Browsing by Author "Wang, Lin"

Now showing 1 - 5 of 5
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    Assessing oncolytic viral therapy and its barriers: a mathematical approach
    (University of New Brunswick, 2022) Jahedi, Sana; Watmough, James; Wang, Lin
    Oncolytic viral therapy is a targeted therapy in which natural or genetically modified viruses are used specifically to target cancer cells and not harm healthy cells. Despite some promising results in in vitro and in vivo studies of oncolytic viruses, many questions about treatment regimens and outcomes remain unanswered. Mathematical modelling can be helpful to shed light on understanding cancer cell dynamics and treatment outcomes. Firstly, we propose a set of ordinary differential equations that describes the interactions between cancer cells and free virus during oncolytic viral therapy. Then, using stability and sensitivity analyses, we seek to understand possible treatment outcomes. Then, by identifying thresholds for infection-related parameters such as the virulence level of the virus, the viral time scale and the infection transmission rate, we identify the type of virus that can lead to optimal treatment outcome. Some research suggests that a virus-specific immune response, such as one that becomes activated to prevent infection spread, may burden the success of oncolytic viral therapy. Extending our model, we propose models which include interactions between cancer cells, viruses, and antibody molecules/cytotoxic T cells during oncolytic viral therapy. We identify conditions under which each of the mentioned immune responses can be established by focusing on infection-related parameters. Our result shows virus-specific immune responses are not always detrimental: they can also be neutral or beneficial. Then by focusing on the virulence level of the free virus, we identify the extent to which the effect of a virus-specific immune response is detrimental and beneficial and show how the negative effect can be reduced or how beneficial results can be enhanced. Due to properties such as self-renewal and long-lasting quiescence, cancer stem cells are responsible for tumour recurrence and the failure of many conventional therapies. Here, we assess the efficacy of targeting cancer stem cells with oncolytic viruses. We show that targeting cancer stem cells does not always enhance the treatment efficacy, and optimal stem cell specificity depends on the rate of mitosis of infected cells. When infected cells are mitotic, the optimal result is obtained by perfect stem cell targeting.
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    Dynamics of a pathogen-immune interaction model
    (University of New Brunswick, 2013) Alshobrami, Norah; Wang, Lin; Watmough, James
    A new mathematical model is proposed to describe the interaction between the virus and the immune cells in an HIV infected host. For this new model, we study the existence of non-negative equilibria, bifurcation of equilibria, and stability of equilibria. We also carry out numerical simulations to illustrate all possible dynamics. In addition, we numerically explore drug therapy treatment strategies to find the right regimes for the strengths of the therapy and the duration of the treatment so that sustained immunity can be established.
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    Dynamics of Ecological Models with Intraguild Predation
    (University of New Brunswick, 2021-08) Ji, Juping; Wang, Lin
    This dissertation consists of five chapters. A literature review on intraguild predation models is given in Chapter 1. For the convenience of presentation, some basic concepts and results on dynamical systems are introduced in Chapter 1 as well. In Chapter 2, an intraguild predation model with a Beddington–DeAngelis functional response is investigated. The focus is on the existence, local and global stability of all feasible equilibria and uniform persistence of the model. Numerical simulations are performed to explore the influence of intraguild predator interference and intraguild predation on model dynamics. In Chapter 3, I develop a novel mathematical model that couples a competition model with an intraguild predation model via dispersal of intraguild prey driven by intraguild predator-avoidance. I show that large dispersal rate would lead to the collapse of species coexistence. In addition, I show that three modes of species coexistence are possible when the intraguild prey dispersal rate is not too large. An intraguild predation model with intraguild predator diffusion is proposed and studied in Chapter 4. It is shown that the local system can have four boundary equilibria and at most two interior equilibria. In my three-species intraguild predation model, only intraguild predator diffusion is considered. This results in a partially degenerate reaction-diffusion system. For this partially degenerate system, I show that the solution semiflow is bounded dissipative and the positive orbits of bounded sets are bounded. I also demonstrate that intraguild predator diffusion can lead to the occurrence of spatially nonhomogeneous oscillations and spatiotemporal chaos. Further, I show that intraguild predator diffusion can induce transitions between spatially homogeneous oscillations, spatially nonhomogeneous oscillations and chaos. Chapter 5 summarizes the main results of this dissertation and suggests some possible future work on intraguild predation models.
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    Dynamics of intraguild predation models
    (University of New Brunswick, 2014) Hu, Xi; Wang, Lin
    Intraguild predation combines two fundamental interactions between species: predation and competition, and is very common in nature. The intraguild predation module contains an intraguild predator, an intraguild prey and their shared resource. Both predation and competition occur between the intraguild predator and intraguild prey since the intraguild predator preys on the intraguild prey, and they both compete for their shared resource. It has been recognized that intraguild predation has significant impacts on the distribution, abundance, persistence and evolution of the species involved. In this dissertation, the dynamics of three intraguild predation models are investigated. I show that intraguild predation models can undergo a new global bifurcation, basin boundary bifurcation, and a torus bifurcation. I also show that the time delay in interguild predation models can induce stability switches and chaos. A review of the existing work on intraguild predation is given in Chapter 1. For convenience, some basic mathematical concepts and results on dynamic systems are also given in Chapter 1.
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    The effect of dispersal heterogeneity in bioinvasions
    (University of New Brunswick, 2016) Gharouni, Ali; Wang, Lin; Watmough, James
    The spread against a dominant flow of a marine invasive species with pelagic larval stage is a complex ecological phenomenon. This upstream spread involves the interplay between a number of processes including demography and dispersal of organisms, and variability in these processes. The main objectives of this thesis are to study the connection between dispersal, demography and spread in this setting and to understand the effect of variability in dispersal on spreading speeds. As a case study, I used the invasive green crab, Carcinus maenas, which has maintained a relatively consistent rate of spread for over 100 years covering a wide range of temperate latitudes and local hydrological environments along the Atlantic coast of North America. I developed a stage-structured integrodifference equation modelling framework to link spreading speed to underlying demographic and dispersal processes. First, simple kernels (namely Normal and Laplace) were used to model the larval dispersal. Then, a mechanistic kernel with behaviour was incorporated into the stage-structured integrodifference equation model. The temporal variability of the kernel was parameterized by using a particle-tracking submodel embedded into a 3-dimensional hydrodynamic model of the Gulf of St. Lawrence. Results indicated that the relationship between demography and dispersal was compensatory for all the three kernels. Sensitivity analysis indicated that larval dispersal had more effect on spreading speed than any demographic parameter. Our simulation implied that there was a spatial structure in the larval dispersal. Further, when dispersal parameters vary with time, using the time-averaged dispersal would underestimate the upstream invasion spread rates. Thus, accounting for spatial and annual variations in dispersal in population models is important to enhance understanding of spatial dynamics and population spread rates. My research thus contributed to (i) applied science by ranking different possible strategies in the management of a marine invasive species, (ii) theoretical ecology by developing tools to incorporate biophysical and behavioural features into the dispersal component of an integrodifference equation model, and by showing that the year-to-year dispersal variability increases the upstream spreading speed.