Diseases are terrifying enemies, hidden from sight and senses. Many of those who become afflicted with a disease do not even know what has entered their bodies. Despite the fact that diseases care little for their victims and claim anyone who comes near, those of evil heart are still willing to use them for their own, vile purposes. As a weapon, disease has many advantages. It doesn't require its wielder to be nearby - one can simply enter a town or hamlet, drop some diseased matter in the well, and disappear again.

Diseases, while a great plot device, should not be thrown at the characters at random or without good reason, but players should not tramp all over the world thinking themselves immune to catching a disease. Adventurers wading through thigh-deep water in a sewer should expect to run at least a chance of contracting some kind of disease; those travelling through a desert in the middle of summer probably should not. The trick here is to seek a balance between reasonable danger and providing a new challenge for the players, and simply inconveniencing them and possibly killing one or more of the PCs with something they cannot combat.

Contracting Diseases

Each game month, make a check for each character to see if (s)he catches a disease. This assumes normal activities – immediate checks should be made if, for example, a character with open wounds falls into filthy sewer water, or for those present when a crypt is cracked open for the first time in centuries. If the percentile roll indicates the character is diseased, choose an appropriate one from the list, apply a Fort save as normal to resist its effects, and go from there.

Base Chance of Catching a Disease: 2%

Condition Modifier
Currently infected with disease or parasites +2%
Character is in a marsh, swamp, or jungle, or a hot/moist climate +2%
Crowded conditions conducive to the spread of disease1 +5%
Current location has poor sanitation +5%
Character is exposed to possible source of disease (see above)2 +10%
Character is in an area of a disease outbreak Var.3
Cool weather/climate -3%
Cold weather (winter) -5%

1 Crowded city, on a ship, in a camp or a city during a siege, etc.

2 This does not stack with being in the area of an outbreak (see below) – it is applied to singular cases of exposure to a possible disease.

3 There are different levels of outbreaks, listed below, which are categorized by numbers of infected. The reasoning here is that the greater the number of people infected, the more likely it is that the character will encounter a carrier and have a chance to catch the disease himself.

Level Modifier
Outbreak (up to 100 people) +1%
Scourge (100-1,000 people) +3%
Plague (1,000-10,000 people) +10%
Epidemic (10,000+ people) +20%
Pandemic (100,000+ people) +50%

Plagues and Epidemics

Due to the large number of variables inherent with any disease (incubation time, contagion time – how long a person is contagious – communicability, etc.), it would be too difficult to come up with a hard and fast system for charting the spread of a given disease. Instead, we'll provide a set of guidelines for DMs to create outbreaks of diseases in their games.

Diseases with short incubation times and high fatality rates tend to burn themselves out quickly and are easiest to contain. Those with longer incubation times and low to middling fatality rates (influenza, e.g.) run the best chances of being spread, assuming they are indeed contagious. Obviously, environmental conditions will aid or prevent the spread – diseases are more prevalent in the summer months, during sieges, in crowded cities, and anyplace with poor sanitation (see Contracting Diseases, above).

People infected with disease can, of course, pass on their illness to those around them if it's contagious. There is no hard and fast rule for this, as it depends on many factors, the disease's vector being the most important.

Inhaled diseases can spread most easily. Anyone within 10 feet of a person infected with an Inhaled disease (cackle fever, e.g.) must roll a Fort save (using the disease's save DC, with a +4 bonus) to avoid being infected when the carrier coughs, sneezes, or otherwise does something to spread the disease.

Contact diseases are nearly as easy to spread as inhaled ones – simple unprotected contact with an infected person, or something the person has touched (including his clothes or bed sheets), runs the risk of contagion – the person must make a Fort save with a +2 bonus each time this occurs, or contract the disease himself. Viruses and bacteria vary on how long they can last on a surface, but a good rule of thumb is 1d4 hours per 4 points of the save DC over 10 – that is, a disease with a save DC of 18 would last for 2d4 hours before becoming nonviable. Casting remove disease on an object will automatically cleanse it, as will simple application of soap and hot water, alcohol, or other substances that clean and/or sterilize.

Ingested diseases are difficult to spread – it generally requires contact with a person's body fluids: waste, vomit, blood, etc. – but since such diseases are typically acquired from tainted food or water, all those in the same area usually partake of the same source and are thus infected anyway.

Injury diseases are perhaps the hardest to spread, as they are generally confined to the victim's bloodstream. Obviously, contact with the infected blood (direct transfer into an open wound, ingesting the blood, or having it splash into one's eyes) will automatically infect someone (Fort save, no bonus).

Characters Afflicted with Multiple Diseases

In very rare cases (usually as a result of failing his save against two or more disease-causing spells), a character may become afflicted with two or more diseases. Each one affects him equally; however, the DCs to shake off the effects of each are increased by +4 per disease. So, for example, if Herne already had filth fever from a dire rat's bite, then he contracted ghoul fever from a ghoul, the save DC for the first disease would be increased to 16, and the one for the second to 19. If Herne were unlucky enough to contract a third disease, the DCs for all three would be increased by 4 again.

Recovery, Immunity, and Vaccines

Just as someone can catch a disease in the real world, recover from it, and forever after be immune to it through the presence of antibodies, so too can it happen in a fantasy world. This rule is not recommended for use against supernatural diseases, except in very rare cases, but characters can gain immunity to normal ones. Immunity to a disease need not be permanent, either – a typical flu shot lasts for only one "season", so people must be vaccinated every year. Weak, mild, and moderate diseases have a good chance for someone to build up immunity, either permanently (chickenpox) or for a short time (influenza). They also have the largest number of mutations, since they are the most common, so gaining immunity to them can be problematic – the common cold is a good example. Severe and fatal diseases, on the other hand, have very few variations, since they are, on the whole, fairly rare and have a short lifespan. The AIDS virus, for example, lasts only hours outside of a host.

Enterprising alchemists can also engineer vaccines; many diseases in modern times have vaccines or pills to prevent people from catching them. Creating a vaccine is little different from creating a potion - in this case, the vaccine requires 1 day, +1 day per 5 points of the disease's save DC, and costs 100 gp per day. The Craft DC is equal to 15 + 1/5 the disease's save DC (in this case, having 5 or more ranks in the Heal skill grants a +2 bonus to the check).

Lasting Effects of Diseases

It is rather unrealistic to assume that a character could nearly die from a disease and not suffer some ill effects, so here is an optional rule: Anyone whose ability score is reduced to one-quarter or less of its original total (round down) as the direct result of a disease, but later recovers, is crippled in some way. For example, if the disease causes fits and tremors (Dex damage), the victim runs a chance of suffering from the occasional tremor or fit, especially in tense situations or when he is tired, incurring a penalty to Dex-related skills and abilities. Similarly, a disease like mummy rot or leprosy could cause permanent scarring and muscle and/or nerve damage.

If one or more scores are reduced to 0 and the victim later recovers, he still suffers permanent damage (ability drain) to that ability on the order of 1-2 points each (or more, at the DM's discretion, but it should never exceed 4). For example, a disease that saps its victim's Strength would leave him weaker than before. Ability points lost to disease in this manner can be restored via regeneration, lesser miracle, limited wish, or similar spell, but not heal or restoration.

Diseases and the Law

Most civilized societies have laws against people who knowingly spread diseases. The punishments vary, but here are some general guidelines.

Infecting a person with a disease that cannot spread from the infected person: Same punishment as murder (depending upon the severity of the disease. If the person overcomes the disease and is fully cured, the punishment would be the same as attempted murder).

Infecting a person with a contagious disease that can spread to others: As above, but each case counts as a separate victim.

Infecting a public water source with disease: If anyone becomes infected from the water source, the punishment is the same as mentioned above for infecting people. If no one becomes infected and the source of water is purified, the punishment will often be the same as for attempted murder. Societies that have few sources of water, such as desert dwellers, often punish the offender with death, regardless of the disease's lethality or if anyone was affected.


When a character is injured by a contaminated attack, touches an item smeared with diseased matter, or consumes disease-tainted food or drink, he must make an immediate Fortitude save. If he succeeds, the disease has no effect — his immune system fought off the infection. If he fails, he takes damage after an incubation period. After a set period (which varies by disease), he must make a successful Fortitude save to avoid repeated damage. The number of successful saves required varies by disease, as noted below.

These Fortitude saving throws can be rolled secretly so that the player doesn't know whether the disease has taken hold.

Disease Descriptions

Diseases have various symptoms and are spread through a number of vectors. The characteristics of several typical diseases are summarized on Table 1: Diseases and defined below.

Name: The disease's name and any nicknames or colloquial names.

Description: The disease's description, including where it is most prevalent and how often it appears.

Frequency: How common the disease is.

Common: The disease is well-known and widespread - typically, Common diseases are fairly weak
and have a large number of mutations. Examples: The common cold, influenza.

Uncommon: The disease is less prevalent, or localized to a certain climate or geographical area. Examples: Cholera, typhoid, yellow fever.

Rare: The disease is not very well known and usually only in a specific area or climate; rare
diseases usually have a high mortality rate and appear in isolated outbreaks that are usually
quickly isolated. Examples: Ebola, Marburg virus.

Very Rare: The disease has been nearly wiped out, or has a low incubation period and very high mortality rate. In a fantasy realm, very rare diseases are most often magical or divine in origin. Examples: Lhasa fever.

Severity: The diseases listed below are divided into various degrees of severity.

Mild: Almost anyone can get over the disease with little problem, even without any other aid. Examples: The common cold.

Moderate: The disease requires a week or so of bed rest, but victims can recover with minimal healing. Old and young victims often die from this disease without treatment. Examples: Influenza, pneumonia.

Severe: The disease is fatal more often than not, and often those who do survive are crippled or disfigured in some fashion. This class is also used for non-fatal diseases that cause permanent injury (blinding sickness, e.g.). Recovery without healing or magical aid is very rare. Examples: Tuberculosis, polio.

Fatal: 90%+ of victims who contract these diseases die, and very few of those who survive do so unscathed. These diseases often reach epidemic proportions, wiping out towns, cities, or even entire nations before they are contained. Examples: Cancer, Ebola virus, rabies.

Note that any disease can be fatal under the right circumstances, particularly if left untreated. These classifications are rough guidelines and can change according to the circumstances under which the disease is contracted.

Vector: How the disease is spread - through the air (airborne), casual or sexual contact (including contact with bodily fluids), ingested (through contaminated food and/or water), or injury (from dirty claws or bites, or infected objects).

DC: The DC required for the Con check to avoid or throw off the effects of the disease. The initial save to determine infection should be made secretly by the DM, so the player doesn't know that whether the character has been infected or not.

The save DC is based on the disease's severity. Also, diseases require a certain number of successful checks to recover. These checks need not be consecutive, but each success counts toward the total required. The DCs given below are rough guidelines for the DM for creating new diseases.

Severity DC Checks
Mild 10 2
Moderate 14 3
Severe 18 4
Fatal 22 4

Generally speaking, a save should be made a) when the character is first exposed, and b) at each interval, as stated in the disease's entry. If the second save fails, the victim either remains sick or advances to the next stage of the disease, as applicable.

For example, the first stage of blinding sickness lasts for 1d4 days; the victim would make his second save 24 hours after first contracting the disease, and every 24 hours thereafter (if the first stage lasts longer than 1 day). He would make a third save at the end of the time determined for that stage's duration to see if he becomes sicker.

Incubation Period: The period of time between infection and first manifestation of symptoms.

Effects: A description of the symptoms, if any, and how long they last. This entry also covers all the stages. The first stage lasts until the victim fails a second Con check, unless otherwise stated. The second and third stages' durations are listed in the disease description.

Victims regain one ability point per day of complete rest, so someone who takes small amounts of damage and makes his Con checks could easily ride out a disease with no ill effects. A successful Con check indicates that the victim takes no damage for that time increment (if applicable).

Several diseases listed in this book cause delirium, coma, and death, which often occur regardless of the victim's stat scores (see Ability Damage.

Cures: Unless otherwise noted, all diseases can be cured with a cure disease spell or a heal, limited wish, or other similar magics. This entry also covers plants, unguents, teas, etc. that can mitigate the disease's effects or cure it outright.

Special: Any special effects, like the victim rising as a zombie if he dies, the body is still infectious after death, etc. This also covers special notes, like races that are immune.

Raising or resurrecting someone who died from a disease is not a good idea, because the virus or bacteria that caused the disease in the first place will most likely still be present in the blood or flesh. If the body is still mostly intact, the victim must also make a Con check at the same DC as before or become sick again with the same disease that killed him. This does not apply for bodies that have been mostly destroyed (especially by fire) or rotted, since the pathogens are no longer present, except in special circumstances.

There are several ways to prevent the spread of disease. Foremost among them - and the most common method - is burning the bodies of the infected dead. Less common, though perhaps more thorough, is destruction of the bodies by magical means – disintegration, acid, etc.

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