MULTI-SPECIES MODELING OF ANIMAL MOVEMENTS AND TRANSBOUNDARY ANIMAL DISEASE OUTBREAKS IN THE U.S.

Transboundary animal diseases (TADs) are a major threat to the United States' (US) agricultural system, with the potential to affect food security and the US economy. Managing a TAD outbreak is complex; it must balance trade-offs among competing objectives, limited resources, and uncertainty in disease risk. Management will also depend on the livestock species(s) infected or at risk. Mathematical models are often used to understand potential outbreaks and response actions. Our goal is to develop data-driven, multi-species shipment and disease spread models for the US that can be used to anticipate the potential impacts of and response to TADs. FMD is a tier 1 TAD of concern for the US Department of Agriculture and can infect multiple species. In the US, the two largest livestock industries that could be affected by FMD are cattle and swine. In earlier work, we demonstrated the feasibility of data-driven, animal shipment models (US Animal Movement Model (USAMM)), despite the lack of a comprehensive shipment database, and developed relevant disease spread models for the US national scale (US Disease Outbreak Simulation (USDOS)). Our previous work addressed FMD outbreaks in cattle alone, but it is clear that swine would play a crucial role in a US FMD outbreak due to the large industry size, and significant transmission potential. Multi-species USAMM and USDOS will be robust and flexible tools that could be used with any other set of species and fast spreading livestock disease (e.g. ASF, highly pathogenic avian influenza, peste des petits ruminants virus), provided that demography, disease transmission parameters, and shipment networks are available.Objective 1: Develop multi-species USAMM. Since there is no federal database recording livestock shipments, modeling of diseases where transmission through animal shipments is important must rely on predictive tools. Currently, USAMM is the most comprehensive nationwide tool for the purpose and provides independent predictions for swine and cattle shipments at the national scale. However, several additional developments are required to provide more relevant predictions--for the scope of this application in particular and for livestock modeling in the US in general. Preliminary results from exploratory analyses suggest that shipment rates of swine are affected by the presence of cattle. Exploratory analyses also reveal pronounced effects of premises size in contact patterns that are not yet captured in the USAMM framework. Unless these issues are resolved, USAMM will have wide uncertainty in predictions regarding shipment patterns between areas dominated by one species or the other. Thus, in obj. 1, we will improve estimation of swine and cattle shipment contacts by improving the prediction of shipment rates in one species relative to premises locations of the other.Objective 2: Develop multi-species USDOS. USDOS is currently the only model running at the national scale for the US, capturing long range transmission via shipments, and is therefore invaluable for understanding potential TAD outbreaks. A critical piece of managing TAD outbreaks is planning and exploring options for diagnostics and control with accurate information regarding transmission, resources, and potential targets. Therefore, in order to investigate diagnostic and control strategies for potential multi-species FMD and other TAD outbreaks in the US, modeling tools must include species-specific targeting and prioritization for diagnostic and control actions, and the respective resource constraints. In obj. 2, we will develop species specificity in both diagnostics and control in the USDOS model and expand disease transmission to allow for multiple species. This functionality will increase USDOS flexibility and facilitate more realistic transmission scenarios and multi-species response actions.Objective 3: Evaluate multi-species FMD outbreak dynamics, and response strategies in the US. TADs include both single and multi-host pathogens. Because FMD has the potential to behave as a single species or a multi-species outbreak, it provides a unique study system to explore the differences between intra- and cross-species transmission dynamics, and how species involvement changes management needs. FMD outbreaks are also suspected to have begun in different species, with cattle and swine being the first and second most commonly first suspected species, respectively. Understanding the potential multi-species outbreak trajectories when infection begins in cattle versus swine--including the impact of diagnostic testing and control on these trajectories--will help to mitigate potential outbreak impacts on US agriculture business continuity, competitiveness and food safety. We will use multi-species USDOS (obj. 2) with multi-species USAMM (obj. 1) to explore the spatial spread of multi-species FMD outbreaks when introduced into cattle and swine, respectively, and species-specific diagnostic testing and control scenarios, targeting one or both of the species involved.