The Devil We Know and the One We Don’t: The Tasmanian Devil, Face Cancer, and a Strikingly Similar Future for Humans and Marsupials Alike

After decades of devastating population declines due to cancer, the Tasmanian Devil evolves to combat it before our very eyes.

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Meg Jerrard / Unsplash

A Tasmanian Devil smiles for the camera.

Confined to the island of Tasmania, just south of Australia, the Tasmanian Devil roams the undergrowth in search of carrion. Named for their blood-curdling shriek, a Devil’s bite is about the same as a Belgian Malinois, a dog that weighs 3 times as much as this marsupial. Yet despite their tremendous jaw strength, Tasmanian Devils are more bark than bite when meeting people, as they’re quite shy when not brawling with others of their kind. 3,000 years ago, dingoes hunted the Devils to extinction on mainland Australia. But now, a transmissible cancer has replaced predation as the main threat. 

Interestingly, cancers aren’t usually transmissible. In fact, only four separate types have been observed to date in dogs, hamsters, clams, and Tasmanian Devils. They’re exceedingly rare in both animals and humans, so existing knowledge of them is fairly limited. 

Devil Facial Tumor Disease, or DFTD, works by causing solid tumor growths on the face, neck, and in the mouth with bone-snapping strength. It can displace teeth and grow through eyes and nostrils. Despite these gruesome afflictions, afflicted devils often die of starvation first. Disease progression is rapid, with death occurring as soon as three months after contracting it. To claim that DFTD is near a hundred percent fatality is generous, when most sources claim no chance of survival. 

The effect of  DFTD was immediate and devastating. By 2001, only five years after DFTD’s first sightings, affected populations saw declines of up to 80%. In 2012, some populations had seen declines of at least 95%. Now, in 2021, there’s only 25,000 devils left in the world, from the 150,000 that was estimated in 1996. Since being classified in 1996 as least concern, they were reclassified as endangered in 2008. To this day, Tasmanian Devils remain endangered. The rise of a second variant in 2014 called DFT2 has been spreading much the same, with near identical symptoms. 

It’s near unheard of for such a rare phenomenon to have a near 100% fatality rate. For comparison, mesothelioma, the cancer with the lowest survival rate in humans, has a 7.2% survival rate. But even then, chemotherapy treatments can slow progression or even cure patients completely. It’s a common treatment in both dogs and humans, and while effectiveness varies, it’s consistently proven to be a reliable treatment option. 

The catch? Chemotherapy isn’t as nearly as effective in treating DFTD. Even extremely high dosage rates given at early stages have no impact on the inevitable outcome. With no visible cure and steep population declines, extinction seemed inevitable. 

It’s In the Genes

The cause of DFTD has long since been debated. Surprisingly, the prime suspect was actually the devil itself — or more specifically, its immune system.

Tasmanian Devils have a considerable lack of diversity among the MHC gene, which plays a critical role in self and nonself recognition — or foreign materials, such as diseases or infections. A high diversity among MHC genes would mean higher resistance against pathogens, while lower would mean less. In vertebrates, all body cells have unique surface molecules that identify as ‘self,’ which allows them to pass by the immune system unnoticed and undeterred. Any other particles would be identified as non-self, and would be subsequently destroyed. 

It’s why organ transplant recipients need to take immunosuppressants for the rest of their lives, so their body doesn’t attack the donated organ. However, DFTD evolved from a cell in the devil’s own nervous system, leading to MHC antigens being shared with the tumor cells, and consequently not being perceived as a threat by the immune system. 

There’s simply been no evidence of immune cell responses in afflicted Tasmanian Devils. It’s suspected that a lack of genetic diversity is directly responsible for this, so with the Devils’ lack of MHC diversity, it’s clear why DFTD was so devastating to the population for so long.

Genes are also the reason why captive breeding programs to supplement wild populations cannot be the failsafe if DFTD continues its path unhindered. Considerable genetic diversity must be maintained, to avoid gene loss by genetic drift. If devils are evolving with DFTD, then the risk of outbreeding depression only increases as wild Tasmanian Devils would grow genetically different, and introducing captive bred, genetically distant Tasmanian Devils would create weaker generations, which would only worsen the epidemic. 

Hope for the Future 

Despite DFTD’s devastation and many, many failed attempts to find a cure for it, not all hope is lost for the Tasmanian Devil. To combat the rapid population loss consisting mostly of mature Tasmanian Devils, Tasmanian Devils have shown a 16-fold increase in the proportion of individuals that reach early sexual maturity. Before DFTD, sexual maturity occurred at around two years of age, with the percentage of one year old females breeding extremely low. Now, post-DFTD, that percentage has spiked from 12.5% up to 83.3%. 

Along with changes in sexual maturity age, Tasmanian Devils’ immune responses are also changing. Although they’re notorious for their lack of diversity among one of the most important proteins in vertebrates, a study strongly suggests that after only a few generations since the first appearance of DFTD, Tasmanian Devils are already genetically evolving for better immune response and even cancer recognition due to the strong pressure that DFTD has placed on them. In addition, 23 cases of tumor regression without human interference have been observed so far, with some even completely regressing, although the reasons why are unknown.

Yet genetic evolution isn’t the only factor contributing to the devil’s continued existence. While chemotherapy has shown little promise, immunotherapy has. Immunotherapy is the treatment of a disease by either activating or suppressing the immune system. In this case, DFTD cells were cultured in a laboratory and made to show genes recognizable as non-self by Tasmanian Devils. These cells were then injected into devils already afflicted with DFTD, where three out of five devils saw tumor regression shortly after. These promising results give hope that there could be a vaccine against DFTD in the future, but nothing is certain yet.

But Tasmanian Devils’ comeback isn’t limited to merely the island of Tasmania. In fact, just north of Sydney, Australia, eleven Tasmanian Devils have been released into a 988-acre wildlife sanctuary on September 10th, 2020. And on May 24th, 2021, the wildlife sanctuary Aussie Ark posted a video on Instagram of the confirmed births of joeys — or baby Tasmanian Devils — on Australia’s mainland for the first time in 3,000 years. These joeys contribute to the insurance population of Tasmanian Devils, or what would be the final stand against extinction.

There’s hope that their gradual reintroduction will eventually allow them to be incorporated into the wild, where their presence would help counter the major threat that feral cats and foxes present to dozens of species. Tasmanian Devils have already shown themselves capable of culling feral cat populations, which became even more urgent after the Australian bush fires that swept the continent just last year. Of course, other larger predators like the native dingo, who were responsible for the Tasmanian Devils going extinct on mainland Australia millennia ago will still pose a threat. Scientists at the UNSW have decided that the Tasmanian Devils and dingoes cannot coexist, so Tasmanian Devils will simply have to be released where they will be the apex predator of an area.

This project isn’t just a ray of hope for Tasmanian Devils alone; it’s significant to all of Australia after the devastating 2020 bushfires that killed nearly three billion animals, as well as everyone around the globe living through the COVID-19 pandemic. There may be no vaccine for DFTD yet as there is for COVID-19, but existing research on DFTD can aid in revealing how cancers evade the immune system in humans. “It’s a constant arms race of adaptation between animals and diseases,” Max Stammnitz, studying transmissible cancer genetics from the University of Cambridge said.

“It’s a constant arms race of adaptation between animals and diseases,” Max Stammnitz, studying transmissible cancer genetics from the University of Cambridge said.

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