Critical update: for a while, broke and gave random diseases upon save and reload. Fixed now. Thanks evictedSaint for reporting.

This small stand-alone mod brings all your favorite diseases to the DF world. Includes contagious disease, psychiatric illness, plagues, smallpox and cancer, as well as optionally medication for them. You can use only some of the diseases if you like. Should be compatible with any mod and may be used freely.

Installation: Copy files into raws folder, then do as ADD TO CREATURE and ADD TO MEDICINE say.

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What's included:

Disease name - prevalence - spread - nature - effect

Plagues:

Black plague - 0,03%/migrant - spreads 1x/day/diseased dwarf/touch - permanent, permanent immunity - intense pain, dizziness, nausea, swelling, oozing and small chance of permanent eye, limb or organ necrosis per month (to death). Also small chance of a deity cursing someone with this.
Bubonic plague - 0,03%/migrant - spreads 1x/day/diseased dwarf/touch - permanent, permanent immunity - swelling, oozing, fevers, vomiting blood, random necroses but fewer than in black plague. Still lethal. Also small chance of a deity cursing someone with this.
Smallpox - 0,03%/migrant - spreads 1x/day/diseased dwarf/touch - permanent, permanent immunity - blisters all over skin (100%), bruising, coughing blood, bleeding (to death). Also small chance of a deity cursing someone with this.

Epidemics:

Influenza - 2%/migrant - spreads 1x/day/diseased dwarf/touch - lasts 1 month, preventable with medicine, no lasting immunity - chance of fevers, nausea, slight pains all over
Meningococcal meningitis - 0,75%/migrant - spreads 1x/day/diseased dwarf/touch - lasts 1 month, preventable with medicine, no lasting immunity - fever and strong pain, chance of unconsciousness, tiny chance of psychosis
Pneumococcal pneumonitis - 1%/migrant - spreads 1x/day/diseased dwarf/touch - lasts 1 month, preventable with medicine, no lasting immunity - fever and coughing blood, small chance of lung necrosis leading to death

Noncontagious diseases:

High blood pressure: affects 7,5% of dwarves - does not spread - permanent, treatable with blood pressure medicine - if untreated, 33% chance of dizziness lasting one month per month, 1% chance per month of cerebral infarction leading to permanent unconsciousness
Paranoid schizophrenia: affects 1% of dwarves - does not spread - permanent, treatable with psychiatric medicine - if untreated, 50% chance of vastly increased creativity for one month per month, 33% chance of no emotions for one month per month, 10% chance of psychosis for one month per month. Grants hidden label: schizophrenic
Liver cancer: affects 1% of dwarves - does not spread - permanent, liver necrosis can be prevented with cancer medicine - if untreated, liver will eventually undergo necrosis.

Developmental disorders:

Gigantism: affects 0,1% of dwarves - does not spread - permanent - dwarf is permanently 2 times the size of regular dwarves and described as "extremely tall". Grants visible label: giant
Dwarfism: affects 0,1% of dwarves - does not spread - permanent - dwarf is permanently 50% the size of regular dwarves and described as "very small". Grants visible label: midget
Congenital blindness: affects 1% of dwarves - does not spread - permanent, treatable with MEDICINE_MIRACLE if defined - dwarf is permanently blind. Grants visible label: blind

Abnormal psychology:

Insomnia: affects 1% of dwarves - does not spread - permanent, treatable with psychiatric medicine - dwarf cannot sleep for one year and then is somewhat drowsy (and sleeps) for half a year. Grants visible label: insomniac
Depression: affects 2% of dwarves (not as depressed as humans) - does not spread - permanent, treatable with psychiatric medicine - unless treated, dwarf is emotionless, moves 20% slower and does sloppy work (lower creativity)
Psychopathy: affects 0,1% of dwarves - does not spread - permanent, not treatable - empathy is set to 0. Dwarf is permanently bloodsucker and will sometimes drain sleeping dwarves of blood. Dwarf very occasionally attacks nearby friendly dwarves (or animals), causing them to bleed to death after a while. Grants hidden label: serial killer

Other:

Rabies: initially affects 1% of animals you give it to, can be given to animals only - permanent - affected animal goes berserk at 4 weeks, is labeled as "rabid" and starts spreading it by attack (1 victim/day); can spread it to intelligent creatures as well; victims go through a similar cycle and die at 5 weeks.

Medicine:
MEDICINE_EPIDEMIC: stops epidemics spreading, which makes them go away. The only other way to survive them is to isolate dwarves so they don't keep re-infecting each other.
MEDICINE_BLOOD_PRESSURE: well, just about what you would expect. Makes dwarves not stroke out and become vegetables eventually.
MEDICINE_PSYCHIATRIC: keeps schizophrenic dwarves from acting on their delusions but also lowers their creativity
MEDICINE_CANCER: does not cure cancer, but makes it not destroy organs

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Changelog: New, remade version of https://dffd.bay12games.com/file.php?id=7758 . Keeping the old version uploaded for reference for now, and just in case someone prefers it. No longer uses the clumsy and broken "switches" to cause disease. Trimmed somewhat in other ways too. Epidemic probabilities balanced. Fixed typos.

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Pro tips for players:

- To avoid migrants bringing communicable diseases to your fort, the easiest way by far is to build migrant quarters where they and their animals can be quarantined for 1 month before they are let loose in your fort. However, note that if their race is affected by disease, merchants and invaders can bring epidemics to your fort too! Strategic merchant containment is also a possibility, and may even be safer for you for other reasons as well - if they die of pneumonia they caught from your dwarves, you will get the blame (but also the goods, so there's that).

- You can tell if an animal has rabies, because once it goes berserk, it and its corpse should be marked as "rabid". If there is a rabies outbreak in your fort, don't feel too bad. It will have infected only a few other creatures unless you were really unlucky. Isolate everyone who was in contact with that animal, and observe them for 1 month. Some will die, but because rabies becomes contagious very slowly, there should be no further casualties.

- Epidemics are not as bad as you would expect, and spacious fortress design offers significant benefits now. Dwarves tend to be somewhat apart from each other and epidemics just sometimes die out and vanish without you doing anything if people aren't just chilling in a crowded dining hall. But in an overcrowded, small fort, well... you're going to have meningitis, pneumonia and flu bonanza. And vomit all over your hallways. However...

- Now that there are diseases, large and well-stocked hospitals are a thing. Hospitals should have plenty of medicine, wards where disease-bearing dwarves can be contained and observation chambers for dwarves who were in contact with a rabid animal. For epidemics, lock everyone in the infectious disease ward and feed them medicine until the epidemic has stopped. Unless you made wine lower blood pressure or are really good at micro, you'll also probably eventually have a collection of dwarves who had a stroke (but the chances of stroke are only 0,075% per month per dwarf, so not too many). Consider magma-based euthanasia unless you really love those dwarves. Important dwarves who you know have blood pressure could have their own chambers have stockpiles of blood pressure medication.

- The same goes for asylums. Schizophrenic dwarves should have their own little fort stocked with medicine so they can live relatively normal lives. However, since their occasional bonus creativity improves item quality, you may instead take the risks involved and let them live among your dwarves normally, preferably working as craftsdwarves - but they may eventually do something unwise. It's not particularly humane, but if you surround their craftsdwarf's workshop with cage traps, you'll most likely catch them if/when something goes wrong and can release them once they come back to their senses.