banner by Meghan Carlton and Daniel Walsh 

Tasmanian Devils: Face to Face with Extinction

by Peter Allen

The Tasmanian devil is a marsupial largely irrelevant to the Western world. The only representation the furry creatures have gotten in American culture has been that of Taz, an iconic, rambunctious character on “Looney Tunes.” Taz was built not only physically in the image of the Tasmanian devils, but behaviorally as well. His signature tornado-like devouring of anything in his path was inspired by the devil’s rapid and ferocious eating habits and overactive use of biting in everyday life. Tasmanian devils are largely isolated creatures, but upon any encounter with another of its kind, be it to eat, mate or dispute territory, the devil uses its mouth as its greatest weapon.  It may be hard to sympathize with such barbaric creatures, but in the past two decades, this behavior has been the main vector of a transmissible cancer that has caused an astounding 80 percent decline in the overall population of the species.

Somewhere in recent history, a single devil developed tumors that spread to its face. Considering Tasmanian devils naturally communicate by biting each other’s faces, this single devil’s cancer has led to every other detected case. We know this because cancer cells taken from several different locations across Tasmania, an island off of Australia where these animals are found, have not only proven to be genetically different from their hosts, but also all identical to one another.

This form of cancer does not act like the cervical cancer caused by HPV or other strains that rely on a virus to pass from one creature to another, but rather by allogeneic transfer. In this process, whole cells of one individual are directly transferred to another unrelated individual. If this was the whole story, then certainly more kinds of cancer would be transmissible. Instead, it is the Tasmanian devil’s rampant inbreeding that disarms the otherwise effective branches of its immune system.

Devils are believed to have been hunted to extinction on the mainland of Australia. With the added effects of climate change and deforestation, different devil populations became more and more isolated on the island of Tasmania. Inbreeding led to a lack of genetic diversity, and now upon contact, one devil’s immune system cannot distinguish foreign cancer cells from its own. When these tumors are allowed to grow, they have a near 100 percent fatality rate. They become so large that they physically disarm a devil’s ability to eat and drink, leaving it to die by starvation. In some cases, these tumors have also been found to lead to dissolving of the skull, as well as organ failure. The most common location for the development of these tumors has earned the illness a fitting name: Devil Facial Tumor Disease (DFTD).

Transmissible cancer is a horrifying concept. In its non-transmissible forms, the disease is already our nation's second leading cause of death, with nearly 600,000 recorded deaths each year. However, fear not, because as of today there are only four recorded kinds of transmissible cancer, and none of them occur in human populations. Besides that of the Tasmanian devil, there have also been documented cases of transmissible leukemia in clam populations and venereal tumors in dogs that both spread by allogeneic transfer like DFTD. In addition, certain hamster species have been riddled with a kind of cancer that is propagated through allogeneic transfer as well, but rather than spreading directly from one hamster to another, whole cancer cells are transmitted via mosquitoes. All these cancer lines would be marked as foreign by a properly functioning human immune system and would be terminated prior to causing any harm. So, in its current forms, infectious cancer is not something we have to worry about.

Although there are only a handful of different transmissible cancers that have been discovered, a recent study has marked the emergence of a new kind among devil populations. These cells have a genetic makeup that is different from the previous cell line, signifying the separate development of a second form of transmissible cancer in devils. This occurrence could be evidence that transmissible cancers are arising more commonly than we previously thought. Although this does not necessarily translate into human risk for developing such forms of cancer, it does further enforce its importance as something to keep an eye on.

We may not need to worry about contracting the devil’s cancer, but the loss of these creatures would be truly detrimental. The devil is Tasmania’s largest extant marsupial carnivore and in that role it keeps fox and feral cat populations in check. Areas with a great decrease in the number of devils have already seen a growth in these populations, which, if not lowered, have the potential to wreak havoc on the rest of Tasmania’s wild fauna. Feral cats have been shown to spread toxoplasmosis, the ingestion of which leads to infection in native mammals, livestock and humans, particularly with exposure in the womb. Tasmania’s Department of Primary Industry, Parks, Water and Environment has already begun to note an increase in the number of sheep samples testing positive for this disease. Beyond the collective trauma the devils’ absence could cause for Tasmania’s farming and wildlife, the creature plays an important role in the Tasmanian psyche, and possibly more than anything else, they are an icon of wild Tasmania. The devil is a source of inspiration, culture and ecological balance, the loss of which would be felt for years to come. To prevent this from happening, we have been focusing our efforts on salvaging what remains of the creature’s population.

DFTD has been wreaking havoc for nearly two decades, but it was only in 2003 that the Save the Tasmanian Devil Program (STDP) was put into place by the Australian and Tasmanian governments. In the past 13 years, the program has successfully established an “insurance population” of uninfected individuals and walled off isolated habitats from any chance of contact with diseased populations. After salvaging and protecting these remaining untouched populations, the STDP shifted its focus to reestablishing significant populations in areas previously ravaged by the disease. One example of this took place in 2012 when the program began depopulating the Forestier Peninsula in southeast Tasmania by capturing all devils. By 2015, researchers were certain that the region was disease-free and after putting up barriers to ensure DFTD would not spread back into the region, 39 devils were released there, some of which were direct descendants of those extracted in the first place. Furthermore, researchers are delving deeper into the nature of the disease, with the hope of ultimately creating a vaccine that can work in the wild.

On that front, scientists at the University of Tasmania’s Menzies Institute for Medical Research have recently found breakthrough success in overcoming the cancer cell’s ability to stay under the immune system’s radar due to inbreeding. “By treating these [cancer] cells with special proteins,” Professor Greg Woods remarks in a video on the STDP website, “they then become visible to the devil’s immune system and when we immunize the devils, it produces an immune response.” These proteins work by flagging the cells as foreign, thereby marking them to be terminated by the devil’s immune system.

While promising, the vaccine has so far only proven to work in the laboratory. A clinical trial involving a group of treated devils has just been released to join an infected population. The results of this clinical trial will give us a major indication of how quickly, if at all, the devil populations will bounce back if the treatment is successful in the wild. Regardless, these breakthroughs continue to bring hope in the devils’ fight against DFTD.

In the case of DFTD, we find examples of evolution right before our eyes. A species knocked to the brink of extinction by its own habits still has a chance of survival. It is unclear whether the devil populations would have enough individuals left after the disease ran its course to properly repopulate, but truthfully it is rather unlikely. Without the intervention of human conservation efforts, this iconic species would most likely have been lost to the annals of time.