use of linear Lyapunov functions involving infected compartments to establish global stability of the disease-free equilibrium (DFE) is well established in epidemic modeling Hethcote [27].

Let Inline graphic be a Lyapunov function defined as a linear combination of the infected states, namely the carrier class Inline graphic and the infectious class Inline graphic, given by

graphic file with name d33e2054.gif 20

where Inline graphic and Inline graphic are constants to be determined. Taking the time derivative of Inline graphic along solutions of the system yields

graphic file with name d33e2072.gif 21

Substituting the corresponding expressions for Inline graphic and Inline graphic from the original system of Eq. (2), we obtain

graphic file with name d33e2089.gif 22

where Inline graphic denotes the force of infection. Rearranging terms, we separate the transmission and transition components as follows:

graphic file with name d33e2099.gif 23

To relate this expression to the basic reproduction number Inline graphic, we equate the coefficient of the transmission term with the numerator of Inline graphic, and the transition terms with its denominator. This leads to the system

graphic file with name d33e2113.gif 24a
graphic file with name d33e2117.gif 24b
graphic file with name d33e2121.gif 24c

Solving Eq. (24a)–(24c) yields

graphic file with name d33e2133.gif 25

which are clearly positive. Substituting these expressions together with the force of infection Inline graphic into Eq. (23), we obtain

graphic file with name d33e2146.gif 26

The expression can be factored in terms of Inline graphic only when Inline graphic, corresponding to the case where carriers and infectious individuals have equal transmission potential. This assumption is therefore crucial for establishing global stability.

Under this condition, factoring out Inline graphic yields

graphic file with name d33e2166.gif 27

From the positivity and boundedness result established in Theorem 1, the susceptible population satisfies Inline graphic. For a closed population where birth balances natural death (Inline graphic), we have Inline graphic. Consequently, the above expression reduces to

graphic file with name d33e2188.gif 28

It follows immediately that Inline graphic if and only if Inline graphic. By LaSalle’s Invariance Principle  [28], every solution of the system (2) with initial conditions in the positively invariant region Inline graphic (see supplementary sheet) approaches the disease-free equilibrium Inline graphic as Inline graphic.

Hence, the disease-free equilibrium Inline graphic is globally asymptotically stable in Inline graphic whenever Inline graphic.

The Lyapunov function establishing this result is given by

graphic file with name d33e2237.gif 29

Global asymptotic stability of the disease-free equilibrium is therefore guaranteed under the assumptions that carriers and infectious individuals have equal transmission potential (Inline graphic) and that the population is demographically closed (Inline graphic). Under these conditions, regardless of how far the initial conditions are from the disease-free equilibrium, the system converges to Inline graphic in the long run when Inline graphic; otherwise, the disease-free equilibrium is globally unstable.

Global stability of disease endemic equilibrium

The global stability of the endemic equilibrium point is determined by constructing a Lyapunov function, such that the derivative of this function is less than zero. The Lyapunov function defined as Inline graphic is the Goh-Voltera-type  [27, 29]. Here is given as

graphic file with name d33e2273.gif 30

Taking first derivative of the Lyapunov function Inline graphic, we have

graphic file with name d33e2283.gif 31

substituting the right hand side of the system of equations in (2) into each component in Eq. (31) we have:

graphic file with name d33e2295.gif 32

we substitute the value of Inline graphic with its corresponding value at the endemic equilibrium point, as Inline graphic and substitute into (31), we have

graphic file with name d33e2312.gif

where Inline graphic. At endemic equilibrium point, Inline graphic. Using the normal procedure, we obtain the following for the remaining components of (30)

graphic file with name d33e2328.gif

substituting the inequalities into Eq. (31) and simplify, we have

graphic file with name d33e2336.gif 33

where Inline graphic and Inline graphic is collapsed by first and second component of (31). By direct calculations,

graphic file with name d33e2353.gif

similarly, we have

graphic file with name d33e2358.gif

Here, by substituting all the corresponding expressions into the Lyapunov function, and for a suitable choice of Inline graphic and Inline graphic, the Goh-Volterra type Lyapunov function satisfies Inline graphic, with equality Inline graphic holding in the limiting case.

graphic file with name d33e2379.gif 34

We set Inline graphic and Inline graphic in the expression for Inline graphic, which then becomes

graphic file with name d33e2397.gif 35

To ensure that Inline graphic, the equality Inline graphic holds if and only if

graphic file with name d33e2412.gif

Therefore, the endemic equilibrium point Inline graphic is the only positively invariant set in Inline graphic satisfying

graphic file with name d33e2425.gif

It then follows from LaSalle’s invariance principle  [28] that every solution of the system in (2) with initial conditions in the invariant manifold Inline graphic (see Supplementary sheet) converges to the endemic equilibrium point Inline graphic as Inline graphic. Hence, the positive endemic equilibrium is globally asymptotically stable when Inline graphic, since the endemic equilibrium exists only for Inline graphic.

Conclusion

In this study, a six-compartment deterministic model proposed in Yaga and Saporu (2024) was extended to investigate the transmission dynamics of meningococcal meningitis in an endemic setting. Two model variants (Model I: Inline graphic and Model II: Inline graphic) were examined to compare disease dynamics under differing assumptions on infection pathways.

Compartmental profile plots under varying birth–death rates demonstrated the system’s tendency to converge toward an endemic equilibrium, with Model II exhibiting faster convergence and higher endemic levels in the recovered and death compartments compared to Model I. Notably, the presence or absence of damped oscillations in these trajectories further distinguished the two models, indicating differences in temporal disease dynamics.

An explicit expression for the basic reproductive number was derived and decomposed into three interpretable components: Inline graphic, representing the contribution from carriers; Inline graphic, accounting for carriers progressing to symptomatic infection; and Inline graphic, corresponding to direct symptomatic infections. Sensitivity analysis revealed that the basic reproductive number is most responsive to the transmission rate (Inline graphic), the odds in favour of carrier infectivity (Inline graphic), and the rate of loss from the carrier state (Inline graphic). Notably, unlike epidemic settings, the endemic reproductive number also exhibits sensitivity to the carrier transmission pathway, further emphasizing the critical role of carriers in sustaining long-term disease persistence.

A detailed equilibrium analysis established the existence of both disease-free and endemic equilibrium points. Numerical investigations showed that the time required to reach the endemic equilibrium decreases as the basic reproductive number increases. Importantly, even when only a small fraction of the population remains susceptible at equilibrium, the continuous influx of new susceptibles through births ensures the persistence of the disease at low endemic levels.

Local stability analysis  [13, 30], based on Jacobian matrices and eigenvalue decomposition, showed that the endemic and disease-free equilibria are asymptotically unstable when Inline graphic and Inline graphic, respectively, indicating that small perturbations can lead to divergent dynamics in these regimes. As expected, when Inline graphic, the disease dies out.

Using Lyapunov functions and LaSalle’s invariance principle, we further established that the global dynamics of the model are fully governed by the basic reproductive number: the disease-free equilibrium is globally asymptotically stable when the basic reproductive number is less than one, whereas a unique endemic equilibrium emerges and is globally asymptotically stable when the basic reproductive number exceeds one. This result rigorously confirms the threshold-driven persistence or elimination of meningococcal meningitis in the population.

Overall, this work provides a rigorous mathematical foundation for understanding endemic meningitis dynamics and offers valuable insights for targeted intervention strategies, particularly those aimed at asymptomatic carriers, to achieve long-term disease control and potential elimination.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Supplementary Material 1 (129.1KB, pdf)

Author contributions

S.J.Y. conceived and designed the study, developed the mathematical model, and performed the theoretical analysis. F.W.O.S. provided supervision, guidance on model formulation, and critical revisions to the manuscript. S.J.Y. wrote the first draft of the manuscript. Both authors contributed to interpretation of the results, reviewed the manuscript, and approved the final version for submission.

Funding

Not applicable.

Data availability

The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The author declares no competing interests.

Footnotes

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Material 1 (129.1KB, pdf)

Data Availability Statement

The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request.


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