Disease and the Underworld

In the setting I write and play in, disease is very prevalent. The further you burrow into the earth, the more pockets of sickness and miasma you are likely to find. The setting follows the classical surface world > dungeon as mythic underworld > underdark/veins of the earth > writhing chaos (and also perhaps utterly alien hollow earth societies) structure, and in every instance the further you dig, the more disease there is.

There are many theories, the most common being that these pockets of disease are the vestiges of terrible wars fought by God against the monsters that ruled the earth before humans. All of the disease are communicable, debilitating, and potentially deadly - they often pose borderline existential threats to the settled societies of the surface. Because of this, healer saints are often considered the social lynchpin of any settled place past a certain size. They are an effective countermeasure, but they have their own issues (to start with, there aren't many of them and each can only heal one person once a day. There's also the issue, not generally known, that speaking with God and its angels can occasionally make you go violently insane). 

Most people associate adventurers with disease and uncleanliness, because adventurers are the ones who travel underground to fight in the dungeons. This is not entirely unwarranted; adventurers are absolutely more likely to get sick marauding beneath the earth, and then bring sickness back with them into the sunlight. Most adventurers will go out of their way to appear clean, well-kept, and physically beautiful/unblemished, and those who don't are often turned out of townships by angry and fearful citizens.

All of this means that no serious, right-minded adventurer would go anywhere near the underworld without taking along prophylactic and curative drugs in case of infection. These are difficult to manufacture but tend to work well. The alchemists and healers who develop them make a very brisk trade.

Most disease can be prevented, treated, and cured. Quarantine is effective, and if the symptoms and disease vectors are understood, then the risk can be effectively managed. The exception to this is the terrible anathema, which adventurers fear above all else, and which, uniquely, even the saints of God cannot cure. 

Anyone who has been infected with anathema will be killed with crossbows, and their remains burned with firebombs. Anathema occupies a social and cultural position similar to the devil in our world - it is one of the great adversaries to God (the other is the demons, who have no chief, or at least none that most people know about). It is very often personified in art as a gigantic, grinning, shit-and-blood-smeared corpse, sweeping hundreds of screaming humans into its vast embrace. 

RULES FOR DRUGS

Every market and town will sell drugs that inoculate you against disease, or that will act against it if you become infected. They also generally sell immune boosters and painkillers. These are all smokeable drugs, and every adult will own a pipe to imbibe them. All drugs come in standardised doses, which have listed durations. 

Everywhere will sell cheap drugs, even if it's just the local innkeeper selling across the counter. Cheap drugs have a 1 in 20 chance of not working, and are much, much cheaper than properly prepared stuff (like 10x cheaper. If an adventurer is buying cheap drugs, they are in a very bad way. No one wants to gamble with this).

Any town of a decent size will also sell properly prepared drugs. They are 100 percent effective if not ruined or tampered with. Larger towns may also occasionally sell expensive drugs, which cost twice as much, taste and smell better, and generally indicate good social standing (an expensive, decorated smoking pipe has a similar effect).

Drugs can be delicate, or robust. 

Delicate drugs will be ruined by changes in temperature. This takes effect if the holder takes fire or cold damage, or if they are exposed to environmental extremes (they get locked in a forge room, they are buried in snow). 

Both delicate and robust drugs will be ruined if they get wet. Swimming or otherwise being immersed in water will always get your drugs wet, unless you have purchased a special waterproof bag for them, or put them in an inflated bladder or something. The drugs are as follows:

Prophylactics 

This is the big important one, which adventurers will want if they are going anywhere that they know is diseased. If effective, it will prevent infection in the person who takes it. Prophylactics are delicate, and their effects last for one hour. 

Curatives 

These are what you take if you have been infected with something. They will give you a high fever (this is the drug, not the disease), but will improve your condition once step up the disease track each day until you are cured. You will be semi-conscious for the duration. Every disease has a point after which Curatives become less effective. Curatives are delicate, and a dose must be taken each day for them to continue to be effective. 

Immune Boosters 

Immune Boosters give you a small chance not to become infected in the first place. They are cheap, ubiquitous, and many people question their effectiveness. Immune boosters give you a 1 in 6 chance to ignore infection. Immune boosters are robust, and each dose lasts one day. 

Painkillers

Painkillers let you act as though you were not in pain. This has many practical effects for adventurers, but also lets you ignore the effects of infection while they are active. Painkillers are robust, and their effects last for one hour. 

Painkillers are associated with the church, who use them to ease the suffering of the dying and manufacture them in great quantities.

RULES FOR DISEASES

Disease exist in pockets of miasma beneath the earth. The diseases themselves are invisible and intangible, but the areas where they gather tend to looks and smell bad. Rot, foulness, and decay. Everything unclean, everything seething, crawling, rusting. Experienced adventurers tend to know when they are entering an infected zone (think Blight Town, The Valley of Defilement, or the Other World in Silent Hill), and this is knowledge that is quickly passed on to novices. Most diseases are airborn and can be contracted simply by breathing in the putrid air. In addition, monsters in these areas will often become infected themselves (even diseases fatal to humans rarely kills monsters outright), and will carry the diseases on their attacks. Food and water from these zones will be obviously foul and inedible. 

Dungeon rooms have a 1 in 20 chance of carrying mundane disease.

Underdark rooms have a 1 in 10 chance, and these diseased rooms have a chance of hosting the anathema.

Once you get down into Chaos, rooms have a 1 in 4 chance of being diseased. God ruined this entire strata permanently. The edifice rots and howls at the roots.

Diseases have a track that they follow, measured in days, which describes what happens at each stage, and how long it will take to progress to the next. They additionally have a randomised 'virulence' score, which is rolled for each instance of the disease encountered. Subtract this score from the listed number of days it will take to move one stage along the track - if it reduces the number to zero or bellow, the stage increases after one hour. 

Redness (Virulence 0)

Stage 1 (2 days) - Slight reddening around the lips, eyes. Body fluids carry the infection. Difficult sleeping (1 in 3 chance of not gaining the effect of rest).

Stage 2 (4 days) - Bloody welts at eyes, lips, ears, genitals, and anus. Very poor vision, as blood enters the eyes (blindness beyond 10 feet). Cough blood every five minutes or so. Body fluids still contagious. Pain slows movement by half, and all rolls are made at -2. 

Stage 3 (4 days) - Eyes are permanently ruined (character is now blind), face is a nightmare of weeping red skin. No longer contagious. Pain is incapacitating, and character can do nothing but lie still. Curatives have a 50 percent chance of failing in stage 3, and the character's vision will not return even if they are cured.

Stage 4 (1 day) - Curatives do not work in stage 4. The character loses control and will spend their final hours screaming if not drugged for the pain. TSkin is read, raw, bleeding, weeping. After a day of this they will die. 

Rot (Virulence 0-1)

Stage 1 (4 days) - Lethargy, bad breath, bloating. Breathing is contagious (anyone who sleeps in the same room, or spends more than an hour in proximity, will be infected). 

Stage 2 (6 days) - Skin turns black at the gums, armpits, groin, and belly. Small lesions form. Lose 1 max HP per day (2 per day if the Rot has a virulence of 1). No feeling at all in the extremities. They are still contagious. 

Stage 3 (6 days) - Skin is black and swollen across the entire body, the smell is overpoweringly awful. Move at half normal movement, and no longer feel any pain. They lose 2 max HP per day. They are still contagious. 

Stage 4 (2 days) - You can still crawl at a quarter normal movement. The face is not recognisable. Curatives have a 50 percent chance of not working in stage four. At the end of the two days you will die. You remain contagious throughout, as does your corpse. 

Honeycomb (Virulence 0-1)

Stage 1 (4 days) - Your pores become visible on your arms and the backs of your hands. If you look closely, you can see tiny white beads starting to form inside them. These areas become intensely itchy. Skin to skin contact is contagious. 

Stage 2 (6 days) - The pores continue to grow, until they resemble a sagging honeycomb structure spreading across the surface of your skin. The openings weep clear fluid. An intense hypnotic fever develops. The character will begin to mistake people and situations for others; at this stage the chance of this happening is 50 percent. They will also become physically stronger (+1 ST), and cycle between paranoid hyperactivity and dissociative lethargy. Even if it is cured, the affected skin will bear the scars of this disease forever. They are no longer contagious. 

Stage 3 (6 days) - Most large, exposed areas of skin are now honeycombed. There is a descent into ongoing hyperactive mania. The character will not recognise the people around them. If not restrained, they will generally become violent and paranoid. Their physical strength further increases (+1 ST). 

Stage 4 (1 day) - The head will begin to thrash around violently. This almost always breaks the neck, killing the victim, but if they are restrained the fever will burn them out after 24 hours. Curatives do not work in stage 4. 

Hypersensitivity (Virulence 0-2)

Feared by adventurers almost as much as the Anathema. 

Stage 1 (2 days) - All light becomes blinding, all sound becomes deafening, all touch becomes unbearable. All senses are 50 percent less effective, and the character loses 2 WIS. Curatives do not work. Hypersensitivity is only contagious by prolonged skin-to-skin physical contact. 

Stage 2 (2 days) - A hell of sensory overload. All the victim can do is roll into a ball and try to be as still and quiet as possible. No action is possible. Curatives do not work. They are still contagious. 

Stage 3 (2 days) - An intense, violent, and barely perceptible vibration across the entire body. The internal organs burn out and the victim dies. Curatives do not work. They are still contagious until the moment of their death. 

Anathema (Virulence 0-9) 

Stage 1 (9 days) - The person infected can no longer perceive entities, or speak any pattern languages. Angels and demons will attempt to kill them on sight. They no longer sleep, or feel any tiredness. The face takes on an instantly recognisable stretched and staring grin, which cannot be relaxed. The skin begins to discolour, like blood and faeces. They are contagious in a 20ft radius around themselves - anyone  spending ten minutes inside this radius is also infected (this includes entities, which should be impossible as they have no bodies). There is no cure. 

Stage 2 (9 days) - All muscles tighten into steel rigidity, all movement is impossible. The infected person typically stands rooted to the spot, reaching their arms towards the sky with their grinning head thrown backward. Sometimes they speak words that are impossible to understand. Angels and demons will not go near them. At the end of the ordeal they die, and the body tears and ruptures under the straining of its muscles. There is no cure.