Last week, the International Union for Conservation of Nature (IUCN) released its latest report on the state of the world's species. It makes for gloomy reading. Although there have been a few triumphs — species increasing their numbers thanks to conservation efforts — the general picture is one of decline. A quarter of all mammal species are now endangered, mostly because their habitat is disappearing. But of all the mammals now on the endangered list, from the fishing cat to the Caspian seal, the most startling is the Tasmanian devil.

Tasmanian devil

Tasmanian devils live on the island of (surprise!) Tasmania, off the south coast of Australia. They are marsupials: their young are born tiny (about a third of a gram — that's a hundredth of an ounce), then fed on milk and carried in a pouch. As adults, devils are thick-set, thuggish-looking animals, with massive teeth that they use to chomp up carcasses, bones and all. Although they are far from enormous — the biggest males weigh in at around 14 kilograms (30 pounds), about the size of a French bulldog — Tasmanian devils are the largest carnivorous marsupials to have, so far, escaped extinction.

But over the last 12 years, the population has crashed — in some areas, population numbers have fallen by 90 percent. The dramatic decline has led the IUCN to move the species from "least concern" a decade ago to "endangered" now. Some think it could be extinct within 25 years. The reason? An infectious cancer.

Some human cancers are infectious in the sense that they are caused by infectious viruses. Cervical cancer, for instance, is caused by human papilloma virus, which spreads from one person to another during sex.

But the cancer that's killing the Tasmanian devils is different. The cancer cells themselves are infectious.