Study On The Transmission And Evolutionary Dynamics Model Of Toxoplasmosis

Toxoplasmosis is a life-threaten zoonosis, whose transmission and evolutionary dynamic processes involve complex and representative biological characteristics. In order to deepen the understanding of the transmission and evolutionary mechanism of toxoplasmosis, this thesis analyze the transmission of the disease between hosts in depth and make the first attempt to investigate the evolutionary dynamics of the virulence of Toxoplasma gondii(T. gondii) strains.Firstly, Latin hypercube sampling method is adopted to make the sensitivity analysis on the parameters associated with the transmission of toxoplasmosis, and the key factors which affect the transmission processes. Based on those results and with insensitive parameters to the environmental infection risk excluded out, a simplified agent-based model for the transmission dynamics of toxoplasmosis has been built up.Secondly, a differential equation model of the transmission dynamics of toxoplasmosis corresponding to above simplified agent-based model is set up. The parameters in these equations are identified by multiple shooting method and the relations between the infection probability and the virulence of T. gondii strain is built up. The amounts of infected hosts calculated by the above differential equation model with identified parameters agree well with those obtained from the simplified agent-based model, which confirms the reasonableness of this differential equation model.Finally, an adaptive dynamic framework on the evolution of the virulence of T. gondii strain is built up and the evolutionary scenarios of T. gondii are discussed. The conditions of the occurrences of convergence stable singularities, repellers and bifurcation points during the invasion process have been delineated and the evolutionary scenario after bifurcation is described. Those investigations indicate that the regional distribution of T. gondii is inherently associated with its dominant transmission routes in those places.By combining the transmission and evolutionary dynamics model of toxoplasmosis established in this thesis with the within host dynamics model of T. gondii, one can obtain a complete transmission and evolutionary dynamic calculation and analysis framework of toxoplasmosis and provide a theoretical basis for the prediction and control of toxoplasmosis.