An Infectious Cancer; The Tale Of A Tasmanian Devil

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Picture By Menna Jones - Wikipedia (CC BY 2.5)

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Hi everyone,

I would like to tell you a story about devils who have been suffering from an infectious form of cancer which has been killing them since the 1990s. This is the story of Tasmanian Devil, one of largest carnivores from the marsupial family inhabiting the state of Tasmania, Australia. Tasmanian Devil is a small dog-sized creature which has been threatened by a form of disease only known as the Devil Facial Tumour Disease. Due to the fact that it is an infectious form of a tumour (the only one I've ever heard of anyway), there was a lot of active searches that have been conducted to identify a completely healthy Tasmanian so that they can be isolated from the rest of the affected species. In the wild, without a facial tumour, the average lifespan for a Tasmanian Devil is 5 years (the lifespan would be relatively shorter if they were affected by a facial tumour); the lifespan for a Tasmanian Devil which is being kept in the conservation can be extended up to 7 years old.

If you look at them briefly, they seem like a combination between a small dog and a rat. They have a tail which measured around half of their average body length with a variable thickness. They were black in colour, have longer forelegs compared to their hind legs with 4 sets of razor-sharp non-retractable claws and generally, a little bit unstable due to its stocky appearances which make their centre of gravity a bit low. Despite their instability, their tails play an important role in balancing their body allowing them to move swiftly while catching prey. They were quite territorial and to mark their own area, they will emit a pungent smell which will be produced through a gland located just beneath their tail.

They were really competitive. From the moment they were born, they will have to compete with the other children for a spot among the four nipples available in a single pouch of their mother, This unfortunate phenomenon has caused the other Tasmanian offspring to die due to malnutrition and negligence when they were raised in the wild. The surviving children would be living inside the pouch for a 100 days before they will be ejected and forced to live independently. However, they were never alone as they will be guided by their mother until they would be able to be completely independent which is usually achieved when they were around 9 to 11 months old. After successfully raised a number of offsprings, the female Tasmanian Devil would be prepared for the next bout of their reproductive cycle, preparing themselves to be mated by a male Tasmanian Devil in the upcoming mating season.

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Picture Source - Max Pixel (CC0)

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Even though they were never considered monogamous, the male Tasmanian Devil would often stalk and guard their female partner to ensure they would never be wooed by another male who is horny enough to court just about anything. The male Tasmanian Devil will bring their female wherever they go and if they leave her for just a moment, she will find another male to mate with. Throughout the mating seasons, the female Tasmanian devil is known to be quite selective in terms of choosing their mating partner which is why they will usually copulate with the most dominant male which has proven themselves in a battle among males. Tough luck for those who were not succeeded! Despite the fact that the rate of pregnancy among female Tasmanian devil is relatively high, approximately 60% of the offspring born will not survive as they failed to compete with the other siblings for a nipple.

The Devil Facial Tumour Diseases

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Picture By JJ Harrison - Wikimedia (CC BY-SA 3.0)

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Even though the population of Tasmanian Devils seems restricted to Tasmania, once, they were living graciously in the mainland of Australia. There were a few theories which have been proposed to explain why their population become extinct in that particular area including the introduction of a feral dog species called the dingo. Since then, their population has been plummeting and a couple of decades ago, in 1996, one of the most vicious forms of cancers has been identified, killing the remaining species of Tasmanian Devil, threatening them towards extinction. The disease was called the Devil Facial Tumour Disease (DFTD). The most interesting part about this disease was there were two different kinds of cancers which can affect the same creature at one time. Each cancer was found on a different gender of the Tasmanian Devil but both of them have an equal capability to affect each other, often found on the same individual of a Tasmanian Devil.

It's pretty much odd to hear about the occurrences of an infectious type of a tumour since generally, a tumour is not infectious (except if it is being caused by microbial agents i.e. Epstein Barr virus). The Devil Facial Tumour Disease is a form of a tumour which affects the face of the devil, creating multiple growths which kind of made their face look disfigured. After having experienced an extinction event in the mainland Australia, this particular creature is currently on the verge of extinction by this form of cancer which has been killing approximately 90% of the total population of Tasmanian Devils inhabiting Tasmania. In April 2018, a paper written by Elizabeth P. Murchison et al which was published in the Journal of Cell has identified a potential form of treatment to treat debilitating cancer that has been spreading like a wildfire among the population of Tasmanian Devils; the treatment was chemotherapies.

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Picture By Mathias Appel (CC0)

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Unlike any kind of infections, this facial tumour can't be treated by simply giving the Tasmanian Devil some antibiotics. Eventually, the immune system of an individual Tasmanian Devil would recognise the cancerous cell which inhabited the circulation of the creature as their own cell. It's kinda tricky, usually, if a foreign invader gain access into our circulation, our immune system would quickly recognise those cells as foreign due to the fact that they were having a different set of recognition component presented on the surface of the cell called the major histocompatibility complex (MHC). In cancer (both benign and malignant), there is an uncontrollable cellular division which usually caused by certain factors which can include infection, genetics, diet or any relevant environmental components such as exposure to radiation etc. The thing that differentiates between a benign and a malignant tumour is its capability to spread and invade the other organs which are usually harmful to its respective host.

The tumour/cancerous lesion which has been discovered on a Tasmanian Devil is infectious. It might be a little bit confusing and weird to consider the possible mode of transmission of a tumour among the population. I mean if the infecting tumour cell of another Tasmanian Devil trying to invade the others, the tumour should be recognised as a foreign cell thus as a result would be eliminated by the host immune system. The only possible way of how this particular creature can be affected by the tumour of another is if the capacity of their own MHC-identifier has gone haywire i.e. in an immunocompromised Tasmanian Devil but we can't really say that 90% of the population of this particular creature which has been killed by this form of disease was immunocompromised, can we? There were a few factors which kinda predisposed this particular creature of getting this form of a facial tumour:

• Lack of Genetic Diversity: As the population of Tasmanian Devils is restricted to the island of Tasmania, they have been living closely among themselves which resulted in interbreeding that would end up creating a minimally-diverse population. How can they not? I mean, if there is a disease which has been obliterating the capacity of their own population, the female Tasmanian Devil can't really be picky about the male they want to copulate with (possibly among siblings too). This would result in an almost similar appearance/structures of MHC making it difficult for the immune system to differentiate between a self and a non-self cell.

• Competitive Biting: Just like what I have said before, Tasmanian Devils especially the male type are very much competitive. During the mating season, when male Tasmanian Devils were busy establishing their dominance, they will often bite the face of another male Tasmanian Devil which usually end up in a considerable amount of blood loss and sometimes a little bit of meat with it. This act like an accidental form of an invitation for the cancerous cells to enter the circulation of a healthy Tasmanian Devil. It's unfortunate for the nature to make them so aggressive even to someone as disfigured as an affected Tasmanian Devil.

• Absence of MHC Molecule: In some Tasmanian Devils, the overgrowth tissue which can potentially be bitten during a fight lack the MHC molecules in its surface. This often results from genetic mutations which confer a better camouflaging effect to a cancerous tumour when invading a healthy Tasmanian Devil. This feature is common among the first variant of a tumour which appears in 1996. It is relatively unknown if a second tumour adopted the same mechanism to better infect a new host as much research is needed to analyse and understand its pathologies.

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Picture By Charlieatyourservice - Wikimedia (CC BY-SA 4.0)

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It is important to understand that, the problem which seems to cause cancer lies within the capability of a cell to divide. Cell division is usually triggered by a specific signal which allows an organism to develop normally. However, if the signal to divide were continuously emitted to the growing cell, the cell division wouldn't stop which resulted in an abnormal growth of mass hence the treatment should focus on interrupting this chemical signal. Most of the drugs which are designed to treat cancer in the Tasmanian Devil population will interfere with the binding of chemical signal to a specific receptor that will usually allow protein synthesis, thus growth.

Even though most of the results yielded are highly experimental, it was established that the cell of a Tasmanian Devil resembles the cell of a human in a way that we can use the same chemotherapy agent to kill off a cancerous tumour. It is worth noting that most of the experiment conducted to find a cure for the Devil Facial Tumour Disease were carried out with cells in the Petri dishes, not to the creature itself. Whether or not the drug which has been used would be suitable for the creature's survival were relatively unknown. I would say that much experiments need to be conducted to ensure the viability of this mode of treatment to treat the Devil Facial Tumour Disease.

References and further reading materials

• Tasmanian Devil, Britannica. Retrieved on June 13th, 2018.
• Tasmanian Devil, Wikipedia. Retrieved on June 13th, 2018.
• Tasmanian Devil, Sarcophilus harrisii. Retrieved on June 13th, 2018.
• Contagious cancer is killing off Tasmanian devils, but there might finally be hope. Retrieved on June 13th, 2018.
• The Origins and Vulnerabilities of Two Transmissible Cancers in Tasmanian Devils. Retrieved on June 13th, 2018.

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