Will the devils survive?
The increase in the infection of marsupial devils with infectious cancer has decreased
Researchers note that among Tasmanian marsupial devils, the number of infections with a deadly disease that threatened to completely destroy this animal species has decreased (see the press release of WSU Tasmanian devils may survive their own pandemic - VM).
Facial cancer of marsupial devils (devil facial tumor disease, DFTD) is one of the rare oncological diseases that can be transmitted from body to body. It was discovered in 1996 and has since killed almost 90% of Tasmanian marsupial devils. Among them, cancer spreads through bites during fights between males during the mating season. Sick animals die within six months. By origin, the cells of the Tasmanian devils facial tumor turned out to be mutated Schwann cells — auxiliary cells of nervous tissue that are located along the long processes of neurons, forming an electrically insulating myelin sheath.
By now, there are only about 15 thousand marsupial devils left. But the researchers note that the exponential growth of the disease among them has stopped. Now the infected devil transmits the disease to no more than one of his relatives. This means that over time, the disease may disappear altogether.
Earlier, cancer geneticist Elizabeth Murchison from the University of Cambridge and her team analyzed the genomes of more than 600 tumors collected between 2003 and 2018, and found five genomic versions, three of which are widespread, and some devils were infected with several types of tumors. According to a study published in PLOS Biology, this detail may complicate the development of a vaccine to fight cancer.
Later, geneticists from the University of Washington Andrew Storfer and Austin Patton examined how the genomes of tumors changed over time. They focused on 28 genes that appeared to evolve at a constant rate, and tracked how specific mutations spread in tumor samples. This allowed them to conclude about the rate of cancer spread among marsupial devils. As reported in an article published in Science, at the peak of the epidemic in the early 2000s, each infected devil transmitted the disease to at least 3.5 others, but recently the transmission of the disease has slowed down and some infected animals do not infect relatives at all. Storfer and Patton cite possible reasons for this reduced population density, improved immune system in the remaining devils, or changes in their behavior.
In this regard, researchers warn against plans to introduce captive-bred individuals into natural populations of marsupial devils. If the population density increases again, transmission of infection will also increase. And animals raised in captivity may lack the stability developed during evolution in the wild.
The link between the spread of the disease and animal behavior is confirmed by a study published recently in the journal Proceedings of the Royal Society B. Rodrigo Hamede and David Hamilton from the University of Tasmania monitored the behavior of 22 marsupial devils using radio collars for six months, assessing, in particular, the number of contacts with relatives. They found that after infection and the development of the disease, the devils began to avoid meetings with other individuals.
Portal "Eternal youth" http://vechnayamolodost.ru