Tasmanian devils are unique marsupials native to the island of Tasmania, recognized for their powerful jaws and distinctive calls. These carnivorous animals now face a grave threat from Devil Facial Tumor Disease (DFTD), a fatal and unusual transmissible cancer. The disease manifests as visible tumors, primarily around the face and neck, leading to severe health complications and threatening the species’ long-term survival.
The Emergence of a Unique Cancer
Devil Facial Tumor Disease was first observed in 1996 in northeastern Tasmania. Scientific analysis confirmed the disease originated from a single cancerous cell line, meaning it developed in one individual devil. Genetic studies revealed the original tumor cells were derived from a Schwann cell, a type of cell that supports nerves.
All subsequent tumors of this primary strain, now known as DFT1, are direct descendants of that initial cancerous cell. An independent second strain, DFT2, was identified in 2014 in southern Tasmania, also originating from Schwann cells but from a different devil. The discovery of these distinct, clonally transmissible cancers was a significant event in wildlife disease.
A Contagious Cancer’s Biology
DFTD is unusual because its cancer cells can transfer directly between individuals, acting as an allograft, or transplanted tissue. The host devil’s immune system fails to recognize and reject these foreign cancer cells. This immune evasion occurs primarily because tumor cells lose or significantly reduce the expression of Major Histocompatibility Complex (MHC) class I molecules on their surface.
MHC molecules present foreign elements to the immune system, triggering a defensive response. The low genetic diversity within Tasmanian devil populations, especially concerning their MHC genes, contributes to the disease’s success. This genetic similarity makes it harder for their immune systems to distinguish between their own cells and the foreign tumor cells.
How the Disease Spreads
The primary method of DFTD transmission between Tasmanian devils is direct physical contact. This often occurs during aggressive social behaviors like biting. Devils frequently engage in fights over food, during mating rituals, or other social interactions, creating opportunities for tumor cell exchange.
When an infected devil bites another, or when tumor cells contact an open wound, live cancer cells can transfer. Less common routes of transmission include ingesting infected carcasses. This allows the disease to spread efficiently through devil populations.
Impact on Tasmanian Devil Populations
Devil Facial Tumor Disease has caused severe declines in Tasmanian devil populations across their native range. The wild devil population has plummeted by an estimated 80%, with localized areas experiencing declines up to 90-95%. The tumors interfere with essential functions like feeding and vision, leading to starvation and death within three to nine months of visible symptoms.
The disease has also significantly altered the age structure of devil populations, with fewer mature breeding individuals surviving. Due to these declines, the Tasmanian devil is now officially listed as an endangered species by the International Union for Conservation of Nature (IUCN). The disease has spread to affect more than 90% of the species’ geographic distribution across Tasmania.
Conservation Efforts
Numerous strategies are underway to protect Tasmanian devils from DFTD. A central effort involves establishing “insurance populations” in captive breeding programs and on isolated islands. These populations are carefully managed to maintain genetic diversity, providing a safeguard against the disease’s impact in the wild.
Scientific research continues to investigate potential genetic resistance in some devils and to develop a vaccine. Early vaccine trials have shown promise in stimulating an immune response against the cancer cells. Active management of wild populations also includes ongoing monitoring and protecting currently disease-free devil groups.