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Praxeus was a bacterial pathogen originally designed to target plastic particles. However, it became a fatal disease that was able to infect beings with plastic inside them, such as humans containing microplastics or animals that consumed plastic waste.
When a humanoid was infected, their skin developed pale cracks across it, eventually overwhelming the body. Once it had infected the victim's entire body, they would disintegrate into a cloud of dust It could be spread when contact was made with open wounds and between species. Human astronaut Adam Lang became the first and only known survivor of Praxeus, due to a cure derived from bird enzymes. The Thirteenth Doctor was able to replicate the cure using her TARDIS and spread it across the Earth's jet streams, halting Praxeus on Earth. Though Suki Cheng alerted what was left of her race to the cure, the Doctor stated that it was designed for humans only and might have disasterous effects on another race. This proved true as when Suki used the cure on herself, it rapidly accelerated Praxeus' effects, killing her in seconds. (TV: Praxeus)