In 2008, the International Union for Conservation of Nature officially declared the Tasmanian devil an endangered species (http://www.iucnredlist.org/details/40540/0).
The animals were driven to extinction on the Australian mainland thousands of years ago, after humans introduced dingoes to the continent. The remainder of the wild population has since inhabited the Australian island-state of Tasmania. In the mid 1990's the population reached an estimated 150,000 devils.(1) Today, however, the animals are plagued by an infectious cancer known as Tasmanian devil facial tumor disease (DFTD). Since the emergence of the disease in 1996, the population has declined by more than 60%.(2) As a result, what was once the largest surviving population of marsupial carnivores is now threatened with extinction.
This type of cancer is very unusual. The great majority of cancer cases in humans and animals arise from a series of mutations in a single precursor cell and its daughter cells. The process occurs over a period of years and does not involve contact with any other individuals. DFTD develops differently. It's transmitted from animal to animal and the cancer cells themselves are the infectious agent.
Researchers describe this phenomenon as allograft transmission .(3) An allograft is the term for the transfer of cells/tissue from one individual to another. An example in humans is organ transplantation. The movement of cancer cells between animals has been confirmed by cellular and molecular studies. A normal devil cell contains 14 chromosomes.(3) DFTD tumor cells contain several very distinctive genetic changes and have only 13 chromosomes. Importantly, the tumors from every animal tested appear identical.(3) Researchers in Tasmania also found a devil with an unusual chromosomal abnormality in its non-tumorous tissue that did not appear in its tumor cells.(3) These findings strongly suggest that the cancer did not arise from the animals' own cells.
A cancer similar to DFTD occurs in dogs, and is known as Canine Transmissible Venereal Tumor (CTVT). The immune system of dogs is capable of overcoming the disease, but devils do not seem to be able to do so. Researchers have hypothesized that low genetic diversity among Tasmanian devils results in close kinship and reduces their immune responses.(4) (5) (6) (7) As a result, transplanted cancer cells are more likely to survive, grow, and spread.
Transmission can occur by biting, feeding on the same material, aggressive mating, and other social interactions. DFTD tumors mostly form on the face and/or in the oral cavity. The cancer can also metastasize to other areas of the body. Nearly 100% of infected devils die within 6 months of the onset of clinical signs.(3) Death results from an inability to feed, secondary infection, or symptoms associated with metastases.
If researchers are able to develop a vaccine for DFTD, it could halt disease spread significantly. Efforts are also being made to capture and relocate healthy animals to repopulate disease-free areas. The Tasmanian government is working with conservation specialists to reduce the impact of the disease.
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