The Shepherds of Rot are a band of beasts and drovers who roam the Vale of Efengie searching for Nurgle's favoured pets. They were formed under the leadership of the good-natured (but obnoxious) Larvulous, Gadfly of Nurgle, who disappeared shortly after the founding, presumably dispatched to spread the good word elsewhere.
Shortly after Larvulous' disappearance, his lieutenant Wex the Pustulent assumed command of the Shepherds. Wex takes a more hands-on approach to tending Nurgle's garden, seeing fit to create abominations of his own rather than just be a caretaker of Grandfather Nurgle's.
Here are some more pictures, close ups of the models in the group shot above, and also a few models who aren't in the group shot.
Poximus - an overzealous plaguebearer who had been assigned to Larvulous' command, but now follows the Shepherds.
Leish Maniasis - a chaos warrior who cares for his two plagued hounds (Mange and Flybait).
Antethrax - Wex's closes lieutenant, he leads the other chaos warriors.
The Bloat - a massive chaos warrior kept alive only by Nurgle's favor.
Tallpox - a plaguebearer mangled by Wex's poorly cast summoning spell.