Cancer, sometimes, can be contagious


Some Cancer cells, like parasites, can enter the bodies of many hosts and live freely.As a result, they caught the attention of scientists…In humans, cancer is difficult to spread from one individual to another.If cancer cells try to move from one person to another, they are usually recognized by the body’s immune system as an invading foreign body and removed.But not all species are so lucky.Cancer cells in some animals survive in another animal and divide endlessly.So you have infectious cancer.Some of these cancers can spread not just within a species, but across species.Some cancers, even as they spread, can push a species to the brink of extinction.Generally speaking, we know infectious diseases, the main pathogens are bacteria, viruses, parasites and so on.Every time they find a new host, they take up residence in that body.If cancer cells can also move from host to host, there would be a clear difference from the human impression of cancer: each person’s cancer cells usually contain their own genes, rather than genetic information unrelated to humans or other animals.But in infectious cancers, the genome of a patient’s cancer cell is usually not its own, but from the first animal to develop the cancer.In other words, if many animals have the same infectious cancer, the genes in their cancer cells may be the same.By sequencing the DNA of a few animal patients, we might be able to trace the spread of that cancer.A Team of European researchers recently used whole-genome sequencing to find clams with the same infectious cancer in two oceans thousands of miles apart.The subject of the study, the warty clams (Credit: Alicia Bruzos & Amp;The cancers the scientists observed were described as hemic neoplasia (HN), a type of blood cancer that is not uncommon in bivalves like clams and is characterized by uncontrolled proliferation of blood cells, much like human leukaemia.Not all of these cancers are contagious.But the researchers believe they have found a contagious one.Specifically, the team traveled the shores of five European countries and collected 345 clams, all of them Venus verrucosa.The scientists gave each clam a histological examination to diagnose cancer.In eight clams, they found hallmarks of HN, a type of cancer diagnosed as leukemia infiltrating the blood vessels of the cheek and, in more severe cases, invading the digestive and gonads.The top row was from healthy (stage N0) samples and the bottom row was from patients with advanced cancer (stage N3).B is the healthy haemolymph, which is filled with normal blood cells. C is the haemolymph occupied by cancer cells.Of the eight clays with cancer, three came from the Atlantic coast, northwest of the Iberian Peninsula, and five from the Balearic Islands, off the Mediterranean Coast, separated by more than 1,000 nautical miles (1,852 kilometers).The diagnosis was only the first step, confirming that they had the same type of cancer. To know if it was the same type, genetic sequencing was needed.If the DNA of a cancer cell and a normal cell in a clam is significantly different from that of the same animal, it suggests that the cancer cell probably came from another animal rather than its own.Since it was blood cancer, the samples for sequencing the cancer cells were taken from the haemolymph of the clam;The healthy cells in comparison were taken mainly from the feet, where it is harder for cancer cells to invade.Of course, there are normal cells in haemolymph and cancer cells in feet.The scientists first sequenced mitochondrial DNA.They were surprised to find that the DNA sequence of another species, Chamelea Gallina, was detected in the haemolymph of six out of eight clams.Among them, the 4 most sickly clams were mostly derived from the chicken clams, but few belonged to the clam clams themselves, probably due to too many cancer cells in the hemolymph.In contrast, the feet had a higher proportion of normal cells, and more sequences of the clam itself were measured.Mitochondrial DNA sequencing analysis of clams verticillata with cancer showed that the left column was from hemolymph and the right column was from feet (with few cancer cells).Red is the DNA sequence of the clam, blue is the DNA sequence of the clam.The haemolymph of the four sickest clams contained almost all foreign sequences. The two least sickest clams did not detect foreign DNA from one animal, but had sequences from two animals. The cancer cells in these clams were most likely foreign.No foreign sequences were found in the mitochondrial DNA of the remaining two clams.They were the two that scientists had diagnosed as being less ill, perhaps because of low levels of cancer cells in the haemolymph.In addition, DNA sequencing in both the mitochondria and the nucleus showed that the foreign DNA sequences were so similar between the six clams that scientists believe they were infected with the same type of cancer.The team also believes the clam is spreading the cancer across species.In the Mediterranean, there is a high degree of geographic overlap between the clams.Scientists build genetic trees based on the sequencing of mitochondrial DNA.Foreign DNA sequences were highly consistent among the six cancerous clams, and were similar to those of the cockles, as shown by the black dots.The normal relationship between the six clams is not that close, as shown by the white dots. When the cancer cells divide in a clam’s body and are expelled from the body, they can survive in seawater.When you encounter another clam, re-infect it and kill it.That’s how cancer spreads.As for how it spread thousands of miles to another sea, Alicia Bruzos, a co-author of the study, said, “It could be human shipping that carries the cancer from one area to another.””Oldest Cancer” Actually, infectious cancers don’t just occur in Marine life, and they don’t just occur in invertebrates.Some land mammals, closer to home, also suffer from these diseases.In 1876, a Russian veterinarian named Mstislav Novinsky discovered a particular kind of cancer in dogs: he infected one dog with tumor cells from another, which gave rise to tumors.The cancer is called canine Transmissible flower willow tumor (CTVT), and as the name suggests, it can be spread sexually, mostly on the genitals.Being able to spread means it doesn’t die with a dog, making it “immortal” in a way.But for a long time, humans did not understand how it spread.Scientists have debated whether a virus spreads cancer, or whether the cancer cells themselves spread the disease.Until 2006, when a team of researchers at University College London put an end to the dispute.They collected naturally occurring CTVT tumors and blood samples from 40 dogs on five continents and examined the DNA of tumor tissue and normal tissue.It turned out that tumor samples from all over the world contained some of the same genetic markers that were not present in normal tissue.This led scientists to conclude that CTVT, a type of cancer, is spread by the cancer cells themselves.A cancer cell in one dog, sexually transmitted, infected a second dog, a third dog…Even after the original dog is gone, cancer cells with its DNA can live on in other dogs.Another study in 2014 found that CTVT appeared in dogs 11,000 years ago.It is the oldest known form of cancer living on earth.Today, the cancer has spread around the world, and every dog that catches it still carries the DNA sequence of its first victim with it.The picture shows husky.A 2014 study concluded that CTVT originated in an ancient dog, close to today’s Alaskan malamute/husky mix (GdML), but that while the effects were widespread, it was at least curable with chemotherapy.In contrast, another infectious cancer in mammals, arguably more aggressive, nearly wiped out a species.The Tasmanian devil, also known as the Tasmanian Devil, lives on the Australian island of Tasmania.Among them is a cancer called Tasmanian devil facial tumor disease (DFTD), which is spread by biting.It’s a lot like zombies in the movies, where you take a bite out of a living person’s face, and that person gets infected and turns into a zombie.For a tasmanian devil with DFTD, the tumor may start as a small lump in the mouth, then grow into a large tumor on the face and neck, and even spread to other organs.Disfigurement isn’t the worst of it. When facial function is disrupted by tumors, tasmanian devils’ ability to feed is severely reduced and they can easily die of starvation.Tasmanian devils with DFTD have a nearly 100% chance of dying within 12 to 18 months.This type of cancer was first identified in 1996.Between 1996 and 2015, the tasmanian devil population plummeted by 95 percent.It was listed as an endangered species in 2008 and is also protected by the Australian government.Today, however, the species remains endangered, with fewer than 25,000 estimated in the wild.Fortunately, with the exception of dogs and tasmanian devils, victims of infectious cancer are rare among mammals.Is human cancer really not transmissible?Often, one person’s cancer cells are easily killed by another person’s immune system.However, in certain circumstances, there are still conditions for cancer to spread.In one case, the mother has cancer during pregnancy.Cancer cells could then spread from mother to fetus, or from twin to twin.Another is organ transplants, where patients are often given anti-rejection drugs to keep their own immune systems from attacking another person’s organs.If a donated organ contains cancer cells, it can spread cancer.Medical devices can also be dangerous to patients if they become contaminated with cancer cells.For example, during surgery, the skin, the body’s largest immune organ, is destroyed, giving foreign cells an opportunity to invade. At this time, if someone else’s cancer cell is on the surgical instrument, it may enter the patient’s body.So we are not completely safe from the spread of cancer.But compared with the clams that were harmed by blood cancer, the truly infectious cancer is at least not a threat to humans.By the way, when the researchers found that the clams cancer came from the clams, they went back to the same area along the Mediterranean coast and brought back 200 clams.The diagnosis was that none of them had cancer.Scientists say clams may now be immune to this type of cancer.Warty clam: what about trust between clams??The original papers: https://elifesciences.org/articles/66946 reference links:https://pubmed.ncbi.nlm.nih.gov/16901782/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3918581/https://web.archive.org/web/20050921014142/http://www.dpiwe.tas.gov.au/inter.nsf/WebPages/LBUN-5QF86Ghttps://www.theguardian.com/world/2015/dec/30/tasmanian-devils-can-catch-second-strain-of-facial-cancer-say-researchershttps://www.abc.net.au/news/science/2021-05-27/tasmanian-devils-give-birth-in-semi-wild-sanctuary-on-mainland/100169686https://slate.com/technology/2021/10/contagious-cancers-warning-humans-climate-change-environment-zombies.html

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