Brain Worm

Brain Worms are a dangerous parasite bred for one purpose, to take over a host and use it to further the hive of their kin. Originally created in the Middle East, it has spread to a few other regions along the Silk Road & just beyond. Hives of them are centred round a single queen, a larger bulkier female while all others are hermaphrodites. Speculation sems to point to an ancient origin where parasitic worms of many animals were intermixed with the use of magic to create the first brain worms.

Transmission & Vectors

Most victims are affected by these parasotes in waterways or deliberate implantation. Quite a few have escaped into the wild and through laying eggs in their victims bodies that are excreted out through solid waste make it in to fresh water based waterways. A few times an evil creature & it's henchmen, or elements of a hive, will deliberately infect victims to expand the reach of these, The latter though can only really be achieved in warmer climated due to the cold inhibiting the grow of the eggs & larval stage.

Causes

The worm's larva or eggs will usually be found in untreated or improperly treatted water that is swallowed by the victim. There, it will react with the stomach acid, devloping a covering of hydrocarbons to protect itself from being broken don by digestion. Thjis causes it to start growing large enough to allow it to become mobile. When it enters the intestines, it will enter the bloodstream through the intestine walls making it's way to the brainstem where it will latch on with it's sucker-like mouth & needle teeth to the surrounding tissue releasing a nukmbing agent to avoid alerting the victim. A thin tongue filled with nerve ending slides out of the mouth when stabilised wrapping its way around the based of the brain pushing itself on in. There the nerves of the tongue starts to wire itself directly into the brain allowing it to interact & eventually take over control of the brain.
This usually takes 1 week to 1 month depending on the complexity if the animal's brain and size. It is also noted that if the worm is adult size it can live in the water itself, and if no eggs or larva are present can take over a host itself. This is done by turning the teeth it hass out of the mouth and effectivelly gnawing it's way through the back of the mouth or the externally exposed part of the throat.

Symptoms

The host will appear drunk or suffering from type of neurological damage or ailment from there on until dealt with. These appear much much worse initially, and can be mistaken for lack of oxygen drom swimming underwater too long, or any other cause. These came down quite a bit but those who knows the creatuer affected, will notice a change of character afterwards. They seem to crave being near bodies of clear fresh water, and constantly swimming in it. All the while the larvae are likely being excreted out. If there is no other brain worm detected in the area of 5 miles, picked up by the use of phermones detected in the water or in the air using the victim's olfactory senses, then the worm develops into a queen. Otherwise they appear to take on a strange out of character personality wanting to stay with others who are affected.
The queen will self impregnate while still in the standard form being an hermaphrodite, and will pump out as many eggs into the victim's bloodstream to pass back into the bowels & excreted. Her form can grow to twice the size and put pressure on the victim's throat and the back of the skull. A buldge is noteable at times depending on the size of the carrier.
After a few months (iusially 6 to 9 months), she will try to get the host to enter the waterway and drown themselves. Here, she will exit the body and feed on it to produce far more larvae.
Any other hosts will generally follow the queen who uses phermones to direct the others and try to take over & dominate the region they are in. They become insular and try to infect others who pass through it, and a few will travel to other regions nearby to spread the worms further. Usually the intial infectoin will die out shortly after spreading due to no further hosts available going dormant until it is reopopulated.

Treatment

There is no proper known treatment though high doses of poison can be recommended to force the worm out. The problem with this is that it could eaasily kill the host, and if not got early could leave the host brain damaged as a result. The only successful method seems to rely on the use of magicf by spellcasters or divine favour through a cleric. And these may still carry some risk.

Prognosis

Unfortunately since cutting the worm out leaves parts still in, mainly the tongue, and poisons can be fatal for the host too, there is not much others can do. Those left with it will eventually die after their basic survival instincts are dampened by the worms. Magic & divine favour are the safest and seem to have the best results.

Sequela

Severe brain damage, a lack of free will, and malnourishment are the three leading problems caused by the worm. The host generally lacks the free will to look after themselves & any dependants. Also if not treated quickly with magic, the central nervous system & especially the brain is damaged beyond recognition. This is caused by the worm's tongue growing longer & larger linking to more nerves.

Affected Groups

Settlements of different sizes can be affected but generally those in warmer or hotter climes are worst affected. Both The surface world & the Underdark suffer equal chance of being affected, with regions near Mindflayer controlled areas suffering worst than others. Usually the smaller more primitive groups of sentient creatures are affected worse, along with those relying on freshwater courses such as rivers & lakes. Most large towns & cities can easily have a small core group of the worms though they conversely have a greater chance of detecting them and spotting those affected.

Hosts & Carriers

Sentient creatures are generally favoured as the worms can interface better with these creatures brains & learn to. Though saying that, any creature of sufficient size to be took over the worms find that creatures of Dwarven & Gnomish size up to the size of Goliaths are favourable due to these crearures being much moer common, and usually of high enough intelligence. The worms can learn and reports come in that the queens supposedly pass on some type of genetic memory from her host to her young.

Prevention

The only way to prevent being infected is the killing of the worms & their larvae & eggs. That and the destruction of any habitat they thrive in while outside the body. This prevents them from spreading. Colder conditions seem to stop their spread as they become lethargic & even killed in low temperatures.

Epidemiology

When a worm takes over a host, it will either force them to travel to the nearest queen to increase the numbers or travel to a new area to develop into a new queen. There it will lay eggs in it's waste that gets into the water system of the area. Some will develop into adult worms to defend the eggs & larvae, and can still violently enter the bodies of victims if there is too much adults present. 
The eggs & larvae are waterborne and either drunk without the water being sterilised, or through contaminated food due to improper food processing or cleaning habits. The queen will see to the mass production of these eggs, though the standard adult worms can produce smaller clumps of them by themselves, especially if no queen is present as her phermones will override their production.

History

Millions of years ago experiments were carried out by an unnamed species on breeding parasitic worms in the swamps of Pangea. 
Exactly who this species was nobody is sure though some ancient artifacts do surface once in a while, and speak of an ancestor species of most of the sentient races of the world. A twisted group of such creatures had a preference for the warm swampy regions of Pangea and was at war with other elements of their people. Looking for a way to infiltrate & damage their enemy assets they struck upon an idea. Noticing that parasitic worms could be found within certain individuals they thought that by breeding a worm that could reside in their enemies bodies weakening them from within. They tried breeding different strains, each with a different base worm that attacked their enemies in different ways.
Most proved useless and were discarded or stored for possible further study down the line. That is until they encountered the Mindflayers when said creatures appeared in some of the underground lairs of some of the species. Seeing how the Mindflayers starting of as a tadpole-like creature that eventually took over the crainial mass of their victims, the species knew what to do.
They started to breed worms that burrowed into the tissue of their victims and made their way to the brain & brainstem of the host. From there the host could act as a puppet for a hive mind of the worms and the queen when she emerged. The line of thought was that the species could use magic or psionic powers taught to them by the Mindflayers to dominate the queen, and get her to control the other worms in each hive. This could be used to sabotage, assassinate key individuals, and misdirect them where possible.
Unfortunately, it turned out that they had used some of the Mindflayer young, who took great offence at this and proceeded to destroy the worms, the species and their twisted empire.
Now only the worms remain and are generally buried away awaiting the rare few treasure hunters & adventurers that enter the old ruins of this empire for profit. Some times a bit of the lore concerning the creation of these worms are found alongside the parasites. Some in the know actually search for the parasites looking for a way to control others especially the lower levels of society.
So far incidents involving the worms are extremely rare at present but the risk these falling into the wrong hands is always present.

Cultural Reception

Hate d& feared since their inception, when the brain worms are encountered the local communities & any authority groups will look to exterminate them in any way possible. The whole process of the worms life cysle is repellant to nearly all known species, though the creatures known as Mindflayers or Illithids seem to show an affinity for the worms.

Type

Parasitic

Origin

Engineered

Cycle

Chronic, Acquired & Congenital

Rarity

Extremely Rare