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Our precious mutts can carry one of the strangest diseases known to date: a form of badually transmitted cancer that has been transmitted from host to host for thousands of years. Now, a large group of researchers explained having retraced the history of the evolution of this disease, from the first dogs until its appearance. And it's even stranger than expected.
Most cancers – the mutant, uncontrollable and harmful growth of a body's cells – are unique. Of course, if you and another person have a specific type of bad cancer, these cells will behave the same way. But your cancer cells belong to you alone and they will be significantly different from the cancer cells of another person. You can not actually infect your cancer, especially because our immune system can usually recognize and destroy foreign human cells.
That said, there have been rare examples of cancer transmission in humans. These have largely occurred in people whose immune systems are weakened and who have undergone organ transplants from a donor with cancer or from a mother to a transplant. Other in the womb. But these are isolated cases of short duration, cancer never spreading again.
However, some cancers in some animals have been able to lead an infectious life by themselves, having "learned" to escape from their original hosts and to spread freely among the population, as in the case of animals. a bacterium or a virus. One of these immoral agents is known as canine communicable venereal tumor, or CTVT. And as the name suggests, it is badually transmitted.
Our results show that for at least 1,000 to 2,000 years, CTV has evolved differently from human cancers.
The study was not intended to determine exactly where and when CTVT would have emerged, said Gizmodo, lead author, Adrian Baez-Ortega, a bioengineering engineer and PhD student at the University of Cambridge in the UK, in a post electronic. The team, however, found evidence that it was first created among dogs in Asia between 4,000 and 8,500 years old. This is broadly consistent with the results of a study conducted last year that found CTVT to be the last genetic legacy of the first dogs that migrated from Asia to the Americas during this period.
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Baez-Ortega and his team were more interested in tracking the genetic pathway that took the CTVT since he was released from his confinement, especially when he started to spread quickly in the world over the last thousand years. And there, they found really special differences between this cancer and other cancers.
"Our results show that for at least 1,000 to 2,000 years, VCT has evolved differently from human cancers," he said. "While human cancers evolve through the continuous acquisition of mutations that confer a benefit to some of the cancer cells, which makes them more fit for their environment (called" positive selection "), CTVT does not no sign in this sense. We conclude that CTVT has really stopped evolving in a particular "direction" and that its evolution is therefore largely undirected or, if you prefer, "random" (it is called "genetic drift").
More clearly, CTVT probably remained neutral for millennia, accumulating mutations that did not help or hinder its chances of survival. The team did not even find evidence that CTVT had evolved to better withstand current chemotherapy treatments, although this trend may be apparent in the future (anecdotal reports of resistance have been reported in some parts of the world). ).
In the long term, this inertia could condemn CTVT. When genetic drift occurs in a population, it often means that people will not be able to adapt to a changing world. And finally, it could well disappear completely.
But this expiry date will probably not come before tens of thousands of years, noted Baez-Ortega. We know that CTVT is declining in areas of the world where dogs are almost exclusively indoors, such as the United States and the United Kingdom, thanks to sterilization and sterilization policies and less frequent badual contact. with stray dogs in the wild. But it is still endemic in at least 90 countries.
An unresolved mystery by the team is exactly how CTVT managed to become transmissible in the first place.
"We have not found any indication of a CTVT as being an unusual cancer, genetically speaking," said Baez-Ortega. "The mutations we think have probably been implicated in the emergence and early evolution of CTVT are widespread and are well-known mutations of the" engine "of cancer that we observe in many human cancers, and we have not found anything that indicates a clear special mechanism of transmissibility. . "
This means, he added, that there is no simple explanation for why these cancers have become infectious. They obviously had to develop ways to systematically fight the immune system, but they were probably also lucky. In the case of CTVT, it could have spread because it was formed so close to the bads, making it a convenient route of transmission, and because the dogs are not very different genetically. This low genetic diversity has probably allowed cancer to survive more easily to a new host.
However, there are still more genetic clues to discover in the early days of the CTVT, which the team hopes to study afterwards.
"We would like to examine in more detail the history of CTVT and find out what its early genome and its evolution looked like during its first years and decades of evolution," said Baez-Ortega. "We are also very interested in learning more about the mechanisms by which these tumors can counteract the immune system in many types of dogs."
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