Tasmanian Devil Facial Tumor Disease

by tahliajohnson (student)

University Degree Biological Sciences

Tahlia Johnson Student ID: 220083677

Tasmanian Devil Facial Tumour Disease

Tahlia Johnson

220083677

Word count: 1,528

Turnitin score: 3%

7 pages in total

Introduction

The Tasmanian devil (Sarcophilius harrisii) is the largest existing carnivorous marsupial and is currently threatened by a transmittable cancer known as “Tasmanian Devil Facial Tumour Disease” (DFTD). The first suspicion of DFTD came in the late 1990’s through a tourist’s photograph while travelling in the bush of Mt. William National Park, Tasmania. In the past 15 years, almost 90% of Australia’s Tasmanian devils have died due to the new arising cancer. The cancer is spreading so rapidly that scientists estimate that within 5 to 15 years, the disease will have spread to the entire species, causing extinction.

The aggressive tumour causes death within 6 months because of airway obstruction and incapacity to consume food. DFTD is transmitted from biting during courtship battles and fighting in which “facial tumour cells of one devil are transferred to another as an allograft” (McCallum, 2007). Scientists are still trying to discover a vaccination, but unfortunately they are many years away from completely understanding the disease.

History of the disease outbreak

In early 1996, a photograph was taken of a Tasmanian devil by Chris Baars, with an unusual facial deformity (Hawkins & McCallum, 2008, p.631). It was described as a tumour, but preliminary investigation was put off due to scientists not having knowledge of DFTD. A year later the first case was confirmed when a devil had been collected and examined in the same area where the photo had been taken in north-east Tasmania, 1997.

The disease outbreak was discovered in north east Tasmania, and having information from the most recent investigations (Hawkins & McCallum, 2008), that indicates the disease to have spread to devil population in the north and north east, to the east coast and the midlands, as far west as Bronte park (see fig 1) . There is no evidence to believe the disease has spread to the west coast of Tasmania as of yet. In 2009, studies undertaken by the Tasmanian Department of Primary Industries, Parks, Water and Environment showed that DFTD could be found at 64 locations across more than 60% of the state.

Figure 1. The area and year of DFTD emergence. Retrieved from McCallum, H. & Tompkins, D.M. (2007) Distribution and Impacts of Tasmanian Devil Facial Tumour Disease. EcoHealth Journal Consortium.

Symptoms of the disease

Devil facial tumour disease has a six month incubation period and is a rapid killer. Once the animal has contracted the cancer, it then destroys the inside of its mouth, filling it with small lesions and lumps. These then grow to become large tumours making it extremely hard to eat. The tumours are also found to appear around the devils mouth, face and neck. As Hawkins ...

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Figure 1. The area and year of DFTD emergence. Retrieved from McCallum, H. & Tompkins, D.M. (2007) Distribution and Impacts of Tasmanian Devil Facial Tumour Disease. EcoHealth Journal Consortium.

Symptoms of the disease

After a few months of having been infected, the animal’s body starts to weaken which makes it difficult to fight for food against the stronger devils. After going without food the animal slowly starves and the body begins to breakdown. McCallum and Hawkins, 2008, state that the infected devils appear to die within three to six months of the physical symptoms appearing.

The tumour is transmitted by cancerous cells being transferred from the mouth of one devil to the head of the other during mateship battles, fights for food and intercourse. Studies of the disease show that it can be transmitted to any Tasmanian devil, but occurs mainly in adults.

Effects on the Tasmanian devil population

There is still no cure as of yet for DFTD, but there is a test to diagnose the devils with the disease. Scientists from the University of Tasmania report they have developed a preliminary diagnostic test that reveals which devils carry the cancer in their blood before the physical symptoms show (Owen & Pemberton, 2005). Scientists are still researching the disease to establish what types of cancer cells are involved.

The disease has killed roughly 90% of Australia’s Tasmania devils, and scientists estimate that within 5 to 15 years, the fatal disease will contaminate the remaining devils, causing extinction to the species.

The DFTD has had a dramatic impact on the Tasmanian devil. In the areas that have been surveyed since 1997, the disease has made its greatest impact on the devil in the areas where the highest densities of adults are found. In low density areas such as south-west Tasmania, the impact on the populations has been less severe. Studies show that out of all the captured devils, those that had contracted the disease where found to be typically older than those that were healthy; suggesting that the disease primarily affects the older individuals.

Across Tasmania, there had been an average of a 70% decline in devil sightings since DFTD emerged, and in the north-east region where the disease was initially discovered, the sightings have had a 95% decline. Table 1 (Hawkins C.E, & McCallum, H., 2008) shows the average population decline since the outbreak in 1996, when there were roughly 150,000 devils in the wild.

Table 1: Average Population decline between 2004 & 2008 (Hawkins C.E, & McCallum, H., 2008). Information Retrieved from: .

As this decrease rate of devil sightings is extremely alarming, the Tasmanian devil became listed as ‘endangered’ under the Australian government national environmental law in May 2009.

Prior to the outbreak of DFTD, the Tasmanian devils were spread out right through the mainland of Tasmania, except for parts of the south west of the island. Studies show that the distribution of the devils hasn’t changed since the emergence of the disease, only the density has (McCallum & Tompkins, 2007).

Allograft theory of disease transmission

Initially, the way the devils were contracting the disease was unknown, until the idea of it being transmitted by allograft came about in 2006 (Pearce & Swift, 2006). The allograft theory is the name given to the idea that cancerous cells from one Tasmanian devil are transmitted and infect another devil just by biting.

The chromosomes in the tumours of every individual infected undergo an identical complex rearrangement. Because of the fighting behaviour in the Tasmanian devil, it is proposed that “the cancer is transmitted by allograft, whereby an infectious cell line is passed directly between the animals through bites they inflict on each other” (Pearce & Swift, 2006). Further studies recognised that the tumours only contained 13 chromosomes, where the Tasmanian devil has 14.

The majority of devils found with the disease have been adults, therefore making the mature devils the carriers of DFTD. The infection is spread by biting, and once it inhibits and animal, the cancer starts off small then spreads rapidly within a few months to the whole body, shutting down the main bodily functions.

Interactions between the animals include mateship battles, intercourse and fighting for food, which are all daily routines, making it extremely easy for the disease to rapidly spread.

Strategies for saving the species from extinction

Once the outbreak occurred in 1997, scientist and conservationists began to find a cure for the cancer, but since the population numbers dramatically declined over a 10 year period, they had to start making strategies towards conserving these animals as well.

Since then there are numerous conservation groups and wildlife parks that have created strategies for saving the species from extinction including groups such as Save the Tasmanian Devil Program, Devil Island Project, Devil Ark, UTAS Save the Tasmanian Devil Appeal, Tasmanian Devil Conservation Park, Fighting Extinction Zoos Victoria and many other conservation groups.

Population management options include isolation, which involves isolating the uninfected devils from the infected and moving them to a new habitat, an example of this is the strategy being put in place by the Australian Reptile Park. The program called ‘Devil Ark’ Insurance Population aims to breed up to 500 devils on mainland Australia. While this idea is plausible, mating in captivity limits genetic diversity, evolutionary change and natural selection. Another option is culling the devils that have been diagnosed with the disease; this will help reduce the transmission rate. Since there is no evidence of this affecting the population level, this plan will probably stay in place until the disease is fully understood and a cure has been found.

It is important for the Tasmanian devil not to become extinct because it not only an important part of the Tasmanian ecosystem and is a unique species, but because the devils contribute a large amount to the landscape and environment.

There is already a sign of change in the landscape from the decrease in devil numbers, which impacts not only the ecosystem but our agricultural industries. Tasmanian devils are also a main predator, without these predators, the introductions of invasion species such as feral cats and dogs have an opportunity to expand.

Conclusion

In the 15 years that the disease has been evident, the population of the Tasmanian devil has tragically declined causing devastation to the species. Unfortunately, the cancerous cells of the infected devils are transmitted by an allograft in their everyday routines such as fighting, mating and food interactions. This means that the time left until extinction is in the near future. The strategies being put in place can have great outcomes, but without a cure, nothing is certain to stop the spread of this lethal disease. The future and life dependency of one of Australia’s native species now lies with scientists; we can only hope that finding a cure is closer then the extinction of the Tasmanian devils.

References

Platt, J. R. (2009). New test create hope for cancer plagued Tasmanian devils. Retrieved from: http://blogs.scientificamerican.com/extinction-countdown/2009/04/03/new-test-creates-hope-for-cancer-plagued-tasmanian-devils/

McCallum, H., Tompkins, D.M., Jones, M., Lachish, S., Marvanek, S., Lazneby, B., Hocking, G., Wiersma, J. & Hawkins, C.E (2007). Distribution and Impacts of Tasmanian Devil Facial Tumour Disease. EcoHealth Journal Consortium, EcoHealth 4, 318-325. doi: 10.1007/s10393-007-0118-0

Atwill, P. & Wilson, B. (2006). Ecology, An Australian Perspective. Melbourne, Australia: Oxford University Press.

Hawkins, C.E., McCallum, H., Mooney, N., Jones, M. & Holdsworth, M. (2008). The IUCN Red List of Threatened Species, Sarcophilus harrisii. Retrieved from:

Owen, D., Pemberton, D. (2005). Tasmanian Devil: A Unique and Threatened Animal. Melbourne, Australia: Griffin Press.

Pearce, A.M., & Swift, K. (2006). Allograft Theory: Transmission of Devil Facial Tumour Disease. Nature 439. Retrieved from:

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