This is the submissions for plagues and other mass effecting diseases. Most will simply be scroll additions, while others attached to settings or other submissions will be added as a codex post.
Additional Ideas (18)
God's Death is a plague that is carried in the blood of birds and the fleas that live off the birds. Normally there is no contact between these fleas and human beings, but as a bird host die, these fleas are forced to seek alternatives - including humans!
The infection then spreads to everyone who had any contact with the diseased. Those infected feel themselves penetrated by a pain throughout their whole bodies and, so to say, undermined. Then there developes on the thighs or upper arms a boil about the size of a lentil. This infects the whole body, and penetrates it so that the patient violently vomites blood. This vomiting of blood continues without intermission for three days, there being no means of healing it, and then the patient expires.
Not only all those who has speech with them dies, but also those who has touched or used any of their things.
Three days is the longest an infected can possibly survive.
It is named Gods death since some religions belive the plague to be a punishment from God/Gods.
Spotted Plague is a highly communicable disease the occurs in the vicinity of the Deepwood, and other deciduous regions of the Midlands. It is spread by ticks, especially those born by deer and other prey animals. The victim begins to exhibit odd signs for two or three days, headaches, bouts of dizzyness, and mild nausea. At this point, administration of curative magics and alchemical healing and cure potions will eliminate the disease. The victim is not yet spreading the disease.
After three to five days of being infected by the tick, the victim will begin to break out in small skin lesions. These pustules will be painful and swollen, often itching as well. The pus is highly infectious, and will transmit plague to those who come in contact with it. Vomiting, intense body pain, and fever can only be reduced by the strongest healing magics, and cannot be counter acted by commonly available curative potions. A special curative potion designed to specifically counter this plague could work, but must be made for the most current strain of the illness.
After 7 days, the victim will either enter the final stage of the disease, or they will begin to get better. The final stage is marked by bloody discharge, hallucination and muscle spasms, ending in death. The corpses of the victims are virulent for two to three days after death.
In the Deepwood, an outbreak of the plague can decimate small communities, but as the plague has a slower period of incubation, and limited transmission, it can be contained, and the Midlands has only had two epidemics of Spotted Fever.
In RY 1135, 22,000 people in the area of Lynwall and Jericho perished as result of the plague. Another 15,000 wore the small scars of spotted plague for the rest of their lives. Only the action of the Imperial Wizardry and the containment by the Queen's Guard prevented the plague from spreading further than it did.
In RY 1207, an unknown number of people died as Spotted Fever broke out in six seperate locations, including two areas that are known to be outside of the general area of the disease. Zhalan, in Angbad suffered losses in excess of 50% of the population, and the independent province of Caldwell, long isolated from the Midlands lost 4 out of 5 of the populace. These were the worst hit as neither area had any experience with the Spotted Plaugue. The Deepwood province, most often effected by the illness suffered minimal losses, and is was later discovered that the Deepwood outbreak was secondary, caused by cityfolk escaping to the countryside. The instigator of the outbreak was never discovered.
This plague is actually a parasite. It effects the brain, central nervous system, the heart, and the lungs. The parasite seldom kills its host, but infection leads to chronic tiredness and difficulty thinking clearly. People can live and function with an infection nearly forever. Those effected breath out "spores". People who breath in near an effected person, breath in the spores which hatch into the parasites. Since you can live with the parasite for quite a long time, the infection rate for a population is nearly 100%.
Upon death, the parasite begins to "assist" the host. Some time after death, the parasites begin to restart the heart and work around various bits of damage. The target is able to walk about and is quite immune to most pain. The host has suffered a bit of brain damage by this point, so they are not high functioning. In fact, the immunity to pain requires the host to be seriously traumatized (head removal and serious bloodloss) or burned (parasites do not handle high heat well) to stop them. The hosts begin to search for living beings to "bite", so some of their parasites can jump ship. Those who are not able to "jump ship", motivate the host to eat the brains and other nerves of people (so they can have more fuel).
In an effected population an outbreak that begins upon a non cremated death can explode into a massive problem as "Walkers" begin to shamble about in search of new hosts or food sources.
Note: Most walkers will "hide" by day, to avoid overheating in the sun.
Imagine if a cat investigated a dead/ infected walker. There could be transmission of the disease to another species. And the disease may respond differently.
The fun part is, they may or may not be dead when the parasites take over. In fact, the slightly more intelligent parasites (since they have been feasting upon Human brain matter) might make for more intelligent cats. Cats, having a lower body temperature than humans, might be a better host. They a now smarter cats that have a symbiotic relationship with the parasites.
And it could explain the 9 lives of the cats. The parasites might be able to manipulate the smaller and simplier body of the cats. They might even be able to effect more repairs than just a restart.
Originally Posted by New Scientist
Forget needy teenagers the pros of manipulative behaviour are parasitoid wasps.
Having partially developed inside caterpillars, the larvae of the wasps manipulate their hosts into watching over them as a mother or bodyguard might.
A team that has done extensive field studies with infected caterpillars say they have the first conclusive proof that the manipulative behaviour of some parasitoids increases their chance of survival.
The parasitoid wasp Glyptapanteles lays its eggs, about 80 at a time, in young geometrid caterpillars. The eggs hatch and the larvae feed on the caterpillar's body fluids. When they are fully developed, they eat through the caterpillar's skin, attach themselves to a nearby branch or leaf and wrap themselves up in a cocoon.
At this point, something remarkable and slightly eerie happens.
The caterpillar, still alive, behaves as though controlled by the cocooned larvae. Instead of going about its usual daily business, it stands arched over the cocoons without moving away or feeding.
The caterpillar now effectively a zombie stays alive until the adult wasps hatch.
"We don't know exactly what kills the caterpillars, but it is fascinating that the moment of death seems to be tuned to the duration of the wasp's pupal stage," says Arne Janssen of the University of Amsterdam.
Janssen and colleagues at the Brazilian Federal University of Viçosa noticed that when they moved a paintbrush towards parasitised caterpillars, the insects would thrash about, apparently in an attempt to protect the cocoons.
It wasn't the first time that parasites have been seen to manipulate the behaviour of their hosts. One parasite, for instance, infects an ant and appears to "convince" it to climb to the tops of blades of grass where it is more likely to be eaten by grazing sheep which the parasite needs to get into in order to complete its life cycle.
But no-one had yet been able to show that the manipulation was not random and did indeed serve the purpose of the parasite. It could be that, rather than changing their behaviour, the parasites simply choose hosts that have abnormal behaviour.
To test the manipulation hypothesis, Janssen's team allowed wasps to infect caterpillars in a laboratory setting. Once the larvae emerged and formed their cocoons, the researchers separated half the cocoons and the caterpillars. The separated cocoons were attached to a leaf next to an unparasitised caterpillar, which was prevented from moving away by a ring of insect glue around the stem.
When they added a stinkbug, a voracious predator of wasp cocoons, the team found that 17 of the 19 parasitised caterpillars thrashed their heads around in the direction of the bug. More than half the time, this knocked the bug off the branch or made it retreat. Unparasitised caterpillars barely noticed the bug, even when it climbed on top of them.
To see if the behaviour affected the survival of wasp cocoons in the wild, the researchers placed over 400 parasitised caterpillars in guava fruit trees one day before the larvae were due to break through their skin.
Once the larvae had cocooned themselves on the nearby branches, the researchers removed half of their bodyguard caterpillars and watched what happened. The survival rate of "guarded" cocoons was twice as high as that of unguarded cocoons.
Wasps 1 caterpillars 0
"The study is absolutely fascinating," says Frédéric Thomas of the Institute for Research and Development in France. "It is the first documented case of manipulative parasites making the host behave as a true bodyguard to protect the parasite. And the experiments show the behavioural change is beneficial only for the wasp."
Although Janssen and his colleagues do not know how the parasites make the caterpillars change their behaviour, they think that a few larvae in each brood may sacrifice themselves to help their brothers and sisters.
"If we dissect the caterpillars, we find one or two parasitoid larvae have stayed behind, even after the rest of the brood has emerged and formed cocoons," says Janssen.
It could be that the larvae that remain in the host control its behaviour in order to make it protect the rest of the brood.
Journal reference: PLoS ONE, DOI: 10.1371/journal.pone.0002276
Only hours after infection the infected starts to have delirium, hallucination and sharp muscular cramps, quickly followed by yellow and black vomit. The excreta is a black pulp of blood with lumps in it. After three hours the body is covered with obscene black boils, terrible red rushes and ghastly blue pallor.
At the fourth hour the disease causes lumps of flesh to fall of, revealing a milky green pus. The pain of this desease is so great that the infected is constantly awake. If they pass out because of the pain they wake up only minutes later by an even greater pain. At the sixth hour the infected are either mad or dead. Nobody survives longer that 8hours. The bacteria keeps eating the body days after death. The plague remains contagious as long as the skeleton is covered in flesh. If undisturbed the plague can eat an entire body in less than three days.
The carriers of this plague is actually an extremely rare flower which blooms at full moon only. It grows in rough mountain terrains. But when it blooms this flower releases flower dust which contains the bacteria of the Aninchorra plague. The chanses are slim that any unfortunates should be nearby at the time. But if someone is infected and travels to a city within two hours,
this Flower born disease will prove to be one of the most virulent killers.
Orcs are known for their love of war, but not for caring for their wounds. This is normally fine, as their blood contains numerous anti-bacterial agents to protect them from infection. However, these same agents are what cause Orcrot.
Orcrot is a brownish mold-like fungus that lives off of blood. Orcrot starts when the first spore touches the wound. That spore is fertilized by the agents in the orc's blood, and soon the wound begins to grow a large brown patch. This patch emits hundreds of spores, making nearby orcs particularly susceptible. Also, although the spores can only grow on orcs, if the blood of another species touches the fungus, that creature can also become afflicted.
A single patch of orcrot is not fatal, but additional patches will rapidly drain the host of its strength. In game terms, a creature of average health should be drained in about 20 weeks, minus 1 week per additional patch.
Finally, restoration. Orcrot needs lots of blood to survive, so if a patch is on an appendage, merely tying a rope or tourniquet around the appendage to give the victim "Pins and Needles" (i.e. put the limb "to sleep") will kill the parasite. On the body or head, however, it must burned off. This is relatively easy for a talented healer, but can be dangerous to an untrained one.
The Burning Death is a plague which affects almost every race, primarily elves. Sages speculate thet this is due to the Elves' having so much of the "Fires of Life."
The Burning Death is caused by bacteria which inhabit the blood stream, so blood is how the disease is transmitted. Any open wound which touches infected blood has an 85% chance of recieving the disease.
The symptoms of the Burning Death are few, but they are deadly. The disease causes the person's body temperature (normally 37 degrees Celsius) to rise by two degrees every day. This is initially not so bad, but eventually causes the victim's skin to burn from the inside, which is, of course, excrutiatingly painful. Eventually, after slightly over a month, the victim's blood begins to boil, which rapidly kills the afflicted.
As the cause of Burning Death is a bacteria, medicines have been made to deal with this plague, but is mutates frequently, thus new medicines are always needed. Also, the extreme heat will kill the bacteria as well, so the corpse of a person who dies from Burning Death is not contagious. Also, if, somehow, the afflicted can be given protection from the heat, the bacteria will die before the death of the victim.
This horrific disease cut a bloody swath through Media, Aradash, and Carmania during the period after the Casterian War, when the armies of those nations, exhausted from the vicious fighting against the Casterians on the very border of what is contemporarily termed Ageratos, began to return home. The plague is commonly believed to have been created by King Harn-Dan of the Casterians, a sorceror of no small note; the natural philosophers of the Parsic Empire maintain a theory that it was born from an infusion of Underworld elements in the natural elements of the battlefields, causing the soldiers to breath in the air of death and creating this necrotism.
It's name comes from Lord Aars of Taastrin, one of the major elector-lords of Aradash, the first noble victim of the plague (as is the Aradashi tradition, peasant losses to the plague are not acknowledged as having occured- their society is highly elitist). In Aradash, the plague was not wide-spread (or at least was not reported as such; the counts may not include many of the peasants who died from it), while the population of Media was nearly halved. By the time the sickness reached Carmania, the worshippers of Amalias had recieved many horrific tales of it's depredations in Media and many of the larger cities were prepared, with holy defenses and rituals performed by Amalian Magi, though much of the southern countryside was quite significantly struck.
Surprisingly, it seems that the Plague was ended there. The Median and Carmanian policies of sealing ports during the period of illness (one generally attributed to the little known Median logistical genius Uistheca of Paliar, tragically slain by the plague which helped to stop) stopped the disease from spreading north into the ports of Parakonia, Arachosia, and Tsartis; the sparsely-populated Carmanian-Mysian border stopped almost all transmission westward; and the Gedrosian Desert sealed off the affected areas from the south, though there was a small amount of mortality in Parsis, especially in the capitol, Suza, where a Median trading caravan, unknowingly infected, spread the disease.
Little is known of the symptoms of the Plague of Lord Aars- that which can be reconstructed from the texts of Magi and doctors of the time is vague, and makes frequent references to such strange ailments as "worms of the innards", "paste bones" and "parchment of the flesh". It seems that the sickness spread from within the body and caused it slowly to disintegrate until the flesh and skin itself sloughed off the body, leaving only pulpy masses of organs and soft, spongy bones.
There is only one known cure for the Plague of Lord Aars, and it is an extremely expensive and uncertain one- the affected must be swathed in honey and breath the fumes of a fire made from latar-leaf and goldroot while a Magus speaks prayers and makes invocations.
Some 50 years after the notorious Black Plague, the lands of Icathia had an even more deadly visitor.
The White Plague was highly infective, it spread through almost the whole population. Luckily, only about 10-15% of people were killed by the plague itself. Further victims came later due to starvation (as nigh to anyone had at least mild symptoms, and many serious symptoms). The White Plague has put not only a sharp end to economical growth, but also to war preparations of several baronies, so it actually saved lives... a few maybe. The Plague has mostly hit the Human race, the other races had only minor losses.
The White Plague can have a slow offset, but rare deaths within one week from the first symptoms have been observed. The victim looses partly or completely bodily pigmentation, leaving the skin very sensitive to the sun. The less lucky (mostly those having a specific blood group, but that is not known) found their skin slowly rotting, even decomposing and dieing in horrible pains. The victims, while unable to move in the end, can clearly think and perceive what happens to them.
The healing process was significantly aided by herbs and magic, but no certain cure was found.
The Sun Disease
While much of the population are immune to the original White Plague, it still lingers on. This weaker variant is transmitted trough blood and sexual intercourse, the victim slowly looses pigmentation and it usually takes a decade or two until the secondary effects become terminal. Due to its slow onset it takes the role of early AIDS from our world (the affected people and minorities hide it as able). It is easy to mask it in early stages.
There is a hope the virus will mutate some day to be safe for its host.
The URU Plague is like the flu, it comes in new varieties every few years. Every decade or three it becomes seriously dangerous. No one is sure on the exact origin of the URU plague, but it is named after one of the Great Dark Lords that first took advantage of it and its victims.
The plague will sweep across a population. Everyone will catch it. People show the symptoms of being jaundiced and their skin will settle between jaundiced yellow and a putrid green tone. For most it is an terrible cold with fever that lasts 7 days. The weak and the young will often die from it. However, for a percentage of people it is more... much more.
For those that are considered "tainted" (after the fact), they are transformed. In under three days, they become one of the "tainted races". Their body begins to roll and shift, almost visibly before the eyes. Their faces will strech and be distorted... especially as new fangs grow in. Most who are tainted manage to escape as most of the people around them are too weak to stop them. These victims form small tribes that eventually merge with other ones, making for deadly tainted nations.
Note: Elven victims become High Orcs, the most deadly of the tainted races. Low Elves (Forest and Desert), as well as Humans become Orcs mostly, but Goblins and other foul critters are possible. It all depends on the "strain" that comes through that year. Dwarves become Hobgoblins, their most hated foe. Insert the tainted races of your choice and setting. Transformed people can function as a "born" member of the Tainted Race with no signs that they were ever "normal".
The Fire Blossom Plague is a terrible disease which has ravaged the lands of the Southern Sea for centuries. Periodically, this contagion will blaze through the southern lands, usually from west to east (the common conjecture of it's provenance is that it comes from the Great Western Wilderness). The disease thrives only in the hot, wet climes of the Southern Sea; lands such as Bithynia and southern Izada are often decimated during the Fire Blossom's cycle.
The first signs of the disease are purplish-red blotches along the ribs and pectoral region, which deepen to blue-black, bruise-like leathery spots after a few days. When the disease is first contracted, the victim experiences a short period of fever, after which there are no symptoms other than the rash of spots.
The second stage of the disease generally begins during the hottest, wettest months of the summer. The black blotches widen and rise into fleshy tumours which itch abominably. When scratched, however, they crack and flake away, becoming the eponymous "fire blossoms", staggeringly-painful wounds which have the appearance of daisy-shaped crimson blisters, and which engender further blotches (the seeds of even more fire blossoms) around them.
The third stage of the disease occurs near the end of the long southern summer- the fire blossoms have now spread to all parts of the body. By now the victim generally cannot walk; most attempts to move result in crippling pain and profuse bleeding from the fire blossoms. The victim begins to cough up blood at this stage.
The fourth and final stage occurs after the end of the summer season. At this point, the victim is wasted and immobilized by the disease. The victim coughs up pieces of the organs. This stage lasts little longer than a month, and ends in an excruciating death.
Fire Blossom Plague is spread through the air. The coughs of the victim, as well as the broken fire blossom wounds, dispatch a bloody mist which tends to hang around the victim. Breathing in the vapors of this mist can spread the disease.
Lucheres was a famous worker of wonder in ancient times. According to the legends, the weight of his magics was so great, that he could barely lift his body. Yet he compensated by doing everything with his mind.
The Lucheres Fever is a disease that has become more and more prevolent over the recent decade. The symptoms are fever, usually quite high, and incredible weakness. For most, the fever lasts for a week, the weakness continues on for another moon or so. A few die (usually the old), but most recover. Of those that recover, many develop a lingering weakness either over their whole body or just a single limb.
For some, the fever is dangerously hot. If they survive it, and are not made a vegetable by the fever, they awaken with an expanded mind. They develop innate mind magics, and can develop some strong magickal/ thaumaturgical skills. However, there is a price for this "gift". Their body is forever weakened. More than three steps is a great exertion for them, causing fatigue and slight pain. Lifting more than a goblet or plate is really more than they can do. So the victims of the fever live forever as Lucheres did, laying about doing things with magic, slowly wasting away.
Now imagine if this was the only way to have magical gifts on the world?
aka Dragon's Curse or Silver Scales
It was once through that Dragons had become less and less magical over time. Eventually they became "people". The true root of this idea is unknown, but one can point to this childhood disease.
It strikes children, usually toddlers to tweens. Most get a mild case. It creates a few patches of crusty white "shingle" or scales upon their skin. The skin dries and thickens slightly as infested, contracting and scarring as it does. This is accompanied by a high fever, dehdyration, and lack of appetite that runs on and off for a fortnight. There is sometimes some minor scarring due to the scales.
Certain children will have higher fevers and have quite a number of patches over their body, usually on their face. If they do survive they will have notable white/ silver scales (shingles) and scars where the deep shingles eventally peel away.
A generation that has been with with Dragon's Scales, which will happen about every 8 or 16 years or so, will usually be marked with scars. At least once you have been touched by the disease, you can never get it again.
The mortality rate in the children is around 15%, but this varies (usually up) due to less ideal local conditions and care.
A variant story is that dragons, hating humans that hunted them, cursed them to become dragons. Humans not having enough magic, simplied stalled in their transition.
The Diety Phageous, the God of Plagues, never had a regular worship. Humans would flock to him in droves during a plague, but would ignore him in times of health.
Being a jelous god, he resented this. He wanted people to worship and believe. He hatched a scheme that other Gods would not oppose. Rather thant awaiting a regular time or inflicting a plague that another deity wished, he was going to unleash is own disease.
It was a horrible disease. Pox and pustules appeared over most of the body, causing pain to the point of agony in the fevered patient. After 9 days, they would burst and spread more plague. Eventually the bleeding, the infection, and the fever will bring down the inflicted.
The Plague was created to strike down "disbelievers" (those without Gods). Those who only paid lipservice to their faith, would be struck down as well; "those of little faith" (10 to 15%), would be struck down to keep everyone else in line. They would believe or they would die.
The Gods did not like this new plague. However it was in Phageous's domain and technically supported those that believe in The Gods. They would quibble, but be unable to stop him.
Civilization came screaching to a halt due to the loss of people. It took nearly two generations to really recover from the loss of skills and the chaos of succession.
The plague does linger, and those that do not "have an allignment with a God", will periodically sicken and die.
Many children, not annointed in their faith began to sicken and die as well, but the other gods intervened. Thus the children might get a mild case about about age of confirmation, "just to remind the parents" and cause them to annoint their children. If the children lose their faith as an adult, they can catch the disease again.
Note: Phageous has gotten his wish. The lingering plague has caused many a city to create Temples to the Plague God. There is minimal worship there. The priests and the family of the ill are his only worshipers. These temples are where most cities quarrentine their sick people.
It is a disease that comes from highly magical worlds. It causes people to suffer pain when magic is used on them and in more advanced stages, around them. It pretty much acted like a mix of HIV and cancer, except that it attacked a character's 'natural' ability to resist harm from magical energy fields. The logic was that evolution probably gave all the races, over time, some kind of natural resistance to magic(in some ways reflected by the amount of effect/ damage a spell does). If a person spends too much time around magic, that 'immunity' might start to weaken (like your body's defenses would if you spent too much time around radiation).
The disease strips away that natural immunity. Thus minor attack spells might go from 1d4 to 1d4+1d6 as the body was wracked with pain from a magical energy it no longer knew how to handle. Picture an albino suddenly exposed to the sun in a high-UV area and you get the idea.
This would get worse and worse to the point that even healing spells would cause the character pain.
The cure might be available, but it will be time consuming, expensive, and there will be a chance of relapse.
While this disease could of evolved naturally, from a microorganism that absorbs magical energy (thus it is immune to the effects of the spell, even if the host is not). If there is enough magic and magical healing (and magic items) in the world, it will cause the diseases to adapt.
I do like the idea that this is a curse from a long-dead God that was being held behind some strong magic. The PCs unwittingly (even if you give them the clues saying 'DO NOT OPEN') open. Thus unleashing an ancient curse.
It is a hideous and devastating airborn disease that causes "sharp pains, and sudden dizziness, and then profuse bleeding at the pores, with dissolution." Its victims, covered with blood, die within an hour of contracting the disease.
The disease has a high transmition rate. No one seems to be able to escape the disease.
"The scarlet stains upon the body and especially upon the face... shut out its victims from the aid and from the sympathy of his fellow men." You see the marks of the red death and you simply run hoping to save yourself.
Edgar Allan Poe is the master of morbidity. His tale, The Masque of the Red Death, the prince holes himself up in his castle with a thousand of his friends to dodge the plague, but it infects everybody anyway, proving that nobody can escape death -- not even the wealthy.
When the founts of dark magic flared one midwinter eve, all prepared for the worst, yet no demon appeared, no legions of the walking dead. What was thought a false warning manifested in full only later.
Arcane writing would appear on unfortunate individuals, unintellegible to all except those well-versed in the dark arts, the same sign repeated several times on the unfortunate person's body. The afflicted would see it in their sleep, draw it unwittingly when their mind drifted or during hours of rest; it would sneak into their handwriting, into their art, into the patters they stirred into soup, repeated over and over again.
Soon, a cloud of dark energy would follow them, to manifest as a malevolent, uncontrolled spell - a dire curse, destructive manifestation, unholy summoning...
The Marked know that the harmful magic will manifest over and over again, sparing them but no-one else. Some of the victims of these involuntary castings develop dark runes of their own. Confronted with this, many of the afflicted seek solitude or death.
Some unsavoury wizards have learned to leech the accumulating dark energy from the Marked, to fuel their fell sorcery. The sufferers are relieved that their curse seems ameliorated while the black mage is present, until they learn that the energy they generate causes harm anyway, often on a greater scale.
I can see this happening to "unbelievers" or those who give lip-service to a deity, the deity in question (assuming one that can be generally classified as 'good') protecting the true worshipers and letting the others rot, perhaps as a subtle prod into actual belief.
I can also see it having different "strains," i.e. different sets of dark runes based on what 'infection' you originally got, each of which has a different end result. "Oh, that one isn't one to worry about. He just gives everyone around him the willies. We need to kill that guy though, his runes raise the dead!" A particularly crafty dark wizard might try something like this, perhaps with the undead outlook, or even just a generic buildup of dark energy within his kingdom, to make his dark arts easier to practice.
It is not an infectious disease, but it is a plague upon the world.
For it spawns villains. And not your garden variety villains, but epic villains, master villains of the most dangerous kind Evil Geniuses.
Proof that your fantasy/ horror zombie is at home in science fiction - Star Wars to be specific
Plague was a disease designed by Sith Lord Karness Muur, which, when combined with the Muur Talisman could turn others into mindless thralls he could command. After under unknown circumstances the Talisman ended up in the Undercity of Taris, where the Rakghoul Plague raged in the Undercity for many centuries.
All non-Force-sensitives who encountered direct contact with the Talisman were almost immediately transformed into rakghouls. These monsters further spread the plague amongst the Outcaststhe inhabitants of the Undercity of Taris. Individuals infected with the disease would later transform into rakghouls themselves.
After (violent) contact with a rakghoul, infection with the disease was a rapid and painful experience. The victim was transformed into a rakghoul within 6 to 48 hours. Bodies would become twisted, skin pigmentation would drain and the victim would turn attain a whitened corpse-like state.
In 3,963 BBY the excavation team of Mandalorian Neo-Crusaders, lead by Pulsipher, located the Talisman in the Undercity and took it to Jebble, where, unfortunately, the Rakghoul Plague once again took hold. But since the Talisman had an owner/ user, These rakghouls were different, they could tap into their learned skills to use weapons and vehicles. A nuclear bombardment of Jebble, wiped the rakghouls from the face of the planet.
Now, when the original source of the Rakghoul Plague was removed from Taris, it was further spread only by those already transformed into rakghouls. This, however didn't make it any less dangerous. By the time of the the Jedi Civil War it was estimated that up to 60 million people of Taris had been infected.
Now we can have Zombie Planets