Poxwalkers are born of a particularly insidious contagion sometimes called the walking pox, a disease that does not simply kill its victims but claims them body and will. Those infected sicken, waste, and die, only to rise again as shambling husks, their minds burned away and replaced by a single dim compulsion: to spread the plague that unmade them. They feel nothing, fear nothing, and cannot be reasoned with or turned back.
What makes the Poxwalker horde so dreadful is its capacity to grow. Every mortal they wound with tooth, nail, or filth-caked hand risks catching the same curse, and the newly slain soon lurch upright to join the throng. A modest outbreak can consume an entire hive-city in days, transforming a thriving population into a groaning ocean of the infected that batters mindlessly against the survivors' defences.
On the battlefield the Death Guard herd these wretches as expendable fodder, sending them forward to absorb enemy fire, choke chokepoints, and drown defenders in sheer weight of rotting bodies. Individually feeble, in their teeming multitudes they are a weapon of terrifying attrition, and a grim testament to the generosity of Nurgle, who wastes nothing and finds a use even for the dead.