Spores are subtle infestation agents devised by the zerg. Before the zerg invade a planet, their fleets typically drop a massive payload of these spores onto a world's surface. These spores spew a flood of creep, initiating infestation.
Terran Confederacy scientists discovered a zerg outbreak in a string of Fringe Worlds. They conducted experiments with their discoveries in the secret Fujita Facility on Vyctor 5, as well as in the Ghost Academy on Tarsonis. They were able to use the spores to grow creep.
The Terran Confederacy conducted experiments with zerg specimens in the secret Jacobs Installation on Mar Sara. They hid ardeon crystals, tainted with the spores, deep within the facility and went to great lengths to protect them.
After the destruction of Mar Sara by the protoss, the planet was quickly resettled by the Kel-Morian Combine. When they attempted to excavate the Jacobs Installation, the Dominion quickly stopped them, hiding the reasons behind level Black censoring and hiding the facility itself in a dead spot.
Terran Dominion Thor pilot Sandin Forst and his two companions heard rumors that extremely valuable ardeon crystals could be found inside the facility. They broke in, and Forst, the sole survivor, began collecting them from a vault, but the spores very quickly transformed him into an infested terran. The Confederacy had gone to great lengths not only to keep people out of the vault, but to keep people from leaving as well. Even his Thor could not break him out, and Forst was trapped by the wreckage of the vault's roof.
Second Great War
The Raynor's Raiders discovered an infestation sweeping through refugee camps on Meinhoff, such as that of the former colonists of Agria. The infested colonists created by the virus were vulnerable to the star's high UV output during the daytime. Matt Horner described the infestation as a "new trick" and "virulent." Agrian colonist Dr. Ariel Hanson began working on a cure.
During the End War, the fallen xel'naga Amon unleashed an infestation upon the terran worlds of the Koprulu sector. Allied commanders held off waves of infested to evacuate the Kel-Morian Combine colony lead by Debra Greene, and helped Terran Dominion Lieutenant Rosa Morales purge a fringe colony of its infestation before it overran the planet.
Sometime before the Defenders of Man Insurgency, an outbreak of zerg infestation occurred on the Umojan Protectorate colony of Jarban Minor. Nova Terra and her Covert Ops Crew arrived along with the Tal'darim, fighting through the infested to reach the terrazine the Umojans were harvesting from the local Jarban gliders.