System Dynamics Analysis And Application Of The Spread Of Animal Diseases

System dynamics is to establish a dynamic model that evolves over time based on the internal operating causality of a complex system,and then analyze the macroscopic behavior and laws of the entire system.It has a wide range of applications in life sciences,social sciences,engineering sciences and other fields,and is the frontier of research in the world.This article focuses on the system propagation dynamics of animal diseases,and applies the theory and methods of system dynamics to the propagation of animal diseases,which is the intersection of system dynamics,epidemiology and human behavior research.We mainly conduct research on the spread of African swine fever in China,brucellosis,foot-and-mouth disease,prevention and control,and evaluation of intervention measures to provide theoretical support for animal disease control in my country.We build dynamic models of three types of infectious diseases,study the behavior of the models,explore the mechanism and development trend of disease transmission,propose corresponding control measures for infectious diseases,and evaluate the effectiveness of control measures for infectious diseases.The main research contents and innovations of the thesis are summarized as follows:(1)We established an evolutionary dynamic model of the interaction between the spread of African swine fever and live pig prices to assess the impact of African swine fever on live pig prices.Constructed a hexagonal spider web model of the relationship between the price of live pigs and the stock of live pigs,established a time-lag Logistics infectious disease model with price effects,the dynamic behavior of the model is analyzed,the basic regeneration number is calculated,the stability of the equilibrium point is studied,and the critical condition of the Hopf bifurcation is obtained.According to the data of live pig price,the data of live pig stock and the outbreak data of African swine fever,data fitting and parameter estimation are carried out to confirm the rationality of the model.Through sensitivity analysis,it visually demonstrated the impact of African swine fever on the price of live pigs and the number of live pigs,and assessed the key factors affecting the outbreak of African swine fever.The study found that the price of live pigs increases linearly with the basic reproductive number R0,and the number of infected pigs has a non-linear correlation with subsequent prices.(2)Asia type I foot and mouth disease vaccine quit risk assessment in China.Risk assessment of subtype I foot-and-mouth disease vaccine withdrawal.Through investigations on the prevalence of foot-and-mouth disease in China’s neighboring countries,Research on the distribution of wild animals in the surrounding area,Analysis of mixed grazing and import trade and smuggling of live animals and livestock products,we have established a foot-and-mouth disease transmission system dynamic model that includes risk factors to simulate the spread of subtype I foot-and-mouth disease in the farm.Under the mechanism of vaccine withdrawal,through data simulation,parameter estimation and basic regeneration number analysis.Through the calculation of probability indicators and loss indicators,the level of risk of foot-and-mouth disease in China is obtained.The conclusion reached is that the probability,time and scale of the national foot-and-mouth disease outbreak will be different if the vaccine withdrawal is implemented at different times.The later the vaccine is withdrawn,the smaller the probability of rebound.The probability of a rebound in inland areas is lower than that in border areas.(3)In order to study the optimal control strategy for the protection of breeders,we have established a system dynamics model for the spread of brucellosis in animal farms.The research analyzes the positive invariant set of the system,and calculates the analytical expression of the basic reproduction number.It also proves the global asymptotic stability and uniform persistence of the disease-free equilibrium point of the system,as well as the global asymptotic stability of the endemic equilibrium point and the existence of the optimal solution.It is concluded that the use of protective tools can reduce the transmission of brucellosis to farmers.