Dalek Plague

The Dalek Plague was inflicted on Earth in advance of the 2150s Dalek invasion of Earth. (PROSE: Deceit)

The Daleks caused a space plague with "plague missiles", striking Terran colonies. The only cure was parrinium which was sought by both humans and Daleks on the planet Exxilon in the Exxilon Gambit. Though the Daleks claimed to need it to cure their own afflicted colonies, (TV: Death to the Daleks) historians who later studied this era were divided on the truthfulness of this. (PROSE: The Whoniverse) Dalek-focused historians insisted the exterminators, having created the plague, were indeed unaffected. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) The Time Lords also understood that the plague, though having been initially assumed to be natural in origin, was in fact a chemical weapon attack by the Daleks designed to weaken the ever-expanding Terran empire. (PROSE: Dalek Combat Training Manual) A dissenting account claimed that the plague was merely an opportunity that the Daleks had exploited, and that they were immune to it as a result of their work in curing the Movellan virus which had earlier afflicted them. (PROSE: The History of the Daleks)

A new strain of the space plague, also effectively cured by parrinium, later also affected the Daleks themselves. The Daleks tried to invade Exxilon once again to secure all the parrinium for themselves, while the humans first brokered a deal with the Exxilons to obtain some. (AUDIO: The Dalek Protocol)

Behind the scenes
The Terrestrial Index claimed that the Daleks had inflicted their plagues on Earth in 2160 before conquering the planet in 2164, beginning a period of occupation which ended in 2167.