Signs shown of genetic resistance to DFTD

Research by an international team of scientists, published at the end of August in the journal Nature Communications, shows two regions in the genomes of Tasmanian devils (Sarcophilus harrisii) appear to be evolving in response to the fatal facial tumour disease that has ravaged populations in the wild for almost 20 years.

Evolutionary geneticist Andrew Storfer from Washington State University, and geneticist Paul Hohenlohe from the University of Idaho, compared tissue samples collected from Tasmanian devils by Menna Jones over a 17-year period. An Associate Professor and wildlife ecologist at the University of Tasmania, Jones is credited with first identifying DFTD during the mid-1990s, and she subsequently established long-term field sites to study the animals. In less than 20 years populations of devils in the wild have declined by more than 80 per cent.

Jones, who is a co-author of the paper, said two small genomic regions were identified in the recently collected DNA samples from three sites: Narawntapu in Tasmania’s north-east, West Pencil Pine in western Tasmania’s Cradle Valley, and Freycinet, on the east coast. They all exhibited significant changes in response to the strong selection imposed by the disease. Continue reading Signs shown of genetic resistance to DFTD

Transmissible cancers in dogs and Tasmanian devils

Figure 1.

The Tasmanian devil, the world’s largest marsupial carnivore, is facing possible extinction in the wild due to a transmissible facial cancer known as Tasmanian devil facial tumour disease (DFTD) (Figure 1). DFTD is spread when living cancer cells are spread between animals by biting. In DFTD, the living cancer cell itself is the infectious agent of disease and it remains unclear why these cancer cells are not detected and rejected by the devil’s immune system. The distressing plight of the Tasmanian devil has drawn attention to the existence of transmissible cancers, parasitic cancers spread by the transfer of living cancer cells between hosts. However, it remains a surprisingly little-known fact that the only other transmissible cancer that bears any resemblance to DFTD is a dog cancer that is right under our noses here in Australia.

Canine transmissible venereal tumour (CTVT) is one of the world’s most remarkable cancers. It is a transmissible cancer that affects dogs worldwide. Usually spread during coitus, the disease is most prevalent in areas with large numbers of free-roaming sexually active dogs. The tumour affects both male and female animals, and appears to affect dogs of any breed. CTVT generally manifests itself in the appearance of tumours in and around the genital area, often at the base of the penis in males and in the vulva of females. Starting as small shiny pink/grey lesions, the tumours can progress to become very large and multi-lobulated (Figure 2). The tumour may aggressively invade surrounding tissues and become ulcerated and secondarily infected. However, a combination of surgical debulking and chemotherapy (using vincristine) is often curative.

Figure 2

Genetic studies have provided strong evidence that CTVT is in fact one living cancer cell line that has spread worldwide with dogs. Thus all CTVT tumours are derived from a single original tumour that arose once and has been transmitted through the dog population as a clone. The tumour itself bears closest genetic resemblance to wolves, suggesting that this tumour may have first arisen in a wolf before hitch-hiking its way into dogs through sexual contact. Genetic evidence suggests that the tumour may in fact be quite old, and that the original wolf that gave rise to the tumour may have even lived thousands of years ago. CTVT is by far the oldest known continuously growing cancer in the world. Continue reading Transmissible cancers in dogs and Tasmanian devils