devil facial tumour disease - dftd

Devil facial tumor disease (DFTD) is a debilitating cancerous sarcoma that affects 30-50% of wild Tasmanian devils. The disease is characterised by the development of ulcerated tumors around the jaws and head of the animal. The disease is fatal and an individual usually starves to death in 3-5 months.

The disease is believed to have started from a chance mutation in the far north east region of the state in Mount William National Park. The first case of DFTD was witnessed by Christo Baars, a wildlife photographer working in the area in 1996. Some anecdotal evidence suggests that the disease may have been in the population as early as 1984 but no photographs or samples exist from that area.

Mid 1990s - Reports of devils becoming rare in far north east.
1996 - Infected devil photographed by Christo Baars at Mt William
1 month later NCB found very few devils in this past 'devil heaven'
DPIWE Pathologists suggest cancer caused by an infectious virus.
1997 to 1999 - Occasional reports of DFTD from central east coast.
2000 - 1st specimens for pathology from Bicheno by Dr. Menna Jones (UTAS)
2001 - Reports of devils becoming scarce in the east and midlands.
2002 - NCB spot-survey finding DFTD active in midlands. Increasing reports by landowners of disease and scarcity of devils.
2001/2003 - Info on population effects of DFTD from Menna Jones.
Early 2003 - 1st press- huge national and international interest.
DPIWE Animal Health pathologist Dr. Brad Chadwick and Dr. Richmond Loh commit to in depth DFTD research.
DPIWE minister 'launches' DFTD Pamphlet asking for public records.
Mid 2003 - NCB statewide survey accelerates with the help of Dr. Marco Restani (USA). DFTD widesprend in east and central Tasmania including first WHA record.

The spread of DFTD is unusual as each tumor that has been investigated is a clone. That means that it has the identical misreading of the original host’s genetic code, with the same number of damaged chromosomes. The fact that each tumor is identical suggests that the disease is not environmentally stimulated by chemicals or carcinogens but is directly transmissible between two individuals.

For this situation to have developed the tumors are believed to 'allo-graft' or transplant between two individuals.
The successful allo-graft relies heavily on the lack of genetic diversity in the devil population. The very low heterozygosity in devil populations may be the result of 'genetic bottlenecking'. Several times in European history the devil population has crashed to very low numbers. Anecdotal evidence suggests three of these crashes have been caused by disease. Devils were also maintained at very low numbers for an extended period of time by bounty systems and unwarranted persecution from landholders who believe that devils threaten their stock. The population that recovers from a smaller founder group or small genetic base becomes more and more inbred over time. Every substantial drop in numbers exaggerates the process for the growth of the tumor and its reduced ability. The individual devil usually dies of the disease through starvation or failure of body functions within 3 to 5 months.
Because of the way devils infect each other with DFTD there is also opportunity for exponential spread of the disease through a population.

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Currently DFTD has not spread through the populations of devils in the west of the state. It is believed to affect 64% of the state. Of this 64% that it affects the current estimate is that 50% of devils have died in the last 10 years. One problem is that DFTD affects the older more experienced devils because they are more combative. The populations are therefore not just getting smaller but they are getting younger and less experienced. DFTD is also affecting younger devils as the number of experienced adults reduces in an area. The second main problem is that devils are not currently developing any immunity to DFTD so in areas such as Mount William National Park there is still an infection rate of approximately 30% after 10 years.

One significant finding is lack of DFTD in the western 36% of the state and Narawntapu National Park on the central north coast. It is believed that these areas are isolated from the spread of disease. Boundaries of habitat change between the eastern and western population and inhibit gene flow east to west.

This is further supported by some recent evidence that the western group may even be a separate gene pool. Therefore with natural boundaries separating the population into two genetic groups it is hopeful that DFTD will not spread into these areas. Several scientists believe that it is only a matter of time and the boundaries are only slowing the spread of DFTD not stopping it. The longer DFTD is in the population without any immunity developing the greater the chance of these natural boundaries breaking down.

The western population may also be free of DFTD due to its very low natural density. It seems through some evidence that the lower the density of devils in a region the less affect DFTD has on that population. One example of this is Cradle Mountain. DFTD was first observed in the area around 18 months ago. Since then only three individuals have been observed with the condition. It is thought currently that the population has dropped by less than 20%. In contrast some areas of the North East and the central Plateau are believed to have suffered 50 to 80% declines in a similar period.

Currently there is no treatment or vaccination for DFTD. Because of the complex nature of the problem, being both a cancer and a cancer spread through personal contact it will be very difficult to control. With knowledge of the disease, advanced cases of DFTD are easy to distinguish; minor or developing cases are much harder. Devils can carry all manner of injuries and other diseases, sometimes even sarcomas believed to be from the constant traumatisation of old injuries.

In order to understand DFTD we have to be able to identify the disease.

Early manifestations of the disease can be difficult to identify and can resemble scaration. Biopsies are taken to confirm the presence of DFTD through the known rounded and simple structure of the cells and the 'genetic blueprint' of the tumours.

We can identify DFTD from them but still do not have a pre-clinical test (eg a blood test) which gives us difficulties with survey and study of wild devils and assessment and management of captive devils.

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Other Threats

Numerous threats have plagued devils throughout the 200 years since colonisation. These include;

  • Habitat destruction and fragmentation through urbanisation, forestry and primary industry
  • Fragmentation of genetic groups
  • Bait poison, fertilizer and chemical usage within forestry and primary industry
  • Competition with feral and domestic pests including the recent release of the fox (Vulpes vulpes) into Tasmania
  • Predation from feral and domestic dogs and cats
  • Persecution from graziers and landholders
  • Roads and traffic
  • Licensed culling of prey species
  • Fear and ignorance within the general public and a lack of scientific knowledge and long term monitoring of devil numbers.

Most of these threats are increasing in the impact that they are having on the population. There are unfortunately threats of human encroachment into their once Gondwanan habitat and therefore threats that we have the greatest control of.

It is unlikely alone that DFTD will result in the extinction of Tasmanian devils but combined with the numerous threats already impacting on devils their long term future is certainly not secure. Accordingly devils are now listed as a vulnerable species under the threatened species act. Ten years ago they were considered common, abundant and secure!

Find out more about DFTD and Tasmanian devils on the Department of Primary Industry and Water's website

www.tassiedevil.com.au

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Photo - DPIW
 
 
 
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Devils@Cradle - Tasmanian Devil Sanctuary