Threshold theory as a framework for understanding infectious disease dynamics in livestock populations: implications for the control of agriculturally important pathogens.

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The spread of agricultural infectious diseases has become a global problem. Disease outbreaks in economically valuable animal populations have important social, environmental and economic costs, erode consumer confidence in food products and present a risk to human health. Understanding infectious disease ecology is at the frontier of biological research, and a major long-term research question is: Under what circumstances can a pathogen invade and persist within a population? Mathematical modeling and computer simulation approaches have contributed to our understanding of disease dynamics and how best to intervene to prevent the introduction and spread of an infectious disease. Strategies for the control of select agricultural diseases, such as foot and mouth disease in cattle, have been investigated previously but important gaps remain. We are just beginning to understand the conditions that can lead to pathogen invasion and persistence in complex agricultural systems. Well-planned interventions could prevent or minimize these disruptive outbreaks however, the effectiveness and cost-effectiveness of novel strategies to prevent outbreaks is unknown. The proposed research program will remedy this knowledge gap by examining important challenges for our understanding of disease dynamics in livestock. We will develop agent-based, computer simulation models that facilitate the analysis of “what-if” scenarios to identify the most effective and cost-effective surveillance and control strategies. The models represent individuals within their simulated environment and their interactions, movements, decision-making, and related health states. We will use commercial swine farms and three swine pathogens as a model system for advancing our understanding of the factors controlling disease invasion and persistence, and how these factors interact to allow pathogens to persist. This proposal creates a platform for integrating data on swine pathogens into a unified modeling framework to develop a better understanding of the factors regulating disease introduction and spread within these populations. There is strong interest in linking infectious disease theory to policy. This program of research will highlight the ways in which swine producers can most effectively manage their animals in order to decrease the risk of pathogen invasion and persistence. Understanding the ways in which spatial structure, pathogen dynamics in the host and environmental variation can interact will allow us to identify the most effective and logistically feasible responses to the presence of these pathogens in swine under a variety of different management practices. Simulation models are a novel way to address our research questions and present rich opportunities for the natural sciences and engineering. Using simulation to address important agricultural diseases associated with food animals will open up new avenues for the application of these tools in the life sciences. Results obtained will provide health and economic benefits and strengthen existing public health planning and disease control strategies. Simulation allows us to optimize infection control practices so that we can allocate resources that are limited while at the same time minimizing disease transmission. Disease modeling is an important addition to the public health response and effective planning is the cornerstone of disease prevention.