Rules for disease, and a random disease generator

So your band of dirty murderhobos have been digging up ancient sealed grave sites and trudging through filthy swamps with open wounds. Those smelly rations they’re eating have been riding in their packs for a while now. The swords those goblins were wielding were coated in putrid festering gore. Adventuring is dirty, gross work.

It only makes sense that disease and infection would be a significant part of the adventuring lifestyle. Despite this most systems handle them in a way that is rather flat and boring. Either the disease does nothing until the poor fool who contracted it drops dead, or the disease just sidelines the character until it passes. That is, of course, unless there’s a 3rd level Cleric in the party. In that case they simply cast “Diseaseus Deletus” and it’s like it never happened.

When diseases come up in my games I want them to have more interactivity and unpredictability than this. This is a first stab at some rules to codify that.

Disease Rules

There are several ways that adventurers can contract diseases. Some monsters are disease carriers, triggering a save vs poison to avoid infection any time they land a melee attack. Any time a character rolls on the Death and Dismemberment table and survives, they have a 1 in 12 chance of contracting a random disease. Any time a character takes a serious injury there’s a 1 in 10 chance that they’ll contract a random disease. Each day spent in filthy conditions (marching through swamp water, crawling around in sewers, etc) results in a 1 in 20 chance of contracting a random disease, unless the party takes special measures to protect themselves.

Diseases have a Duration and a Severity. When a character contracts a disease, they begin to show symptoms in 1d6 days. While they are suffering the effects of the disease, they will have a setback die placed on all their d20 attribute tests.

The setback die begins at a d4, which is rolled along side the d20 and both dice are summed together. Each morning after the first, if the setback die is smaller than the Severity of the disease they have contracted, the character makes a CON test. On a success the setback die stays the same, on a fail it advances to the next larger die size and there’s a 1 in 20 chance they’ll pass the disease on to another PC. If the listed Severity for the particular disease is “Death”, then once the setback die reaches a d12, the character must save vs death on subsequent mornings.

Medicine can reduce the size of the setback die one step once per day. Receiving treatment from a PC with the medicine skill can reduce the setback die an additional step per day on a successful INT test. A town doctor can reduce both the Severity and the Duration by half, for a price.

Reducing the setback below d4 does not cure the disease, it merely treats (some of) the symptoms. Once the Duration has passed (counting from when symptoms show) the character can make a save vs poison to break the disease and recover. Diseases with a Duration of “Permanent” require special treatment to recover from.

In addition to the setback die, diseases may impose other effects. For instance Mummy Rot reduces the effects of all forms of healing by half. Special effects persist until the disease is healed, even if the setback is reduced below d4.

Random Disease Generator

Either roll once per column or roll once and read across.

Come up with at least one special effect based on the result. For instance “Craven Manic Tongue Fever” might cause the character to loudly make rude and obscene exclamations at inopportune times.

Duration is equal to the sum rolled for Prefix + Modifier in days, with a roll of 14+ being Permanent.

Severity is equal to the smallest die that could roll the result of Target + Affliction, with 12+ being Death. For example Stomach(2) + Infection(3) = 5 so d6 Severity.

Putting it all together, rolling 4, 8, 6, and 3 results in:

• “Apoplectic Shivering Foot Infection”
  • 12 Days Duration
  • d10 Severity
  • “Shivering”; It’s hard to carry a full pack when you have the shakes, occupies 2 inventory slots until cured.
  • “Foot Infection”; Reduces walking speed by half.