Managing a fatal infectious cancer in a threatened species: Tasmanian Devil Facial Tumor Disease

As the largest surviving marsupial carnivore, the Tasmanian devil is an iconic species.  A disfiguring and invariably fatal facial cancer, first reported in 1996, has now spread across most of the range of the devil, leading to population declines of up to 90% and a prognosis of likely extinction in 15-20 years. Transmission experiments have confirmed that the cancer is infectious and genetic evidence strongly suggests that it is a transmissible cell line.  Based on this problem, we present a decision tree for handling emerging diseases in wildlife, emphasising steps that should be taken before the disease can be identified and a vaccine or treatment can be developed. Captive “insurance” populations have already been established and establishing free-ranging disease-free populations on offshore islands is now being investigated.  A disease suppression trial, in which all infected animals captured are removed, is in progress on a large peninsula that is connected to the main island of Tasmania only by a single bridge.  Results to date show that the removal program has influenced the progression of the tumor epidemic. The stage structure of the tumor population has changed, with fewer large tumors now being found. In diseased populations without disease suppression, very few individuals older than 2 years are captured, whereas in this manipulated population, the age structure is similar to that of undiseased populations.  It appears that that the rate of geographic spread of the disease has been slowed, although whether eradication can be achieved remains uncertain. We present a model structure to evaluate the effectiveness of this removal program.