Decision Support Tools for Vector-borne Spread of Animal Disease

Bluetongue is a vector-borne, viral disease of ruminants that can cause substantial losses in productivity in farmed livestock. It is transmitted by Culicoides midges (Diptera: Ceratopogonidae) which means that the geographic distribution of disease is restricted to those regions where these vectors are present. In 2006 a virulent serotype of bluetongue (BTV-8) was detected in Northern Europe causing losses of livestock with knock-on economic and welfare effects. Bluetongue virus is endemic in Northern Australia, but clinical signs of disease have not been reported in either cattle or sheep. The risk of incursion of a virulent strain of bluetongue into Australia represents a constant threat, particularly the risk imposed by infected Culicoides midges blown from Indonesia to the northern borders of the Northern Territory. This thesis reports the results of a series of studies designed to enhance Australia’s preparedness for an incursion of a virulent serotype of bluetongue. This objective was achieved by design and implementation of facilities to allow the Australian Animal Disease Simulation model (AADIS) to simulate the spread of vector-borne diseases. In Chapter 3 we developed a model to allow the spatial and temporal distribution of Culicoides spp. across Australia to be estimated as a function of ambient temperature, prevailing wind conditions and the presence of cattle. In Chapter 4 a model of bluetongue virus vector-host transmission was developed, using the simulated midge population from Chapter 3 for the source population of insect vectors and details from the National Livestock Identification Scheme for the cattle host population at risk. A novel approach in Chapter 4 was the separation of host and vector populations into two ‘layers’ of different spatial format: a raster layer for the insect vector population and a spatial vector layer (i.e. points) to represent the cattle herd population at risk. This allowed our model to be readily adapted for other ins