Diseases

From Dungeon Master's Guide, page 256; Explorer's Guide to Wildemount, pages 125 and 241; Ghosts of Saltmarsh, page 234.

A plague ravages the kingdom, setting the adventurers on a quest to find a cure. An adventurer emerges from an ancient tomb, unopened for centuries, and soon finds herself suffering from a wasting illness. A warlock offends some dark power and contracts a strange affliction that spreads whenever he casts spells.

A simple outbreak might amount to little more than a small drain on party resources, curable by a casting of Lesser Restoration. A more complicated outbreak can form the basis of one or more adventures as characters search for a cure, stop the spread of the disease, and deal with the consequences.

A disease that does more than infect a few party members is primarily a plot device. The rules help describe the effects of the disease and how it can be cured, but the specifics of how a disease works aren't bound by a common set of rules. Diseases can affect any creature, and a given illness might or might not pass from one race or kind of creature to another. A plague might affect only constructs or undead, or sweep through a halfling neighborhood but leave other races untouched. What matters is the story you want to tell.

Sample Diseases
The diseases here illustrate the variety of ways disease can work in the game. Feel free to alter the saving throw DCs, incubation times, symptoms, and other characteristics of these diseases to suit your campaign.

Cackle Fever
This disease targets humanoids, although gnomes are strangely immune. While in the grips of this disease, victims frequently succumb to fits of mad laughter, giving the disease its common name and its morbid nickname: "the shrieks."

Symptoms manifest 1d4 hours after infection and include fever and disorientation. The infected creature gains one level of exhaustion that can't be removed until the disease is cured.

Any event that causes the infected creature great stress — including entering combat, taking damage, experiencing fear, or having a nightmare-forces the creature to make a DC 13 Constitution saving throw.

On a failed save, the creature takes 5 (1d10) psychic damage and becomes incapacitated with mad laughter for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the mad laughter and the incapacitated condition on a success. Any humanoid creature that starts its turn within 10 feet of an infected creature in the throes of mad laughter must succeed on a DC 10 Constitution saving throw or also become infected with the disease. Once a creature succeeds on this save, it is immune to the mad laughter of that particular infected creature for 24 hours.

At the end of each long rest, an infected creature can make a DC 13 Constitution saving throw. On a successful save, the DC for this save and for the save to avoid an attack of mad laughter drops by 1d6. When the saving throw DC drops to 0, the creature recovers from the disease. A creature that fails three of these saving throws gains a randomly determined form of indefinite madness.

Sewer Plague
Sewer plague is a generic term for a broad category of illnesses that incubate in sewers, refuse heaps, and stagnant swamps, and which are sometimes transmitted by creatures that dwell in those areas, such as rats and otyughs.

When a humanoid creature is bitten by a creature that carries the disease, or when it comes into contact with filth or offal contaminated by the disease, the creature must succeed on a DC 11 Constitution saving throw or become infected.

It takes 1d4 days for sewer plague's symptoms to manifest in an infected creature. Symptoms include fatigue and cramps. The infected creature suffers one level of exhaustion, and it regains only half the normal number of hit points from spending hit dice and no hit points from finishing a long rest.

At the end of each long rest, an infected creature must make a DC 11 Constitution saving throw. On a failed save, the character gains one level of exhaustion.

On a successful save, the character's exhaustion level decreases by one level. If a successful saving throw reduces the infected creature's level of exhaustion below 1, the creature recovers from the disease.

Sight Rot
This painful infection causes bleeding from the eyes and eventually blinds the victim.

A beast or humanoid that drinks water tainted by sight rot must succeed on a DC 15 Constitution saving throw or become infected. One day after infection, the creature's vision starts to become blurry. The creature takes a -1 penalty to attack rolls and ability checks that rely on sight. At the end of each long rest after the symptoms appear, the penalty worsens by 1. When it reaches -5, the victim is blinded until its sight is restored by magic such as Lesser Restoration or Heal.

Sight rot can be cured using a rare flower called Eyebright, which grows in some swamps. Given an hour, a character who has proficiency with an herbalism kit can turn the flower into one dose of ointment. Applied to the eyes before a long rest, one dose of it prevents the disease from worsening after that rest. After three doses, the ointment cures the disease entirely.

Frigid Woe
(Explorer's Guide to Wildemount, page 125)

Frigid woe is a special disease developed by Aeor's mages that cannot be cured by conventional treatment or magic. The only way a creature infected with the disease can be cured is by finding and drinking the manufactured antidote, a milky liquid stored in gold vials found in Eiselcross' ruins. This disease was created to slow down the forces of the gods and get around the healing power of their clerics and angels.

The disease is transmitted by breathing in blue spores that Aeor's mages created long ago. When a creature comes into contact with these spores, it must succeed on a DC 11 Constitution saving throw or become infected with frigid woe. It takes 1d4 days for the symptoms to manifest in an infected creature. The infected creature's speed is reduced by 5 feet as long as it remains infected. Every 10 days after symptoms appear, an infected creature must succeed on a DC 11 Constitution saving throw, or its speed is reduced by another 5 feet. If a creature's speed is reduced to 0 as a result of this disease, the creature dies and its body turns into a statue made of ice.

The creature can drink the antidote as an action, ending all symptoms and effects of the disease instantly.

Vial of Frigid Woe
(Explorer's Guide to Wildemount, page 241)

As an action, a creature can throw a vial of frigid woe up to 20 feet, shattering it on impact and releasing its contents as a cloud of spores. Each creature within 5 feet of the vial when it shatters must succeed on a DC 11 Constitution saving throw or contract frigid woe.

If a character contracts frigid woe, track the number of days that have passed so you can inform the player when their character's symptoms appear and when they need to make Constitution saving throws.

Bluerot
(Ghosts of Saltmarsh, page 234)

This disease target humanoids. While afflicted with bluerot, a victim grows grotesque blue boils on their face and back. This disease is carried by undead (including the drowned ones in Tammeraut's Fate), and victims most often acquire it through wounds caused by infected creatures.

The disease's boils manifest in 1d4 hours, causing the victim's Constitution and Charisma scores to decrease by 1d4 each, to a minimum of 3. This is quickly followed by a fever and tingling in the extremities. An infected creature is vulnerable to radiant damage and gains the ability to breathe underwater.

At the end of each long rest, an infected creature makes a DC 12 Constitution saving throw. On a success, the victim regains 1 point of Constitution and 1 point of Charisma lost to the disease. If the infected creature regains all the points lost to the disease, it is cured. Other effects that raise the victim's ability scores do not cure the disease. On a failed saving throw, the victim takes 18 (4d8) necrotic damage as the boils burst and spread. A creature reduced to 0 hit points by this damage cannot regain hit points until the disease is cured, though it can be stabilized as normal.