The other day I went to a talk about ‘Devil Facial Tumour Disease’ (DFTD) by Hannah Siddle who is involved in the research project. It was really interesting and I learnt a lot about this project that I otherwise would not have known about and followed it up with some further research into the disease:
DFTD is found in Tasmanian Devils, from Tasmania! (!), an island off the coast of Australia. Australia once was also home to Tasmanian devils, however, it is believed they were killed off with the introduction of the dingo by immigrants.
Just so you know a bit about Tasmanian devils, they are quite like kangaroos in a way; they keep their young in pouch, delivering nutrients to them until they are old enough to come out.
Tasmanian devils are scavengers, they don’t kill their pray, and they are all very possessive over their findings. It is common to see older animals with scars from feeding times when other devils have bitten them. It is very important to note the fact they come together for feeding, and interact with each other.
DFTD looks like an abnormal growth on the face of the devils. It starts as a disease and progresses into cancer.
Once they have it, they always die due to no immune response (though due to the fact the Tasmanian devil is a wild animal we can never be completely sure). The tumour grows very quickly due to the face being made up of soft tissue so can easily grow out from the face. However on the side towards the body, it is constricted by bone. The tumour eats into the bone and this is normally the cause of the death as the animal is starved and loses body condition because the tumour uses the nutrients to grow. Other ways the animal can die is by metastatic cancers.
Because the devils have no immunity, the disease spreads rapidly. Like i said earlier, the devils often interact at feeding times and when they bite each other, often the face, the disease gets passed on. As the older of the breeds are the ones to go out and scavenge, it is the older ones which have the disease. There are much fewer devils that are under 2 years old who have the disease.
The Tasmanian devil’s immune response does not recognise the disease as being foreign.
Scientists analysed some cancer cells from different Tasmanian devils and found out they were all the same. We would expect cancer cells to be individual to the person/animal but as they were all identical it suggests it is passed on, not just developed.
All cells have major histocompatibility complex (MHC) molecules. In the immune system, the T cells look at other cells, deciding whether they are safe to be there, or, if they’re foreign in which case they need to be destroyed. Our own body cells have matching MHC molecules to our T cells, so they know they are not foreign, its only when cells come in with different MHC molecules that T cells detect a change. So, seeing as the disease is foreign, the immune system should destroy them? This suggests the DFTD cells must have matching MHC of the devils. So researchers looked into it but found the cells didn’t have any MHC molecules. They looked at a region of cancer cells and nearby cells. The cancer cells didn’t have any, but the host cells (cells supporting the tumour) did. DFTD cells might have one MHC molecule attached or none at all, so the immune system doesn’t recognise it as danger.
With this disease rapidly decreasing the population, the Tasmanian devil is now classed as endangered. Scientists are trying to find ways of switching on the MHC molecules so that the immune system can respond to them. Breeding programs such as ‘Devil Ark’ (www.devilark.com.au) try to get as much genetic diversity a possible, and the government have started the organisation ‘Save the Tasmanian Devil’ (www.tassiedevil.com.au).
- New ideas for saving Tasmanian Devils (scienceblogs.com)