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Derdei Bichara

Publications and source records attributed to Derdei Bichara.

10 recordsLinked to original sources
arXiv2018

Effects of migration on vector-borne diseases with forward and backward stage progression

Is it possible to break the host-vector chain of transmission when there is an influx of infectious hosts into a naïve population and competent vector? To address this question, a class of vector-borne disease models with an arbitrary number of infectious stages that account for immigration of infective individuals is formulated. The proposed model accounts for forward and backward progression, capturing the mitigation and aggravation to and from any stages of the infection, respectively. The model has a rich dynamic, which depends on the patterns of infected immigrant influx into the host population and connectivity of the transfer between infectious classes. We provide conditions under which the answer of the initial question is positive.

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arXiv2018

Global Analysis of Multi-Host and Multi-Vector Epidemic Models

We formulate a multi-group and multi-vector epidemic model in which hosts' dynamics is captured by staged-progression $SEIR$ framework and the dynamics of vectors is captured by an $SI$ framework. The proposed model describes the evolution of a class of zoonotic infections where the pathogen is shared by $m$ host species and transmitted by $p$ arthropod vector species. In each host, the infectious period is structured into $n$ stages with a corresponding infectiousness parameter to each vector species. We determine the basic reproduction number $\mathcal{R}_0^2(m,n,p)$ and investigate the dynamics of the systems when this threshold is less or greater than one. We show that the dynamics of the multi-host, multi-stage, and multi-vector system is completely determined by the basic reproduction number and the structure of the host-vector network configuration. Particularly, we prove that the disease-free \mbox{equilibrium} is globally asymptotically stable (GAS) whenever $\mathcal{R}_0^2(m,n,p)<1$, and a unique strongly endemic equilibrium exists and is GAS if $\mathcal{R}_0^2(m,n,p)>1$ and the host-vector configuration is irreducible. That is, either the disease dies out or persists in all hosts and all vector species.

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arXiv2017

Multi-Patch and Multi-Group Epidemic Models: A New Framework

We develop a multi-patch and multi-group model that captures the dynamics of an infectious disease when the host is structured into an arbitrary number of groups and interacts into an arbitrary number of patches where the infection takes place. In this framework, we model host mobility that depends on its epidemiological status, by a Lagrangian approach. This framework is applied to a general SEIRS model and the basic reproduction number $\mathcal{R_0}$ is derived. The effects of heterogeneity in groups, patches and mobility patterns on $\mathcal{R_0}$ and disease prevalence are explored. Our results show that for a fixed number of groups, the basic reproduction number increases with respect to the number of patches and the host mobility patterns. Moreover, when the mobility matrix of susceptible individuals is of rank one, the basic reproduction number is explicitly determined and was found to be independent of the latter. The cases where mobility matrices are of rank one capture important modeling scenarios. Additionally, we study the global analysis of equilibria for some special cases. Numerical simulations are carried out to showcase the ramifications of mobility pattern matrices on disease prevalence and basic reproduction number.

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arXiv2017

Vector-borne diseases models with residence times - a Lagrangian perspective

A multi-patch and multi-group modeling framework describing the dynamics of a class of diseases driven by the interactions between vectors and hosts structured by groups is formulated. Hosts' dispersal is modeled in terms of patch-residence times with the nonlinear dynamics taking into account the \textit{effective} patch-host size. The residence times basic reproduction number $\mathcal R_0$ is computed and shown to depend on the relative environmental risk of infection. The model is robust, that is, the disease free equilibrium is globally asymptotically stable (GAS) if $\mathcal R_0\leq1$ and a unique interior endemic equilibrium is shown to exist that is GAS whenever $\mathcal R_0>1$ whenever the configuration of host-vector interactions is irreducible. The effects of \textit{patchiness} and \textit{groupness}, a measure of host-vector heterogeneous structure, on the basic reproduction number $\mathcal R_0$, are explored. Numerical simulations are carried out to highlight the effects of residence times on disease prevalence.

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arXiv2016

Role of Mobility and Health Disparities on the Transmission Dynamics of Tuberculosis

The transmission dynamics of Tuberculosis (TB) involve complex epidemiological and socio-economical interactions between individuals living in highly distinct regional conditions. The level of exogenous reinfection and first time infection rates within high-incidence settings may influence the impact of control programs on TB prevalence. This study aims at enhancing the understanding of TB dynamics via the study of scenarios, within {\it simplified}, two patch, risk-defined environments, in the presence of short term mobility and variations in reinfection and infection rates. The modeling framework captures the role of individuals' `daily' dynamics within and between places of residency, work or business via the proportion of time spent in residence and as visitors to TB-risk environments (patches). As a result, the {\it effective population size} of Patch $i$ (home of $i$-residents) at time $t$ must account for visitors and residents of Patch $i$, at time $t$. The impact that {\it effective population size} and the distribution of {\it individuals' residence times} in different patches have on TB transmission and control are studied using selected scenarios where risk is defined by the estimated or perceive first time infection and/or exogenous re-infection rates. Our results suggest that, under certain conditions, allowing infected individuals to move from high to low TB prevalence areas (for example via the sharing of treatment and isolation facilities) may lead to a reduction in the total TB prevalence in the overall, here two-patch, population.

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arXiv2016

Role of short-term dispersal on the dynamics of Zika virus

In November 2015, El Salvador reported their first case of Zika virus (Zv) leading to an explosive outbreak that in just two months had over 6000 suspected cases. Many communities along with national agencies initiated the process to implement control measures that ranged from vector control and the use of repellents to the suggestion of avoiding pregnancies for two years, the latter one, in response to the growing number of microcephaly cases in Brazil. In our study, we explore the impact of short term mobility between two idealized interconnected communities where disparities and violence contribute to the Zv epidemic. Using a Lagrangian modeling approach in a two-patch setting, it is shown via simulations that short term mobility may be beneficial in the control of a Zv outbreak when risk is relative low and patch disparities are not too extreme. However, when the reproductive number is too high, there seems to be no benefits. This paper is dedicated to the inauguration of the Centro de Modelamiento Matemático Carlos Castillo-Chávez at Universidad Francisco Gavidia in San Salvador, El Salvador.

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arXiv2016

On the Dynamics of Dengue Virus type 2 with Residence Times and Vertical Transmission

A two-patch mathematical model of Dengue virus type 2 (DENV-2) that accounts for vectors' vertical transmission and between patches human dispersal is introduced. Dispersal is modeled via a Lagrangian approach. A host-patch residence-times basic reproduction number is derived and conditions under which the disease dies out or persists are established. Analytical and numerical results highlight the role of hosts' dispersal in mitigating or exacerbating disease dynamics. The framework is used to explore dengue dynamics using, as a starting point, the 2002 outbreak in the state of Colima, Mexico.

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arXiv2015

Assessing the Efficiency of \textit{Cordon Sanitaire} as a Control Strategy of Ebola

We formulate a two-patch mathematical model for Ebola Virus Disease dynamics in order to evaluate the effectiveness of \textit{cordons sanitaires}, mandatory movement restrictions between communities while exploring their role on disease dynamics and final epidemic size. Simulations show that severe restrictions in movement between high and low risk areas of closely linked communities may have a deleterious impact on the overall levels of infection in the total population.

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arXiv2015

SIS and SIR epidemic models under virtual dispersal

In this paper, we develop a multi-group epidemic framework via virtual dispersal where the risk of infection is a function of the residence time and local environmental risk. This novel approach eliminates the need to define and measure contact rates that are used in the traditional multi-group epidemic models with heterogeneous mixing. We apply this approach to a general $n$-patch SIS model whose basic reproduction number $\mathcal R_0 $ is computed as a function of a patch residence-times matrix $\mathbb P$. Our analysis implies that the resulting $n$-patch SIS model has robust dynamics when patches are strongly connected: there is a globally stable endemic equilibrium when $\mathcal R_0>1 $ while the disease free equilibrium is globally stable when $\mathcal R_0\leq1 $. Our further analysis indicates that the dispersal behavior described by the residence-times matrix $\mathbb P$ has profound effects on the disease dynamics at the single patch level with consequences that proper dispersal behavior along with the local environmental risk can either promote or eliminate the endemic in particular patches. Our work highlights the impact of residence times matrix if the patches are not strongly connected. Our framework can be generalized in other endemic and disease outbreak models. As an illustration, we apply our framework to a two-patch SIR single outbreak epidemic model where the process of disease invasion is connected to the final epidemic size relationship. We also explore the impact of disease prevalence driven decision using a phenomenological modeling approach in order to contrast the role of constant versus state dependent $\mathbb P$ on disease dynamics.

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