Tasmanian devil (Sarcophilus harrisii)
- Listed as endangered by the IUCN
The Tasmanian devil is a creature faced with extinction, the victim of a gruesome facial cancer, known as the devil face tumor disease (DFTD). The disease causes tumors to form in and around the mouth, interfering with feeding and eventually leading to death typically by starvation.
Cutting edge genetic sequencing of these carnivorous marsupials has revealed that humans had a hand in their decline: centuries of human persecution left the devils stripped of genetic diversity and vulnerable to disease.
Due to low genetic diversity, when the transmissible cancer (DFTD) appeared in 1996 it rapidly spread through most of Tasmania. The disease is transmitted by physical contact, mostly facial biting during sex. It is almost always fatal, usually within a few months of clinical expression. As a result, the Tasmanian devil population has declined precipitously during the last few decades.
Due to the species’ sharp decline, the International Union for the Conservation of Nature (IUCN) has classed it as endangered. Studies estimate that without effective application of conservation measures the species could be wiped out within two to three decades.
Involved from 2008 – 2012
Principal investigator, Dr. Greg Woods (Menzies Research Institute, Hobart, Tasmania) received $50,000 in funding from the Turner Foundation, Inc. (TFI) (as recommended by the Turner Endangered Species Fund) to implement a study to determine if any Tasmanian devils in West Pencil Pine (western Tasmania) were naturally immune to DFTD.
Project Goals & Objectives
Devil Facial Tumor Disease (DFTD) is a transmissible cancer that has killed approximately 80% of the wild Tasmanian devil population. The IUCN Red List of Threatened Species now lists the Tasmanian devil as ‘Endangered’. The spread of the disease continues to occur into northwestern Tasmania, where the remaining disease‐free population is located. Survival in the wild depends on either natural (e.g. genetic) or induced (e.g. vaccine) resistance. In an area of Western Tasmania (West Pencil Pine), there was hope that some devils might have some level of natural resistance to DFTD. This area was continually monitored by trapping devils and obtaining blood samples.
TFI’s grant, provided via the University of Tasmania Foundation USA and the “Save the Tasmanian Devil Program Appeal”, was directed towards determining if any Tasmanian devils in West Pencil Pine were immune to DFTD. It was first necessary to develop a diagnostic test that could identify evidence of an immune response against the DFTD cancer cells. Once this was achieved the test was then used to analyze the blood samples of Tasmanian devils from West Pencil Pine.
TFI’s grant facilitated several significant breakthroughs.
1. Development of a sensitive diagnostic test (Enzyme Linked Immunoassay; ELISA) to identify potentially resistant devils. This test is now in continual used in research to screen blood samples of Tasmanian devils for evidence of immunity to DFTD.
2. Hundreds of different blood samples from 40 Tasmanian devils in West Pencil Pine were analysed and there was evidence for some level of immunity to DFTD in five of these devils. This evidence confirmed that some Tasmanian devils can produce an immune response against the DFTD cancer cells. However, even though an immune response was identified, it did not always protect the devil from DFTD. Furthermore, the number of devils with natural protective immunity was too low to be effective.
Through collaborative studies (which incorporated support from the Turner grant) the following was also accomplished the following:
1. Identified that DFTD is a cancer of Schwann cells (specialized cells associated with the nervous system)
2. Determined that immune cells (Natural Killer cells) of Tasmanian devils have the ability to kill cancer cells
Several key results have been obtained since completion of the TFI grant in 2010.
Through endeavors to produce a sensitive test to determine whether wild Tasmanian devils can produce a response to DFTD, researchers developed important international collaborations that are resulting in the development of more specific laboratory reagents. These will be used to develop a range of important bioassays for monitoring devils in the wild.
Researchers discovered that immune cells (Natural Killer cells) can be activated in vitro to kill DFTD cancer cells. The importance of this discovery is that DFTD cancer cells can be made susceptible to the devil’s immune system and a vaccine to protect against DFTD is possible.
Researchers determined that a lack of genetic diversity does not explain why DFTD cancer cells can be transmitted between devils without inducing an immune response.
Researchers ascertained that DFTD cancer cells can be transmitted between unrelated devils because they fail to express important immune recognition genes, such as MHC.
In April 2012, conservation biologists successfully treated a DFTD diseased Tasmanian devil. The DFTD tumor in this devil was the size of a golf ball and treatment of this devil with immunotherapy resulted in a complete regression of the tumor. This is the first evidence for the possibility of a successful cure.
These encouraging results, facilitated by the TFI grant with oversight by the TESF, justifies optimism that, with sufficient resources, a vaccine and immunotherapy treatment is achievable to protect the Tasmanian devil from extinction in the wild.
Devil Facial Tumor Disease has devastated the devil population and the species now faces extinction. No natural resistance has been found in the affected population, but recently an area of Western Tasmania (West Pencil Pine) has been identified where the disease is not spreading as rapidly as would be expected. The devils in this area have a slightly different genetic makeup to devils in the east of Tasmania where the disease has spread rapidly throughout the population. The area of West Pencil Pine offers hope that some devils may have some level of natural resistance to DFTD. This area was continually monitored by trapping the devils and taking repeated blood samples from individual devils which were then analysed to determine if there was any evidence of an immune response to DFTD. Forty devils were trapped on at least five occasions and blood samples from these devils were analysed. Of these 40 devils, there were five devils that had evidence for anti-DFTD antibodies. This suggests that these five devils had been exposed to DFTD and their immune response was activated and therefore they were protected against the disease. This is encouraging evidence that there are some devils that can produce an immune response against DFTD.
The best possible scenario for the survival of the Tasmanian devil is the existence of devils that can naturally respond to DFTD. Such “DFTD-resistant individuals” would have a natural immune response and this could be detected in recently exposed devils by the presence of antibodies to DFTD in their serum. Consequently, the major objective of the project was to identify devils that might be genetically resistant to DFTD.
The first aim of this proposal was to identify DFTD-specific tumor antigens. The second aim was to develop a technique that could be used to screen as many devils as possible for evidence for an immune response against DFTD. The third aim was to screen Tasmanian devils from the area of West Pencil Pine, as this area is where the disease is not spreading as rapidly as other areas and there is evidence for a difference in the genetics of some animals in this population. The fourth aim was to determine whether devils could produce an immune response against DFTD.