Spore

Zerg spores are subtle infestation agents devised by the zerg.

Vyctor 5
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.

Chau Sara
The Overmind subtly seeded the soil of Chau Sara with hive spores. Eventually the zerg more openly infested that world.

Mar Sara
The Terran Confederacy conducted experiments with zerg 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 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.