Infectious diseases pose increasing threats to endangered species. Few tools, however, are available to manage such diseases in free-ranging populations. Tasmanian Devil Facial Tumor Disease (DFTD) threatens the largest surviving marsupial carnivore, Sarcophilus harrisii, with extinction. The disease was first detected in 1996, and has now spread across almost the entire island of Tasmania, which is the sole native range of the species. Populations of the Tasmanian Devil have decreased by 95% in affected areas, although no population has yet totally disappeared. This is a highly unusual infectious disease, being a directly transmitted infectious cell line. Nevertheless, attempts to understand and manage DFTD have important lessons for ecologists dealing with emerging infectious disease threats to wildlife.
Results/Conclusions
The initial management action was to establish captive, disease free insurance populations on the Australian mainland, where they are not exposed to infection from wild devils. This has been successfully accomplished, but this strategy clearly cannot, in itself, maintain wild free-ranging populations in their native range. An attempt to eliminate disease from a semi-isolated peninsula by culling diseased animals was unsucessful, and subsequent modeling showed that no feasible culling strategy was able to eradicate disease whilst maintaining the devil population. Physical barriers to isolated disease-free populations were considered, but rejected as impractical. Research to investigate a vaccine is in progress, but no vaccine has yet been shown to be effective. The best prospect for managing this disease in the wild is thus likely to be accelerating the coevolution of both host and disease. We present evidence of genetic change within both the devil and the tumor population, and use novel intergral projection models to investigate the consequences for the viability of Tasmanian Devil populations. Whilst both the empirical work and the modeling are not at the stage where we can definitively conclude that devil populations will recover, we can identify the extent of increased resistance or tolerance that would be required for population recovery.