Devil Facial Tumor Disease (DFTD) is a devastating, transmissible cancer threatening the survival of the Tasmanian devil, the world’s largest carnivorous marsupial. First observed in 1996, DFTD has since swept across the island state of Tasmania, causing catastrophic population declines. The rapid and near-universal lethality of the disease has led to an estimated loss of over 70 to 80 percent of the wild devil population.
The Physical Effects of Devil Facial Tumor Disease
The first visible signs of Devil Facial Tumor Disease are small lesions or lumps that appear in and around the mouth and face of the infected animal. These initial nodules rapidly grow into large, disfiguring tumors that often ulcerate and can invade surrounding tissues of the neck and head. The cancer is transmitted primarily through biting, a common social behavior among devils during mating and feeding, which directly transfers living tumor cells into open wounds.
The tumor growth inside the mouth can become so extensive that it pushes out teeth, severely hindering the devil’s ability to eat. Most infected devils die within three to nine months of the tumors becoming visible, succumbing either to starvation or secondary infections from the open, festering lesions.
The disease’s high mortality rate has profoundly altered the demographic structure of wild populations. In areas where DFTD is established, nearly all sexually mature devils become infected, resulting in a loss of older age classes. This forces devils to breed at a younger age, sometimes as one-year-olds, which disrupts the natural life cycle and limits the number of breeding events a female can complete. Only a few isolated, disease-free populations remain in the remote western and southwestern parts of the island.
The Unique Biology of Contagious Cancer
Devil Facial Tumor Disease is unique because the cancer itself is the infectious agent, spreading as an allograft—a transplant of foreign cells—from one animal to another. The tumor cells originated from a Schwann cell—a type of cell that insulates nerves—in a single devil, and have since become a clonal lineage that survives across multiple host animals.
Researchers focused on how the transferred tumor cells evade the recipient devil’s immune system. The cancer cells employ immune masking by failing to express Major Histocompatibility Complex (MHC) molecules on their surface. MHC molecules are cell surface proteins that act as identity tags, presenting internal antigens to the immune system’s T-cells to signal whether a cell is “self” or “non-self.”
By silencing the genes responsible for producing these MHC markers, the DFTD cells essentially become invisible to the devil’s immune surveillance. This evasion is compounded by the already low genetic diversity within the Tasmanian devil population, particularly in the genes controlling the immune system.
Two distinct transmissible cancer strains are known to affect the species, highlighting the devil’s unique susceptibility. Devil Facial Tumor 1 (DFT1) is the original, widespread strain that has devastated populations across the state. A second, genetically separate strain, Devil Facial Tumor 2 (DFT2), was discovered in 2014 and appears to be confined to a peninsula in southeastern Tasmania. Both strains independently arose from Schwann cells, suggesting a specific biological predisposition within the species to this unusual form of malignancy.
Current Conservation Strategies
A comprehensive conservation program has been created to protect the remaining devils and eventually reintroduce disease-free individuals to the wild. One of the most significant efforts involves establishing “insurance populations” of healthy devils in captive breeding facilities across Australia and in isolated, disease-free habitats. These populations are meticulously managed to maintain maximum genetic diversity, ensuring the species retains the necessary variation to adapt to future threats.
Maria Island, a large, offshore island, serves as a natural sanctuary where devils are protected from the disease. Researchers carefully manage the genetics of this population by using pedigree analysis and genetic markers to guide breeding pairs and prevent inbreeding.
Current research also focuses on understanding and leveraging the devils’ natural immune response to the cancer. Scientists have observed a small number of wild devils that demonstrate tumor regression, suggesting they are developing a form of natural resistance. This discovery has led to genetic studies identifying specific genes associated with this resistance, with the hope of selectively breeding devils with enhanced immune capabilities.
The development of a vaccine or immunotherapy treatment is a major goal for long-term management of the disease. Experimental treatments have shown that stimulating the devils’ immune systems, sometimes by using immune-boosting drugs to force the tumor cells to display MHC markers, can induce a rejection response. If successful, a vaccine would allow for the managed reintroduction of resistant devils into the wild, offering the most promising path toward stabilizing the species’ population numbers.