Assessment of the Efficiency of Vaccination and Short-term Isolation in Lowering the Disease Load in Koalas...

Koala populations in some regions of eastern Australia are in critical condition. Our research aims to develop effective conservation strategies for these declining koalas threatened by chlamydia infection, predation, and climate change. To achieve this, we developed a mathematical model that includes populations of dingoes and koalas categorized as susceptible, infected, and confined. We conducted a bifurcation analysis within the ordinary differential equations (ODE) model to explore the occurrence of a Hopf bifurcation. This analysis aimed to identify conditions under which the system undergoes qualitative changes in its dynamics, specifically transitions from stable equilibrium points to periodic oscillations. By examining how the system's behavior shifts as parameters are varied, we could determine the thresholds at which these bifurcations occur, providing insights into the potential for oscillatory patterns in koala populations and disease dynamics. Additionally, we performed a global sensitivity analysis using the partial rank correlation coefficient (PRCC) method. This approach helped us evaluate the relative importance of different parameters on disease prevalence and koala mortality. Extensive numerical simulations allowed us to compare the outcomes of deterministic, stochastic, and diffusive models. Our research indicates that the survival of koala populations is significantly influenced by several key factors: the presence of dingoes, vaccination efforts, and temporary quarantining. Simulations of spatially explicit systems show that increased diffusion among dingoes leads to a more significant clustering of the infected koala population. Our study offers theoretical evidence that vaccination and temporary isolation strategies can significantly improve health outcomes for koalas infected with Chlamydia.