Apostles of Contagion
Formerly of the Death Guard chaos marine legion, the Apostle of Contagion are a warband of demented nurglites following their rotting master, the Chaos Lord Necrosius (an apothecary turned sorceror), who believes that Grandfather Nurgle's gift of eternal life must be freely given to all in the galaxy....barring mention of course that this form of eternal life is as an unwashed zombie but then what did you expect from a gang of pusbags?
Having broken off from their former brothers, the Apostles follow only the will of their mad lord and bent their knees to their putrid god. Due to the fact Nurgle's gift is for all, they don't care if they infect imperial or fellow chaos worshipper alike with the zombie plague, leading them to having quite a few enemies.
They bear a hatred for Typhus, the Herald of Nurgle, and his band of chaos marines. It is stated the reason for this was the Herald's betrayal of the Death Guard which sent them into damnation but since they seem to enjoy damnation so much now...in a way the hate has no real logical reason beyond the obvious of a rival champion of Nurgle for another. As they say, there can only be one!
The Apostles were responsible for the widespread zombie plague outbreaks that occured on the world of Vraxs and are so partly responsible for the corruption and fall of that world.