Deadly, emergent cancer becoming endemic in Tasmanian devils
An emergent transmissible cancer that once threatened Tasmanian devils with extinction appears to be transitioning to a state of endemism, researchers report. The findings of the study, which used an epidemiological phylodynamic approach to reveal the pattern of emergence and spread of the disease, bring hope for the continued persistence of the iconic species.
First discovered in 1996, Tasmanian devil facial tumor disease (DFTD) - a fatal, transmissible form of facial cancer - is found across 95% of the animal's geographic range and is estimated to be responsible for a species-wide population decline of 80%. Emerging infectious diseases like DFTD are among the primary contributors to species endangerment and have led to species extinction. Recently, phylodynamics has become an important tool for characterizing the epidemiological parameters of rapidly evolving, emergent pathogens and has become notable in its application to understanding novel human viruses, including SARS-Cov-2.
However, its application to nonviral pathogens has been limited by the challenges associated with their larger genome sizes. DFTD, for example, has a genome thousands of times larger than any virus. Despite initial predictions that DFTD would lead to the extinction of the species, Tasmanian devil populations persist - and may even be recovering - in long-diseased areas.
To better understand this discrepancy, Austin Patton and colleagues applied phylodynamics to characterize the epidemiological history of DFTD. Patton et al. discovered that DFTD is becoming endemic in Tasmanian devils and is exhibiting a pattern of transmission rate decline. The findings suggest that, if left to evolve naturally, DFTD may go extinct or even coexist in devil populations; either way, devil extinction is unlikely, they say. What's more, the study demonstrates that phylodynamic studies need not be limited to viruses and can be applied to a wide range of other emergent pathogens across species.
