From WoWWiki

Plague Eruptors are creatures that can be encountered in the upcoming WotLK expansion.

Plague eruptors are the latest experiment of the Lich King, designed to spread horror and chaos across the world of the living. These walking corpses have quickly earned a reputation as the most destructive of the Scourge army: hyper-violent, incredibly strong, and deceptively fast. The most terrifying weapons in the eruptors' arsenal are the myriad pulsing nodules that dominate their rotting skin. It is from these nodules that the undead plague festers and bursts, insuring that wherever the eruptors go, they quickly spread the Lich King's apocalyptic contagion.

Speculation

This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore!

It is speculated that these are the new type of Abomination.