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Foot and Mouth Disease Modelling Projects
The Australian Government Department of Agriculture, Fisheries and Forestry (DAFF) is developing foot and mouth disease (FMD) simulation models that operate at a range of scales, including the farm level, the regional level and the national level.
Farm-level and windborne spread models
Farm level models are used to recreate within-herd or within-flock epidemic curves and to estimate daily virus production. These models tend to be mathematical and non-spatial, although spatial farm-level models have been developed for some of the extensive regional studies.
Farm-level models have also be combined with wind models to estimate the direction and magnitude of windborne spread of FMD virus. An example of this virus ‘plume’ is given in Figure 1 below.
Regional models
The bulk of DAFF modelling for FMD is based at the regional level. In this context, a ‘region’ denotes a part of Australia delimited by natural or geopolitical boundaries and characterised by reasonably homogenous animal production industries and systems. For a continent such as Australia, with diverse environmental and production systems, regions represent the most appropriate scale at which to assess control or eradication strategies.
DAFF has embarked on a structured program of regional modelling that will see detailed simulation and economic analyses carried out for each of 12 Australian agricultural regions (Figure 2). It is envisaged that the process will result in a suite of regionally-specific guides that can be used to assist with FMD planning or outbreak management.
Figure 2: the 12 Australian agricultural regions
To perform these detailed epidemiologic and economic analyses, DAFF uses a systematic three-step multi-model process. Under this process:
- The DAFF spatial model, AusSpread, is tailored to a regional setting and used to simulate the outbreak
- Outputs from the simulation are utilised by a dynamic bio-economic partial equilibrium model to estimate impact on Australian livestock industries and consumers; and
- Outputs from the partial equilibrium analysis are passed to AusRegion, the DAFF computable general equilibrium model, which estimates indirect impacts across the Australian economy.
The DAFF regional model, AusSpread, has been described by Garner and Beckett (2005). In brief, it is a stochastic spatial state-transition model (Figure 3) that has been developed specifically for regional simulation analysis.
Figure 3: the state transition model
AusSpread can use farm boundary or point location data as well as synthesised data based on agricultural statistics and land use information. The model is unusual in that it has been developed within a geographic information system (GIS) environment. This provides ready access to sophisticated spatial functions and mapping capabilities (Figure 4), and allows for easy incorporation of spatial data layers, such as roadways, waterways, urban centres and elevation.
Figure 4: AusSpread map outputs
The AusSpread model is considered a shell or tool that can be adapted to a wide range of regional applications. Adaptation in this sense includes alteration of interface elements, basal datasets, disease spread logic and model outputs. The approach is powerful as it allows the critical simulation elements to be retained without restricting the ability to tailor code to specific regional conditions.
National model
DAFF is in the process of entering into a collaborative arrangement with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), to develop and validate a whole-of-country model for FMD.
This project will rest on the preliminary development of a National Livestock Movement Model (NLMM). The NLMM will simulate livestock movements across the country based on data recorded from animal sales and from Australia’s National Livestock Identification System (NLIS). The model will incorporate information about seasonal and other trends in livestock marketing as well as information about prevailing regional meteorological conditions.
Using the NLMM, the national FMD model will simulate the likely distribution of infected animals and spread of disease up until the point of its first detection in Australia. From this point, relevant regional models will be invoked to provide more detailed simulations for regional disease spread and mitigation. The results of the simulation will be linked to Australian Bureau of Agricultural and Resource Economics (ABARE) partial and genera equilibrium models for detailed analysis of direct and indirect economic impacts.
The national FMD model and NLMM are due to be completed by end 2008.
Garner, MG and Beckett, SD (2005) - Modelling the spread of foot-and-mouth disease in Australia. Australian Veterinary Journal 83(12), 758-766.