Biology

Parasitic cancer that spreads between dogs

There is a contagious venereal dog cancer (CVTV) that has spread throughout the world through copulation. This cancer appeared about 6,000 years ago in Asia and has been spreading for centuries throughout the globe due to maritime activity.

A study published in Science has made a surprising discovery. This tumor is one of the rare types of communicable cancer.

As we have mentioned, it is transmitted through copulation , and it usually manifests as genital tumors in both males and females. It arose in an individual dog but survived by expanding beyond the death of the parent dog. In fact, it continues to spread throughout all dog populations today , and is the oldest and most prolific lineage of cancer known.

The most surprising thing about this tumor is that the cancer cells are the original dog in which it first emerged and not the dog that suffers from it . Therefore, it is a rare case that it could be said parasite cancer.

The only changes that are observed in the tumor cells of today’s dogs is that some of them have undergone spontaneous changes in their DNA and / or caused by carcinogens.

In the study carried out by the Transimissible Cancer Group of the University of Cambridge, they have compared the differences in the tumors extracted from 546 dogs around the world to see how the disease spreads and how to tackle it.

The changes in each person’s DNA tell the story of where the tumor has traveled. Using the DNA data from these dogs, they created a phylogenetic tree, with the different types of mutations in the tumors.

The origin of this rare dog cancer

Thus, they have been able to estimate that this cancer first appeared between 4000 and 8500 years ago , most likely in Asia or Europe; and that modern tumors can be traced back to a common ancestor 1,900 years ago.

Parasitic cancer
Parasitic cancer

In addition, they have also determined that 500 years ago the tumor reached America 500 years ago, when Europeans first arrived and settled. Almost all tumors found throughout America today are descended from this single introductory event.

From the Americas the disease spread to Africa and back to the Indian subcontinent, in all the places that were European colonies at that time.

The historical findings are really interesting, but the DNA has a lot of substance. Recent studies in cancer biology have made it possible to observe mutations in tumor DNA and thus identify the footprint left by some carcinogens such as ultraviolet light.

The mysterious mutagen

As a result, researchers have identified up to five carcinogenic processes that are related to human cancer such as ultraviolet light. However, one of them, called “Signature A” has a different mutational signature from other seen before: it caused the mutations in the most distant past, many thousands of years ago and no more since then.

The strange thing is that this tumor was exposed to something thousands of years ago that caused DNA damage for some time and then disappeared. It is a mystery about what could be. Perhaps something present in the environment when this cancer first appeared.

Another intriguing discovery about how tumors evolved. There are two types of selection according to evolutionary theory: positive and negative.

Positive selection is when mutations that give an organism an advantage are more likely to pass through generations. Negative selection is when mutations have a detrimental effect it is more difficult for them to pass. This selection tends to occur via sexual reproduction.

When the researchers analyzed the tumors, they found no evidence of positive or negative selection. This implies that the tumor will accumulate increasingly potentially harmful mutations over time, making it less and less suitable for its environment.

Báez-Ortega explains: «Normally, we see selection pressures that act on the evolution of an organism. These canine tumors are foreign bodies , so one would expect to see a battle between them and the dog’s immune system, leading to only the strongest tumors being transmitted successfully. This does not appear to be happening here.

“This ‘parasitic’ cancer has proven remarkably successful in surviving for thousands of years, but it is constantly deteriorating. It suggests that its days may be numbered, but it is likely that tens of thousands of years will pass before it disappears. ‘

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