What is causing so many raccoons to develop brain cancer?



A raccoon's brain with a cancerous tumor.




The San Francisco Chronicle today has a story which solves one mystery about raccoons but leaves open another. The first is why some raccoons were displaying baffling, un-raccoon-like behavior.

"A lot of the calls were, 'There's a raccoon sitting on my porch and he hasn't moved all day, and I open the door and he doesn't move,' and that's not normal," said (Melanie) Piazza, the director of animal care at WildCare, a wildlife refuge in San Rafael and one of several Bay Area care centers baffled in recent years by a rise in strange raccoon behavior. The centers would occasionally collect raccoons like this and try to rehabilitate them, but their condition would only worsen and the animals would eventually die. Their symptoms were unlike those of any disease the center's staff had seen before.

No one knew why the raccoons were behaving this why or why they were dying. UC Davis scientists were called in to investigate.

The mystery affliction stumped wildlife refuge centers, which are on the front lines of dealing with wild animals in the Bay Area. But after veterinary scientists at UC Davis spent two years collecting raccoons from Sonoma, Marin and Contra Costa county wildlife centers, they found an answer: Each of the diseased raccoons had a brain tumor as well as a previously unknown virus.

It is still unknown if the virus is causing the cancer, but that seems highly likely.

They also all tested positive for a specific virus in the polyoma family, called RacPyV, or raccoon polyomavirus. Other polyomaviruses affect humans and other mammals, and one particular virus is known to cause a rare kind of skin cancer in humans. That connection between the virus family and cancer tipped researchers off to testing the raccoon brains for RacPyV, said Patty Pesavento, an associate professor of veterinary pathology at UC Davis who worked on the project. ... Pesavento's next question is: Does this virus cause the tumors?

The mystery remaining is whether environmental toxins are contributing to raccoons acquiring this polyomavirus.

... Pesavento and Piazza hope also to answer eventually the bigger question: Is there an environmental cause to the disease outbreak? "Raccoons are a good sentinel species to what's going on in our back yard," Piazza said. "If they're getting cancers and living in our water sources and trash and back yards, then it's something to pay attention to."