Chaos plague

From HammerWiki

At the start of the Age of Reckoning, a virulent disease known as the Chaos plague is infesting citizens of the Empire.

Victims of the Chaos plague first experience tiredness, aching, soreness and extreme thirst, followed by bouts of nausea. The final stages of the disease only appear after about a month of sickness, at which point the victims start to transform into fiendish mutants and attack anyone in their vicinity.

As the plague spreads throughout the lands of Empire, despite quarantines and martial law, the city militias are overstretched trying to deal with the hordes of Chaos mutants roaming the streets, causing law and order to break down. Bandits and brigands appear to terrorize the countryside, and refugees flock to the few remaining areas of safety.