We don’t normally think of cancer as an infectious disease. But what if we told you there’s a contagious cancer that’s thousands of years old? This disease is not caused by a viral infection. These are cancer cells that can be physically transmitted between dogs.
In our new study at the University of Cambridge’s Transmissible Cancer Group, we found that male dogs are four to five times more likely than female dogs to be infected with the oral and nasal form of transmissible venereal tumor (DVT). Cancer cells are passed between dogs by sniffing out other dogs’ genitals.
DVT primarily affects the genital regions, causes unsightly tumors to form, and is most commonly transmitted during mating. Sometimes the cells of this disease can affect other areas, such as the nose, mouth, or skin.
Although it is a common condition affecting thousands of dogs on every continent, the oral and nasal version is rare. Oral and nasal tumors are transmitted when a dog smells another dog’s DVT-infected genitals.
In our database of nearly 2,000 DVT cases, only 32 involved the nose or mouth. In addition, 84% of the dogs with the nasal or oral form were male.
Behavioral differences between the sexes may contribute to this risk. For example, male dogs seem to have a preference for sniffing or licking female genitals, versus the opposite.
Female genital tumors, which are more exposed, can also be easier to smell and lick, unlike male genital tumors, which are often hidden in the foreskin.
an ancient cancer
The most common symptoms of facial versions of cancer include sneezing, snoring, difficulty breathing, nasal deformities, or bloody or other discharge from the nose or mouth. With treatment, the vast majority of dogs recover.
This cancer breaks the mold in a different way: DVT is extremely old. It comes from the cells of a dog that lived thousands of years ago and passed it on to another dog. Genetic testing shows it is likely a husky-like animal that lived in central or northern Asia.
Since then, living cancer cells have been hopping from dog to dog like a parasite. If we look at the tumor cells of today’s DVT under the microscope, we actually see those of the dog that lived thousands of years ago. All current forms of DVT can be traced back to the same animal.
a global parasite
DVT affects dogs around the world but is particularly associated with countries with stray populations.
Transmissible cancers are also found in Tasmanian devils and molluscs such as mussels and clams. We are not aware of any contagious tumors affecting humans.
DVT is the oldest cancer line known to scientists. It could help us gain important insights into how human tumors work. Some of the processes seen in DVT that are thousands of years old may also occur in cancers that affect our species without being detected.
Andrea Strakova, postdoctoral researcher in the Communicable Cancer Group, University of Cambridge
This article was originally published on The Conversation. Read the original.