The extradimensional parasites were radioactive creatures which lived in a parallel dimension. They were able to enter another dimension through the modified technology of the Sodan cloaking devices, technology originally designed and used by the Ancients. (10.05 "Uninvited")
The extradimensional parasite was first observed in the SGC by Dr. Redden, the head of the xenology unit at Area 51, when she examined the remains of a creature from P9J-333 which had been mutilating villagers of that planet after SG-3 covertly visited them to determine if the planet had turned to Origin, the religion on the galaxy's newest threat, the Ori. She discovered that the creature was actually a docile herbivore which had been invaded by the parasite and rapidly mutated by the parasite's radiactive properties. The parasite measured a little over seven inches and was discovered in an abscessed area of the creature's stomach lining, still alive. Once Dr. Redden released the parasite from the stomach lining, it jumped at her, but Teal'c zatted it midair.
Dr. Redden concluded that the parasite was not native to P9J-333, and her statement proved correct when people on another planet being visited covertly by SG-12 were being attacked in a similar manner. This planet, P2R-866, however, had already converted to Origin, so the theory that these parasites were sent by the Priors was eliminated.
After carefully examining the missions and reports that other worlds had not been affected, Carter concluded that these mutations were happening only on planets to which the SGC had sent teams using the Sodan cloaking device. The mutations caused by the parasites happened quickly, for the cloaking devices had not been used by the SGC in the field but for a little over a week.
As it turned out, the Sodan cloaking devices emitted a radiation which the scientists at Area 51 determined was harmful to humans, so they unshielded them. The radiation was meant to keep the extradimensional parasites from breaching the subspace pocket created by the cloaking device which put the wearer slightly out of phase of his normal dimension. Without the radiation to repel the parasites, they were able to easily enter the wearer's dimension. The radiation was not harmful to the Sodan Jaffa because of the protection given to them by their symbiotes, nor to the Ancients whose physiology was slightly different than modern humans'.
Unfortunately, it was discovered that one of the modified Sodan cloaking devices was missing from Area 51. This device had been stolen by an operative of The Trust who was sent to spy on General Landry and SG-1 as they took a retreat at General Jack O'Neill's cabin on Earth. The operative used the cloak long enough for two parasites to enter local wildlife and mutate their DNA. Both mutated creatures were hunted down and eliminated, but not before innocent men, including the local sheriff, were killed by them during the area's hunting season.
- Area 51
- Priors of the Ori
- Sodan Cloaking Device
- Stargate Command (SGC)
- The Trust
--DeeKayP 18:46, 24 December 2006 (PST)