Purge of the Zersoa System

The Purge of the Zerosa System was a lamentable purgation campaign that was carried out by the military forces of the Imperium of Man, following the failure of the Emperor's Trident Chapter to halt the machinations of a marauding Death Guard warband, which managed to successfully unleash several virulent plagues that spread throughout the system. Following several dozen outbreaks, the Imperium was forced to purge the entire system of life to half the spread of the virulent plagues.

History
The Emperor's Trident 3rd Company answered a distress call from the Zersoa System. As the Astartes company entered the system their ship, known as the Solar Harvest, was immediately attacked by an unknown enemy, heavily damaging their vessel. During the void battle the Solar Harvest was boarded and the 3rd Company finally knew whom the true foe was - Plague Marines of the vile Death Guard Traitor Legion. The 3rd Company ship had to tactically withdraw to a nearby asteroid field in order to re-group and make some immediate repairs. They managed to take refuge in a nearby destroyed mining station, utilising it to evade the Death Guard's vessel that hunted them. Here, the 3rd Company attempted to effect repairs of what they could in order to deal with their unwelcome guests. What happened next were weeks of void combat, with several boarding actions taking place between both ships. Eventually, the Death Guard ship finally withdrew from the system, their nefarious plan carried out to fruition. The system was corrupted by the long-reaching tendrils of Grandfather Nurgle, which was soon beset by various vile plagues of both Nurgle's Rot and other plagues which killed tens of millions of Imperial citizens. Due to their failure to half the Death Guard's plans, the Imperium was later forced to launch a system-wide purge of the Zersoa System and cordoned it off from the wider Imperium. It was later declared Perdita ('Forgotten') by order of the High Lords of Terra.