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Cancer Could Push Some Animal Species to Extinction

The Tasmanian Devil is an icon in American animation. Many Americans first met the trickster cartoon character in 1957, when the nonchalant rabbit Bugs Bunny parachutes down to Tasmania in a carrot crate. The Tasmanian Devil, Bugs learns, is a carnivorous marsupial - found only in Tasmania - that has a pouch, pointed ears, sharp canine teeth, beady black eyes and a coat of coarse brown hair.

While the cartoon Taz still has a solid career in Hollywood, over the last decade, the population of real Tasmanian Devils has dropped from a robust 150,000 to less than half that number.

The decline, says pathologist Denise McAloose, is due to a contagious cancer that causes facial tumors.

"Tumor cells are transmitted from one animal to another through fighting or biting. They actually transmit cells that might fall out of the tumor on one animal, those get injected through the bite wound into the other [animal], and then they begin to grow."

McAloose is chief pathologist for the Wildlife Conservation Society's Global Health program. She and other conservationists fear that unless steps are taken to protect the species, it could soon face extinction.

"Some of the recommendations currently are to bring some of the unaffected animals into captivity for breeding so that we can preserve the species until treatments are discovered."

In an article published in the July edition of the journal Nature Reviews Cancer, McAloose writes that knowledge about cancer in animals is spotty, for good reason.

"We have vast savannahs that the animals live in, or we're looking through jungles, or they live underwater. So access to animals makes understanding diseases and understanding their impact in animals challenging, as does the methodologies that exist for trying to identify cancers."

The article points to other hot spots. In oceans around the world, migratory green turtles suffer from a disease that causes skin and internal organ tumors. California sea lions have a high prevalence of virus-induced genital tumors that can affect reproduction. Intestinal cancer is the second-leading cause of death among Beluga whales in North America's St. Lawrence River estuary.

"In a 17-year study, those Beluga were shown to have a much higher incidence of cancer than Beluga whales in other environments. Certain toxins and pollutants in those waters in the estuary have been associated with cancer in humans," McAloose says.

She says when toxins settle into aquatic sediments, they travel up the food chain.

"And so the mussels that the Beluga whales eat have a very high concentration of these toxins, and it's thought that ingestion of those toxins is associated with the development of the cancers that the Beluga whales develop."

McAloose says her article in Nature Reviews Cancer launches a new conversation.

"We are interested in looking at cancer from a conservation perspective, to really start to understand whether and when cancer is important in wildlife populations and the drivers of the development of cancers - for example, environmental pollution - that we might be able to mitigate against."

McAloose calls for widespread monitoring and surveillance, which she says will not only help prevent diseases in wildlife, but also advance the study of human biology and improve human health.