First recorded in northeastern Tasmania in 1996, devil facial tumour disease produces large tumours around the mouth and face that interfere with feeding. Genetic analysis showed that tumours from widely separated animals were nearly identical to each other and different from their hosts, meaning the tumour is a single clonal cell line that originated in one devil and has been transplanted between individuals ever since. A second, independently arisen transmissible line, DFT2, was identified in southern Tasmania in 2014.
Transmission happens during the biting that accompanies feeding and mating. Low genetic diversity in the devil population, particularly across immune-recognition genes, appears to have made it harder for a recipient's immune system to identify the foreign cells as foreign.
The disease has driven population declines exceeding three quarters in affected areas, and the species is listed as Endangered. It has not, however, gone extinct. Some populations now show signs of resistance, and genomic work has detected rapid changes in immune-related regions of the devil genome, though the eventual outcome is unresolved.