It seems that while I did a work up of the Neural Parasites for my game I never got around to sharing it here...

Let me rectify that error.

Neural Parasites/Bluegill
The Neural parasites are an insidious species that infect a host body with the aim of taking full control, completely subduing its memories and personality. This host body is then supercharged as the parasite has a far more active control over the host body functions, with increased adrenalin and healing the host becomes stronger and tougher, while their mental attributes are completely replaced. For its part the Parasite has the ability to leave the host anytime that it requires and seems to care nothing for the 'meat' host.

Biology
The parasites' natural appearance resembles that of a large light purple, crawling insect. This creature then tries to enter a living being as a host body. The parasites prefer higher level beings in order to facilitate their agendas, but they are able to infect lower animals. A lifeform inhabited by one of the parasites displays a noticeable spine-like protrusion from the base of the neck that appears to permit the parasite to breathe. The Parasite will wrap itself around the lower brain stem/spinal column and take direct and full control of the host body, trapping the mind within as a mute witness to its actions. The parasite share several characteristics with the Trill, and the host will show increased isoboramine levels similar to that of the joined Trill.
They are apparently incapable of inhabiting artificial lifeforms. It has not been discovered if the parasites are limited to any specific host biology’s (to date they have only been encountered infesting hosts within the human range of biological tolerances * ), other lifeforms such as the Horta or Changlings may be immune.
*In the DS9 relaunch it is established that the Parasites are unable to infest Cardassian biology.
The parasites seem to be formed around a local hive mind, connected to a queen, who often is the core being and works towards the infiltration goal. Although Parasites can detach themselves from this hive mind at will and work as an individual.
The parasites appear to be highly intelligent, perhaps more intelligent than Humans, and even display aspects of higher culture, such as a love of theatre. The parasites seem incapable of retaining either some or all of a host's memories, and while the Parasites have become expert at piecing their hosts life together, sometimes gaps in the parasite knowledge may exist that would give it away to anyone sufficiently knowledgeable of the host individual.
A Human inhabited by the neural parasites will display increased physical strength, reflexes and stamina. Even beyond the physical limitations of the host body, even the host's resistance to energy weapons is increased, it is thought that the host body also enjoys increased healing to compensate for any damage caused. A host will appear physically healthy, but most often the controlling parasite will keep the full extent of the increased physical prowess a secret until it needs to defend itself... It is often easier to kill a host than to save them as Phasers need to be set to kill levels and there is no guarantee that the host will survive.
The parasites are connected to a mother organism via a hive mind, a larger creature likewise capable of inhabiting a humanoid host. The matriarch organism will have infected its host to a massive degree with significant tissue replacement and by this time the host is all but dead, the meat shell kept alive only by the Parasite. The death of the queen will defiantly kill the host. The death of this creature seems to result in the deaths of all progeny, and will free all connected hosts.
If a queen is not discovered or parasites are working individually, the host may be freed from their parasite only by dangerous surgery, which due to the location of the parasite on the brain stem is more likely to kill the host. The Parasite may choose to evacuate its host at any time, usually escaping via the throat and mouth, this will cause massive trauma to the host, but if medical attention is on hand, odds of survival are good.

History.
The neural parasites were (historically) first encountered by the Federation in the 23rd century on a comet near Trill, by then head of Trill Symbiosis Commission Audrid Dax, whose husband was a victim of a parasite, accompanied by Christopher Pike. However, the Trill authorities classified the knowledge and never released it to public, and Starfleet Command agreed to classify Pikes reports in support of the request by their allied world.
This top secret classification nearly proved to be Starfleet’ undoing as the next encounter was over 100 years later when Neural parasite aliens attempted to infiltrate the Federation's Starfleet Command in 2364, by physically infiltrating high-ranking admirals within the organization. Persons who fell victim to infiltration included Admirals Gregory Quinn, Aaron, and Savar. The parasites were thwarted in this attempt to take-over and infiltrate Starfleet command in 2364 by the actions of Captain Picard and the crew of the USS Enterprise NCC-1701-D, leading directly to the death of the hive queen infesting Commander Remy.
As a result while the existence of the Parasites remains classified and secret from the general population it is however a situation that has been briefed to senior Command Officers and Starfleet Medical to help ensure that such a covert take-over cannot be repeated
In 2376 it was revealed that the Parasites had attempted to infiltrate the Federation again, through the infection of First Minister Shakaar Edon who was assassinated upon ratifying Bajor’s membership into the Federation, the subsequent investigation revealed the Parasites involvement and Shakaar’s infestation, but not their plan, although it seemed that they had planned to spark a civil war within the Federation perhaps with the aim of weakening it. It also revealed the many biological similarities with Trill symbiosis, although the physical location of the parasite, and control of non-Trill hosts along with total control of the host body were striking differences, this lead to many leading questions being asked of the Trill representative to the Federation, and a serious questioning of their secretive nature…
It was later revealed by ancient Symbionts in the pools of Mak’ala that the neural parasites were in fact genetically created from Trill Symbionts, who had been sent to an ancient Trill colony on Kurl; these symbionts had been engineered specifically to allow them to move between hosts without killing the host to be passed from Trill to Trill. The colony was quarantined and eventually annihilated by the regular Trill when it was discovered that the fatal combination of a mutated virus and genetic engineering had sent the symbiont’s violently mad. The few surviving Parasites that had escaped this destruction swore revenge against the Trill and slowly bided their time to reap it.

Bibliography;
Star Trek TNG episode: Conspiracy
Star Trek DS9 Novels;
The Lives of Dax
Mission Gamma, book 4; Lesser Evil
Worlds of DS9, book 2; Trill


Results of Parasitic infection.

As players are unlikely to play an infested host, these stats are for NPC’s only, they would need to be balanced if a player wanted to actually ‘play’ this as a character…
. Completely replace mental attributes of the host Intellect =3, Presence =2
. Increase host fitness and coordination by 1 and Reaction and Vitality edges by +1
. Hive Mind to local 'queen'. (Psi 1. Hive Mind 1*) Effectively localized, limited telepathy to the hive…
. Advantages; Toughness +2, Increased Healing +1, Strong Will +1, High Pain Threshold +2
. Disadvantages; Species Enemy; Trill Symbiontes -3, Dark Secret (Parasite Infestation) -3, Fanatic (Protect the hive and queen, advance the plan) -2, Amnesia -1 (Hosts personal life).
- Host is immune to stun effects on Phaser and most phasers must be set to at least low level kill. Unless it very close quarters this will result in the host being stunned, close range will deliver the full effects and most likely kill the host.
Host keeps the keys skills to help infiltration, but it is recommended that any non-essential skills are removed