Tasmanian devil cancer infection continues unabated

Bad news if you're a Tasmanian devil. Devil facial cancer continues to spread through the population and threaten its future.

It is home to three scientists and a veterinarian. cambridge university Reports new evidence contradicting results published in 2020 suggesting tumor transmission in Tasmanian devils is slowing (reference). The three scientists repeated research published by a previous team. washington state universityAnd they discovered they had made an error that led to incorrect predictions about the future of the endangered Tasmanian devil.

tasmanian devil, Sarcophilus harrisii, A small, very smelly, and very noisy marsupial that once lived throughout Australia, it became extinct about 3,500 years ago, probably due to hunting by dingoes.

The Tasmanian devil, as its name suggests, currently lives only on the small island of Tasmania, where there are no dingoes. This nocturnal black marsupial makes its living primarily by scavenging rather than hunting, preferring to feed on roadkill and leftover carrion. Their keen sense of smell makes them very skilled at finding carrion and rotten flesh in the dark.

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Tasmanian devils are not picky eaters and will happily eat the carcasses of animals they smell, including insects, amphibians, reptiles, birds, and mammals. Their powerful jaws and specialized tooth structure allow them to eat bones, fur, and exoskeletons.

Tasmanian devils have a very short lifespan. In the wild, healthy, disease-free devils can live up to 5-6 years, but captive individuals can live as long as 8 years.

The Tasmanian devil is officially listed as an endangered species (population in decline). IUCN Red List, primarily threatened by a contagious cancer known as Tasmanian devil facial tumor 1 (DFT1), which causes visible symptoms (rapidly expanding facial tumors) known as devil facial tumor disease (DFTD). ) causes. Because these tumors are located on the devil's face, they often cause starvation. DFT1 killed over 60% of the entire population.

Contrary to what most people think they know about cancer, contagious cancer is actually contagious, and as an undergraduate microbiology student before spending two years in cancer research, I focused on this feature. These cancers are spread from person to person by metastasis of living cancer cells. As you might imagine, contagious cancers are extremely rare in nature. Only three contagious cancers have ever been identified in mammals, two affecting Tasmanian devils and one affecting dogs.

Cancer itself is the result of uncontrolled cell proliferation that leads to the formation of a tumor. This runaway growth is caused by mutations in one or more genes involved in controlling cell division or cell death, causing affected cells to divide madly or become immortal. Cancer-causing genetic changes can occur through environmental factors (such as smoking, sunlight, and chemical exposure, to name a few) or through the inheritance of defective genes.

Transmissible cancer in Tasmanian devils is of great interest to many cancer researchers and conservation biologists alike, because, as previously suggested, cancer is rarely transmissible. In the case of Tasmanian devils, cancer cells spread during fights such as bites on the face or neck. This is a common behavior among devils, who often compete over mates and food.

Previous research (reference) identified a single DFT1 “founder devil” in the 1980s and used genomic data from DFT1 tumors to create a family tree tracing the lineage of this contagious cancer back to its origins. (Figure 2). Then, using phylodynamic models, a method that maps the genetic history of a pathogen's ancestors, the 2020 study estimated cancer epidemiology parameters and predicted its future trajectory.

Since its emergence, DFT1 has spread throughout almost the entire Tasmanian devil population, and the species was listed as endangered in 2008 due to the rapid decline in devil population density caused by DFT1. According to 2020 statistics, the population decline rate is decreasing over time. Modeling studies predicted that cancer would persist at low densities within the devil population but would not increase.

This process is known as endemicity.

However, in replicating the 2020 study, the Cambridge group conducted a more extensive genotyping analysis of DFT1 cancer cells to estimate its spread. In contrast to the 2020 study, the Cambridge research group found no evidence that the spread of DFT1 in demonic populations was slowing. They found that researchers in the 2020 study made this mistake because they did not read enough DFT1 sequences to accurately gauge the spread of the disease, resulting in incorrect conclusions. He suggested that this may have been the case.

The Cambridge research team therefore believes that DFT1/DFTD is still occurring and widespread, and therefore remains a significant threat to the survival of the Tasmanian devil.

sauce:

Maximilian R. Stamnitz, Kevin Gori, and Elizabeth P. Murchison (2024). There is no evidence that contagious cancers have transitioned from emergence to endemism in Tasmanian devils., Royal Society Open Science | Doi:10.1098/rsos.231875

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