The source of a cancer that affects dogs around the world has been traced by scientists and vets at UCL (University College London) to a single wolf or dog, which probably lived in China or Siberia more than 250 years ago. In canine transmissible venereal tumour (CTVT), the cells of the tumour itself are transmitted between dogs during sex. No equivalent form of contagious cancer exists in humans, but the new findings challenge current thinking about the nature of cancer.
Some human cancers such as cervical cancer may be considered to be 'catchable', as they are initiated by viruses transmitted between people in the case of cervical cancer, by certain types of papilloma virus. What is unusual about CTVT in dogs, however, is that no virus is involved the cancer itself is effectively passed on.
In a paper published in the journal Cell, veterinarian researcher Dr Claudio Murgia conducted forensic DNA tests on tumour tissues from 16 dogs affected by CTVT. The dogs were being treated for the cancer by vets in Italy, India and Kenya who provided the biopsies. He found that in all cases, the tumours were genetically different from the affected dog in other words, the cancer had come from a different dog. A further analysis of 40 tumours archived in vet labs in five continents showed that the tumours were genetically almost identical and demonstrated that CTVT originally came from a single source and has since spread across the globe.
To trace this source, the UCL team worked with geneticists and computer experts in Chicago and compared the DNA in the tumours to that in specific dog breeds. They found that the cancer most likely first arose in either a wolf or an 'old' Asian dog breed such as a Husky or Shih Tzu. The number of mutations accumulated in the DNA also enabled the researchers to obtain a rough estimate the age of the disease, which came out at around 1,000 years and not less than 250 years old.