From 1d4chan

Plague is the generically named alien zombie army of Warpath. Introduced in Deadzone, they are a mix of Tyranids and Genestealer Cult. They were featured in the original Deadzone two-player starter box, but were expanded into a full army in Warpath in third edition.

Aesthetically they are mostly zombified human forces, but do have a selection of large alien monsters to compliment these forces. On the tabletop they are the most melee combat oriented of the factions. This can be contrasted with the Veer-Myn; both are horde armies, with the Plague being focused on melee and monsters, while the Veer-Myn are focused on shooting and vehicles.