Cancer found to spread among world's dogs as a parasite:

TheStar.com - Cancer found to spread among world's dogs as a parasite: "A strange form of cancer is being transmitted as an infectious agent among the world's dogs, without help from viruses or bacteria, a research team in England has found.
The discovery, reported in the journal Cell, shows how a single cancer cell can become a parasite, grow and then spread worldwide in susceptible animals. The researchers said the disease is apparently transmitted sexually. It arose in wolves as much as 2,500 years ago, then spread to coyotes and dogs.
The new study is the first to document cancer being spread from animal to animal on its own. Viruses are known to cause some cancers when they damage critical genes during infection. But now it's clear cancer can get around solo, then spread through a population."