Codex: Chaos Daemons (2008), p38 — Nurgle's Rot

Chief among the many gifts that Father Nurgle has granted an ungrateful galaxy is Nurgle's Rot. It is his masterpiece - completely incurable, highly infectious and with a very, very slow course. These characteristics allow it to spread uncontrollably, overwhelming whole continents, planets and star systems.

And that is not all. This perfect illness does not kill its host quickly; rather it slowly turns the victim's body into a bloated, rotting, living corpse. At the same time it erodes the victim's soul. It painfully corrupts it to the point where the tortured victim has to choose between the only two routes left open to him. He can either end his own life, or he can fully embrace the ways of Father Nurgle, predelicting in contagion and putrescence, revelling in buboes and sickness until death puts an end to his suffering.

Only then will he realise the true blessing that has been visited upon him, as his soul is reborn in Nurgle's realm, in the immortal shape of a new Plaguebearer.