Cancer as Contagion: The Tasmanian Devil Facial Tumor Disease
Written by Elisa Dong '24
Edited by Megan List '24
Credit: Wikimedia Commons (1)
The world’s largest carnivorous marsupial: the size of a small dog, endemic to the Australian island of Tasmania, and winner of the title “Strongest bites per unit body mass of any predatory land mammal.”
Tasmanian devils face an unusual and devastating epidemic: a transmissible cancer known as devil facial tumor disease (DFTD), with a near 100% fatality rate. Once the cancer spreads to a host devil, it escapes immune recognition, becomes malignant, and develops a disfiguring mass on the face that interferes with the devil’s feeding habits. Death often results within 9-12 months—quick, and lethal . Since the disease first emerged in 1996, devil populations have plummeted by 80%, evoking catastrophic prospects for the survival of the species .
The origins of DFTD in tumor cells is markedly unique. As of 2022, only three transmissible cancers have been identified among mammals: dogs, Syrian hamsters, and Tasmanian devils. Six more transmissible cancers are known among bivalves (e.g. mussels and soft shelled clams) . With a scant total of nine transmissible cancers detected among the millions of studied species on our planet, the transition from genetic disease to contagious organism constitutes an incredibly rare event.
How does a tumor become transmissible in the first place? Malignant cancer, a genetic disease of uncontrolled cellular replication, is characterized by the spread of mutated cells through nearby cells, tissues, and body parts. These transmissible tumors succeed in colonizing a new host by escaping their immune system and adopting their resources, just like any other infectious disease. All cases of DFTD originate from a single, mutated cancer cell, evidence that the disease does not induce cancer, but rather is the cancer itself, as opposed to diseases like HPV . Contrary to the traditional paradigm of cancer as a genetic disease, this contagious cancer spreads from host to host and uses the mutations that occurred in the cells of the original devil to disrupt the functions of a new, unsuspecting host.
Tasmanian devils are particularly vulnerable to this development due to their low genetic diversity and population size, established by an evolutionary bottleneck that occurred in their migration from the Australian mainland [3, 4]. This can vastly increase the risk of deleterious mutations accumulating within the population and leave them with a lower capability to adapt and evolve.
By the 1990s, researchers began to notice Tasmanian devils succumbing to a facial tumor that spread through their mating activities of biting and fighting. Notably, this left the devils who were most reproductively fit—the ones engaging most aggressively in mating behaviors—with an increased susceptibility . In 2003, the Tasmanian government put out $1.8 million in funding to increase conservation efforts, but the population continued to decline, up to 50% in just 2007 .
These facial tumors had profound ecological effects on the species. Devils, known to go through multiple rounds of mating, would now only reproduce once due to drastically shortened lifespans, and reproduction would begin earlier due to reduced competition . The population’s very life history was altered in just a couple of generations.
Credit: Getty Images
Biting remains a part of the Tasmanian devil’s mating ritual, largely responsible for the spread of the facial tumor.
For a disease that quickly threatened to push Tasmanian devils to the brink of extinction, researchers and conservationists rushed to find solutions. Populations were translocated to islands or isolated behind barriers, and monitored for signs of disease. Vaccines were also put into trial—evidence from a 2021 experiment showed that a prophylactic vaccine could potentially prime the immune system before infection, but complete tumor regression in Tasmanian devils remains elusive .
Thankfully, in 2022, long-term field studies and simulation modeling suggest that devil-DFTD coexistence is a more likely scenario than extinction. Research from one study published in 2020 used phylodynamics to quantify the precipitous decline of DFTD’s recent transmission, suggesting that it had transformed from emergent to endemic within the devil population . Once unfathomable, the disease’s assault on the devils is showing signs of waning.
The struggle against DFTD is far from over, requiring a combined, interdisciplinary effort of detection, breeding programs, vaccine development, and more. But while devils are not quite in the clear—yet—recent developments, aided by human involvement and conservation efforts, makes a future of saving these critters a genuine possibility.
Credit: Aussie Ark
End note: The author chooses not to include photos of the Tasmanian devil facial tumor due to the graphic nature of their injuries. Please note this warning if you choose to search for them!
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(1) Wikimedia Commons
(2) Getty Images