Implementation of an Agent-Based Model for Devil Facial Tumor Disease in Tasmanian Devils, and Evaluation of Interventions

Abstract

This thesis presents a geographical agent-based model to investigate different interventions that may be used to combat the spread of devil facial tumour disease (DFTD). DFTD is a clonally transmissible cancer that spreads as an allograft through bite wounds between Tasmanian devils [15]. The population of Tasmanian devils has been reduced by up to 90% since the first documented case of DFTD in 1996, and continued spread of DFTD threatens the survival of the species. The agent-based model presented here uses geographic data to simulate the devil maturation and mating, both spread and progress of DFTD, but also external pressures such as road kill, rodenticide, dog attacks, and generally lower survival in urban settings. Capturing these external pressures addresses a critical gap in current research which can highlight the importance of necessary interventions to preserve the species. Multiple interventions were investigated, including translocation of devils from a disease-free external population, translocation of devils from within Tasmania, use of an injection vaccine, and use of an oral bait vaccine. The injection vaccine increased the devil days lived (DDL) from the baseline of 6.81x10^8 to 7.76x10^8 and decreased the mean daily incidence of DFTD from the baseline of 52.43 to 39.27. Similarly, the oral bait vaccine intervention increased the DDL from 6.81x10^8 to 8.34x10^8, and decreased the mean daily incidence rate from 52.43 to 24.91, using the most aggressive distribution campaign. This oral bait vaccine campaign resulted in eradication of DFTD in the model. As the injection vaccine assumes an intensive trapping effort across the island, which can be very resource intensive, the more promising intervention is the oral bait vaccine due to its significantly lower resource investment and potential for disease eradication.