Thesis

Modeling the impact of host-vector interactions on pathogen transmission between hosts

Plant disease is often transmitted among plants by an infectious agent called a vector during the process of vector feeding on plants. As a result of insect feeding without a pathogen, there are already interactions between plants and vectors, which have a variety of effects, including a reduction in nutrient acquisition and vector fitness, and an increase in vector movement, etc. Most of these interactions are considered as the vector-induced host defensive responses against the vectors. We investigate how such responses affect the spread of a vector-borne pathogen in the host population, using compartmental models. We incorporate the responses into the model by introducing separate compartments for vector-susceptible and vector-refractory plant hosts. A feeding model and an epidemic model are presented along with a stability analysis. The full model is developed as a combination of these two models. A stability analysis is performed along with a thorough sensitivity analysis to investigate the effects of vector-induced host responses on disease spread. Numerical simulations are performed to verify the results found in the stability and sensitivity analyses. The sensitivity analysis indicates that vector-induced defensive host responses are important factors impacting the spread of a pathogen in a plant disease system. Changes in feeding rates have a substantial effect, positively correlating with the disease spread. Changes in transmission probabilities also have a significant impact; a lowered transmission probability corresponds to a slower pathogen spread. The proportion of vector refractory hosts in a population at the onset of a disease is also essential to influence pathogen spread; a higher percentage of vector refractory hosts leads to a lower growth rate of the pathogen in the system. Such a finding implies that allowing vectors to feed and remain on uninfected plant hosts potentially slows down the disease spread. Therefore, it is practically advisable not to completely remove the insect population from host plants to prevent disease spread.

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