Red Rust is a virus developed by the treacherous medic Pharma. Once infected the patient is infected, the virus lies dormant until they change form. The their bodies start falling apart. Their optics corrode and drip down their faceplates, then everything goes, total liquefaction, every hinge, pivot and piston until total Spark Collapse.
Infected:
Fiction
IDW Generation 1 Continuity
More than Meets the Eye
Pharma developed the bomb for his own gain. By infecting all the patients of Delphi with a Sound Bomb, the combined alternate form of the Decepticon Genericons, Sonic and Boom, and letting them die, he had a constant supply of Transformation cogs. Transformation cogs that, Tarn, Leader of the DJD would keep paying him for. Life After the Big Bang