|Neural parasite encounted at Deneva in 2267|
|A neural parasite attacks Commander Spock|
|A neural parasite on a school chart on DS9|
- This article refers to the creatures encountered at Deneva in 2266. For other neural parasitic lifeforms, see neural parasite.
Background to the encounter
A linear progression of insanity marked the spread of the parasites through space. According to 23rd century archaeologists, the ancient civilizations of the Beta Portolan system were the first victims. In the 21st century (around the 2060s, or two hundred years before the Deneva incursion), Levinius V was attacked. After that, Theta Cygni XII, and in 2265, Ingraham B succumbed. A ship from Ingraham B next brought the parasites to Deneva colony, where after eight months of infestation the crew of the USS Enterprise managed to destroy them in 2267.
A parasite was roughly disc-shaped, about thirty centimeters in diameter and two to four centimeters in height. The edges were thin and yellowish; towards the center, the creature was thicker and redder. Occasionally, they pulsated. Parasites had no detectable external or internal organs. Spock described a parasite as "resembling, more than anything, a gigantic brain cell." Parasites were very resistant to phaser fire, even sustained and at high power levels.
Method of attack
Parasites were capable of clumsy flight. They attacked by making physical contact with a target and stinging it as does a bee. The stinger injected a strand of tissue that infiltrated the victim's nervous system very rapidly, entwining about the nerves. Leonard McCoy described this entwining as "far, far too involved for conventional surgery to remove."
Once the parasite infiltrated a host, it pressured the host to obey its commands by inflicting enormous pain. There seemed to be some level of pain even when the host obeyed, but the creature could increase the pain it inflicted to bring an uncooperative host to heel. Exactly how the creature communicated its desires is unclear, but that it could do so is evident: Spock, while infected, attempted to land the Enterprise on Deneva, despite the fact that (as he knew) this was impossible. Eventually, this continuous painful stimulation led to insanity and death.
Infected victims cooperated in working towards the parasites's objectives. This, and their enormous resistance to harm, led Spock to theorize that all of the parasites were parts of a single organism. How the parts communicated without a physical connection was not made clear. The parasites were so alien that Spock also theorized their origin was a place where different physical laws applied, outside of the Milky Way Galaxy.
The breakthrough in defeating them came when James T. Kirk, whose own older brother George Samuel Kirk and sister-in-law Aurelan Kirk had both been killed by the parasites, theorized that they were vulnerable to visible light. Clues suggested this: a Denevan declared himself "free" as his ship approached the system's sun, and the parasites remained within buildings, in shadows. Kirk's impressively high intelligence, often underrated and overlooked at least as frequently, had manifested itself to draw the inference from these clues.
The first attempt at a cure using this approach used exposure to a general of light at maximum intensity and it proved effective on killing a parasite. Spock volunteered for the next test to see if the creature's tissues could be destroyed within the body. Seeing as how the eyes of the Deneva colonist could not be shielded, Spock refused eye protection for the test and was temporarily blinded, although the foreign matter was also destroyed. Unfortunately, the test proved to be premature as analysis of the creature's remains revealed that ultraviolet light was sufficient. Initially, when Spock wrongly believed himself permanently blinded, he described the trade as "equitable" - perhaps the most cogent comment on how much pain the creatures could inflict anyone could have made. However, it turned out that Spock's inner eyelids, which instinctively came down to protect the eyes from strong light exposure, had prevented permanent damage to his optic nerves.
A constellation of 210 ultraviolet satellites was placed in permanent orbit 72 miles around the planet. The light they generated reached all parts of Deneva, destroying the entire infestation. (TOS: "Operation -- Annihilate!")