Tasmanian Devils Catch Cancer

Photo Credit: PanBK/Creative Commons
The Tasmanian devil is a marsupial carnivore, best known to most Westerners through the Warner Brothers cartoons. It has acquired a vicious reputation because of its array of screams and shouts, its voracity (it is capable of gulping down 40% of its own weight in half an hour, and often does so as part of a group activity, in a sort of miniature shark feeding frenzy), its indiscriminate diet (small mammals, perhaps including animals as large as sheep; birds, reptiles, insects; carrion; other Tasmanian devils), and its powerful bite (nine times as powerful as a dog's, and capable of shearing through the bones of cattle; it routinely eats every scrap of an animal, not just the meaty part favored by bipedal predators). Until recently, however, the most compelling reason to fear the devil was its odor, said by some to be the most offensive smell produced by any animal. Supposedly it's more nauseous than the scent of the skunk, and a powerful deterrent.
What's happened recently: A contagious cancer has devastated devil populations. The cancer causes tumors on the face and in the mouth. The species, already in trouble, is now on the brink of extinction. More from Scientific American:

Unlike human and most other known mammalian cancers, Devil Facial Tumor Disease (DFTD) spreads from one individual to another individual through physical contact—from a bite or even a casual touch. 'Just imagine a human cancer that spread through a handshake,' said study co-author Stephan Schuster.

(The full article tells what scientists are doing about the problem: Observations: Sequencing of Tasmanian Devil Genome Suggests New Attack on Contagious Cancer, Clues for Conservation)

The particular habits of devils—like biting each other during sexual intercourse—helps spread the disease.
This cancer is unlikely to ever affect humans. On the other hand—and this is the scary part—there's nothing to keep us from evolving our own contagious cancers.

And the flames of the tripods expired. And Darkness and Decay and the Red Death held illimitable dominion over all.
--"The Mask of the Red Death"
   Edgar Allan Poe