Global Dynamics Analysis of a Cholera Transmission Model with General Incidence and Multiple Modes of Infection ()
1. Introduction
Cholera, a grave waterborne ailment caused by Vibrio cholerae, exhibits a remarkable ability to persist in certain aquatic environments for durations spanning three months to two years. Its clinical manifestations are characterized by intense diarrhea and vomiting, with severe cases leading to potentially fatal dehydration due to significant loss of bodily fluids and electrolytes. Categorized as a class A infectious disease in China, cholera is distinguished by its sudden onset and rapid transmission dynamics. The primary mode of transmission involves the interaction between humans and their environment, particularly through the ingestion of food or water contaminated by the Vibrio cholerae bacteria [1] [2]. Additionally, a secondary transmission route occurs through direct human-to-human interactions, specifically close contact with infected individuals [3] [4]. Globally, cholera imposes a substantial burden, resulting in 3 - 5 million new infections annually and causing 28,800 - 130,000 deaths each year. Despite a typically low mortality rate of under five percent, this rate can skyrocket to fifty percent in regions where access to treatment is limited. Children, especially in Africa and Southeast Asia, bear the brunt of this disease’s impact. Cholera continues to pose a significant public health threat in developing nations, attracting sustained attention and research interest from scholars [5]-[10].
Significantly, Wang et al. [8] introduced a distinctive SIBR cholera transmission model, encompassing both direct human-to-human and indirect environment-to-human transmission pathways:
(1.1)
In this framework, the entire human population, denoted by the constant size N, is categorized into distinct compartments: the susceptible (S), the infectious (I) and the recovered (R) [11] [12] [13]. Additionally, there is an auxiliary compartment B to quantify the concentration of Vibrio in contaminated water. The transmission rates and bacterial shedding rates are contingent upon the number of infectious individuals. Within this context, the parameters are defined as follows:
represents the natural mortality rate,
signifies the net mortality rate of bacteria,
denotes the recovery rate,
represents the rate of host immune loss,
represents the infection rate of patients, influenced by the virus’s spread function
. Furthermore,
signifies the host shedding rate. It stands to be reasonable that all the parameters keep nonnegative.
Furthermore, this model accounts for the influence of human behavior arising from health education, improved hygiene, and sanitation practices [14] [15]. Importantly, given that immunity gradually wanes, individuals who have recovered from cholera remain susceptible to reinfection after a certain period. Studies findings indicate that diminished exposure due to altered human behavior can lead to a reduction in the scale of both epidemics and endemic diseases. Building upon the concepts used in [8], we delve into a more comprehensive model. Specifically, we explore the properties of a generalized SIBR cholera transmission model with a broadened incidence function. The proposed model is expressed as follows:
(1.2)
Assume that the total population is constant
. The model is based on the standard SIR (susceptibility-infection-recovery) compartment structure and has an additional compartment B indicating the concentration of Vibrio cholera in contaminated water. Based on the above assumptions, model (1.2) can be established [16] [17] [18].
The structure of this article unfolds as follows: Section 1 is the proof of the positivity and boundedness of solutions for the model (1.2). Section 2 is dedicated to establishing the existence and stability of equilibria, encompassing both the disease-free equilibrium and the positive equilibrium points. Some numerical simulations and sensitivity analyses are performed in Section 3 for the parameter
, corroborating the theoretical analysis mentioned earlier. Finally, the article concludes in Section 4 with a concise discussion summarizing our findings.
2. Positive and Boundedness of Solutions
2.1. Positivity of Solutions
Theorem 2.1. Under nonnegative initial conditions, for
, the solution
of model (1.2) is nonnegative.
Proof. Let
. Now, from the first equation of model (1.2), we obtain
.
From the above equation, we can reduce that
Further,
Therefore,
Similarly, we can obtain the bounds for the other components of the solution.
2.2. Boundedness of Solutions
Theorem 2.2. All solutions of model (1.2) are bounded.
Proof. The model (1.2) consists of two populations, namely human and pathogen. Therefore, we will break the model (1.2) into two parts, of which one involves the human population
and the other the pathogen population B. According to model (1.2) we obtain
Further, from the first equation of the model (1.2), we have
Hence, we conclude that
. Now, from the last equation of the model, we deduce that
. We can obtain
. According to the third equation of the model (1.2) and assumptions in reference [8], we can arrive at
Therefore,
. From the above discussion, it is clear from the above discussion that all solutions are bounded. Next, we obtain the feasible region for the human population as
And the feasible region for pathogen population is
Define
. Now,
is a positively invariant region for the model (1.2). Moreover, the model (1.2) is mathematically and epidemiologically well-posed with the method utilized in [19].
3. Main Content
3.1. The Existence of the Equilibria
The existence of equilibria is discussed below, we define
Theorem 3.1 When
, then model (1.2) has two equilibria
and
, when
, model (1.2) has a unique equilibrium
.
Proof. Due to
,
, and
Because of
, then
. Thus, considering
and
at the intersection where
Thus, we can obtain
This indicates that
, On the other hand
and
, then
Therefore, when
,
is the only one node, denoted as
. When
,
, there is no node. With the utilization of next generation matrix method mentioned in [20] [21], the matrix sum F and V can be written as
Therefore, the basic reproduction number
of the model can be obtained as follows
At the same time, if disease control targets at a particular host type, a useful threshold is called the reproduction number T. The reproduction number defines the expected number of secondary infections due to a typical primary case in a fully susceptible population [22] [23]. It is an extension of the basic reproduction number
. According to literature [23], it is concluded that
. In the following analysis, we will use both and realize that the two are equivalent in characterizing the disease threshold dynamics.
3.2. Stability of Disease-Free Equilibrium E0
Theorem 3.2.1. When
, the disease-free equilibrium point of model (1.2) is locally asymptotically stable. When
, the disease-free equilibrium point of model (1.2) is unstable.
Proof. According to the model (1.2), we take
. Thus, it can be seen that
(3.1)
Then, its Jacobi matrix of (3.1) at
is
The characteristic equation is
.
As for
,
. It is easy to know that one of the eigenvalues is
, rest up to
, take advantage of
,
,
, and
.
By the Hurwitz criterion, when
, all the eigenvalues are negative, the disease-free equilibrium is locally asymptotically stable. When
, the characteristic equation consists of one positive root and two negative roots, so the disease-free equilibrium is unstable, completing the proof.
Theorem 3.2.2. When
, model (1.2) has a globally asymptotically stable disease-free equilibrium point.
Proof. Now we use the next generation matrix method to prove this theorem. Establish
Because of
,
. If and only if
,
. So
. When
, model (3.1) satisfies
Le
, due to
we can prove
. From [24] we define a Lyapunov function as follows
, then the derivative of L can be written as
When
, the disease-free equilibrium is globally asymptotically stable.
3.3. Stability of Positive Equilibrium E*
Consider the differential equation
. Let
be the solution to this equation with the initial value
satisfying two hypotheses listed as follows [25].
(H1) There exists a compact attractive subset
,
(H2) Model (3.1) has a unique equilibrium
.
Lemma 3.3.1. [26] If
,
, and
, then all eigenvalues are negative real numbers.
Theorem 3.3.1 When
, the positive equilibrium point
is locally asymptotically stable.
Proof. The Jacobi matrix of model (3.1) at
is
Therefore
, take advantage of
, it is easy to derive
The determinant of
is
We can write
Among
. Calculate its determinant as
It’s made use of
. In conclusion, when
,
is locally asymptotic stability, the theorem is proven.
Lemma 3.3.2. [19] If the region D is simply connected and conditions (H1) and (H2) hold. When
, the only internal equilibrium solution
of the model
is globally asymptotically stable.
Since (H1) is equivalent to the consistent persistence of model (3.1) [26] and bounded in the feasible domain
. Then the consistent persistence of model (3.1) is equivalent to
being unstable [27]. According to Theorem 2.3.1, when
,
is unstable. So, the following lemma holds.
Lemma 3.3.3. When
, model (3.1) is consistent and persistent.
Theorem 3.3.2. When
, the positive equilibrium point
is globally asymptotically stable.
Proof. First, based on the
obtained above, the Lyapunov function is established as follows.
.
According to model (3.1), it can be concluded that
(3.2)
Then
The derivative of
along the positive solution of model (3.2) can be simplified as the following differential inequality
Obtained from model (3.1) that
and
, then
(3.3)
(3.4)
By using inequalities (3.3) and (3.4) we have
For satisfying that
(K is the inner compact attractive set
) is the solution of the model (3.1)
, there must be
Thereby
. Therefore, when
,
is globally asymptotically stable. The proof is now complete.
4. Numerical Simulation
In this section, the DED is cover simulation tool [28] [29] was used to numerically simulate 24 case data from 1998 to 2021, sensitivity analysis for
is conducted to reveal the influence degree on model outcomes. According to the assumption in reference [8], we obtain the basic regeneration number
where
,
, and
are the direct propagation rate, indirect propagation rate, and dropout rate, respectively. The biological meaning and the standard deviation of each parameters in model (1.2) are listed in Table 1.
Figure 1 illustrates the trend of cholera cases from 1998 to 2021 in China, indicating a decline in the transmission of this infectious disease. According to the simulation results, the transmission of cholera will eventually be gradually reduced and ultimately controlled.
In Figure 2, sensitivity analysis was applied. The basic reproduction number
of model (1.2) may determine the transmissibility, severity, and outcome of the pandemic. In order to seek for effective disease control measures, we therefore shall be concerned with the effects of input parameters
,
,
,
, on
. The results show that
,
,
and
are highly correlated with cholera infected persons. In order of relevance
,
,
,
. According to
Figure 1. Comparison of the reported cholera case data in China and the simulated solution
of model (1.2).
Figure 2. The PRCC values affecting the key parameters of
are obtained.
numerical simulation,
,
,
are positively proportional to I,
is negatively proportional to I. Undoubtedly, reducing the coefficient of disease transmission
and
, such as epidemic prevention propaganda, isolation, sterilization, and wearing masks can effectively control the spread of cholera. On the other hand, shortening the disease course of disease
can reduce the number of infected individuals. Therefore, it is possible for policy-makers to use multiple control measures jointly during the influenza pandemic.
5. Conclusion
Our study delves deep into the intricacies of the SIBR cholera transmission model, incorporating multiple modes of infection and a generalized incidence function. Initially, we derive the expression for the basic reproduction number. Subsequently, employing the Routh-Hurwitz condition and constructing the Lyapunov function, we establish a pivotal insight: when
, the disease-free equilibrium point is globally asymptotically stable. This implies that, absent any interventions, infectious diseases will eventually fade away. However, if
, we ascertain that the endemic equilibrium point becomes globally asymptotically stable, indicating the disease’s perpetual presence. Notably, we address and surmount the constraints posed by the existing literature [8], demonstrating that infectious diseases persist under specific conditions denoted by
. Furthermore, through meticulous numerical simulations, we elucidate the implications of the generalized incidence transmission model on the proliferation and containment of infectious diseases. These simulations form a theoretical foundation, enabling the evaluation of the efficacy of disease control measures. In essence, our analysis furnishes invaluable insights into the dynamics of the cholera transmission model, underscoring the criticality of implementing robust control strategies to thwart outbreaks and curtail the disease’s spread.
Acknowledgements
This work is supported partially by National Natural Science Foundation of China (Nos.12001178).