Disease

Disease plays a large role in Crusader Kings II, due to the lethality of ailments in the Middle Ages, and generally bad side effects they give to the player character. Most characters are capable of living through the majority of diseases, though some may still die when an outbreak occurs.

All diseases are represented by health traits.

Normal diseases

	Disease	Description
	Generic Illness	The most simple type of "disease," the trait ill reduces martial by 1, health by 2, and fertility by 10%. Unless the ill person in question is very old, weak, or has another disease, the odds of someone dying from this trait is very low. Generic illness and pneumonia are mutually exclusive. It is needed to have a health level of at least 3 to recover from this disease. If The Reaper's Due Expansion is active, the illness trait is replaced by symptoms which will be treated by a court physician.
	Pneumonia	Incompatible with ill, the pneumonic trait is far far more deadly. It reduces all attributes by 2 and reduces health by 4. It also reduces fertility by 50%, making most characters very unlikely to procreate. The trait is often deadly; do not expect to have player character rulers survive this one every time. It is needed to have a health level of at least 4 to recover from this disease.
	Leprosy	Another moderate disease, leprosy makes holding a large kingdom or empire together very difficult. It reduces diplomacy and health by 2, and fertility by 20%. It also reduces sex appeal by 50, and all vassals opinions of their liege by 20. Though leprosy has a +10 bonus with other lepers, chances are that a character will not make use of that bonus often. It is needed to have a health level of at least 4 to recover from this disease. There is a chance to remove this disease by choosing the Theology focus.
	Great Pox	A moderately dangerous disease, syphilis reduces all attributes by 1, health by 2, and fertility by 20%. Furthermore, it reduces sex appeal of the character by 30. This disease will most likely shorten the lifespan of the player character, though it will not necessarily result in an abnormally early death. One of the most dangerous features of this disease is that it can be passed down to children if one of their parents has this trait. This makes long-lived heirs more rare if the ruler suffers from great pox. It is needed to have a health level of at least 6 to recover from this disease. There is a chance to remove this disease by choosing the Theology focus.

Epidemic diseases

Epidemics begin with an outbreak in one province, and can spread through adjacent provinces on the first day of each month.

When a county is affected by an epidemic:

• A dark green cloud appears over the city sprawl
• Characters living in that province will randomly become infected. Characters who have already contracted and recovered from the disease are immune, with the exception of the great pox
• City tax income is reduced
• Supply limit is reduced, and attrition is greatly increased for troops in excess of the supply limit. These effects make warfare harder, especially when large armies are required or multiple diseases are present.

Rulers can protect themselves against epidemics by relocating their capital or by sending individual characters to other locations. Children aged 6-15 can be sent for education to other courts. Adults can lead troops or perform council missions in safer provinces. With The Reaper's Due, it is worth noting that only land provinces are safe: leading troops at sea while an epidemic ravages your capital is a sure way to contract Scurvy ; going into seclusion can be considered a viable alternative.

Conversely, sending a character to an infected location can serve as a quiet way to dispose of a rival or an unwanted heir.

Outbreaks always begin in coastal cities. Cities with higher income are at higher risk. A capital which is far inland may be safer. The Black Death historically arrives around 1300-1400 AD, though the player can change it on the game rules panel at the beginning of a campaign.

Take caution when having your capital on a coastal trade post province since disease seems to have a higher chance of spawning there. More importantly it appears that your Hospital level is NOT checked when the disease appears as would normally occur if it's not in a disease spawn site.

It also seems diseases spread through trade ports in the same network.

List of epidemic diseases

	Epidemic	Contagiousness	Outbreak	Duration	Trait	Effects	Recovery MTTH (for 45yo with 5 base health)
	Consumption (AKA Tuberculosis)	30%	1.2%	30 months		-2 health	24 months
	Slow Fever (Typhoid Fever)	30%	1.2%	30 months		-3 health, -10% fertility	4 months
	Camp Fever (Typhus)	50%	4%	10 months		-4 health, -20% fertility	12 months
	The Plague (Bubonic Plague, Black Death)	95%	1%	10 months		-7 health	3 months
	Measles	60%	3%	8 months		-2 health	5 months
	Smallpox	50%	8%	8 months		-3 health, -25% fertility	5 months
	Great Pox (Syphilis)	50%	8% ( Sunset Invasion)	8 months		-2 health, -20% fertility	Recovery ONLY with Possessed trait

With Reaper's Due expansion

With The Reaper's Due active, the disease system becomes more complex. Characters will first contract symptoms which will then be diagnosed by their court physician. Hospitals can be built to fight epidemics at the province level and the epidemics also affect the level of prosperity in a county.

An infection can develop after being Wounded or Severely Injured . They can be dangerous as a court physician cannot treat this symptom; the player character may have to make up for the lost health by other means. However, it will heal on its own given enough time, just like other diseases. Counter-intuitively, an infection arising from being Severely Injured is less dangerous than the same trait arising from Wounded ; this is because the infection actually replaced Severely Injured (with no net health decrease), but is added on top of being Wounded .

Outbreaks

Outbreaks can begin in any province, and may spread through single ocean tiles. Infected provinces tend to lose prosperity and may experience its opposite: depopulation. Basic hospitals provide minor protection from depopulation.

Upgraded hospitals can also prevent the county from becoming infected. This makes them useful not only in your capital but also in provinces near your capital, especially at chokepoints such as the Grisons-Lombardy mountain pass.

Certain events may reduce a province's disease resistance: a smugglers' ring forming and refusal to pay for a hospital's upkeep. High prosperity also lowers disease resistance.

The Black Death is larger and more deadly, and gets a chance of major outbreak to occur 200 years into any game, regardless of start date. (This can be changed on the game rules panel.) After a major outbreak has happened, the disease becomes endemic and may break out again, but likely on a smaller scale. The Black Death has special patterns. It may miss India, Africa, Scandinavia, Britain, or the Steppes. It also has a chance to miss a discontiguous region called the Historical Plague Exclusion Zone. Once you see evidence of which regions it is skipping, try to move your capital there.

Epidemics can never spread to Iceland, because it does not share any sea zones. However, Iceland is a small duchy in a weak de jure empire, so moving your capital there may reduce both demesne levies and vassal levies. Iceland is also far from everything else, increasing the risk of independence factions.

Seclusion

Rulers receive the option to go into seclusion when an epidemic spreads to counties near their capital. Alternatively, rulers with the Paranoid trait can go into seclusion at any time. Rulers must be landed or patricians to shut the gates. Once the option to go into seclusion is taken, the ruler is isolated together with their courtiers.

All secluded characters receive a -5 penalty to their Diplomacy attribute, and can no longer lead armies (if previously able to) or perform jobs (if they are councilors). If the period of seclusion is too long, negative events may occur, and may result in characters obtaining the Cannibal trait, becoming Craven and experiencing food shortages.

Seclusion may fail if a courtier is exposed to the outside world or contracts a disease before becoming secluded. To mitigate the risk of seclusion breaches, the ruler may get opportunities to kick out courtiers who are displaying symptoms or who have Bubonic Plague. Closing the gates early and keeping a small court can help prevent the disease from spreading unchecked within the secluded court.

Upon opening the gates, the ruler gets the Abandoned the commoners modifier. While this modifier is active (1 year), they have -10 general opinion and cannot shut the gates again.

Known Bugs/Features:

If while secluded, you ask a courtier to your court or marry someone so they come to your court - and they are not already secluded then they will not be secluded in your court. Also, children belonging to another court but with a guardian in your court do not go into seclusion. Both of these can be very bad during the Black Death - such characters will likely die.

If you are a vassal with shut gates and you accept a councilor appointment from your liege your entire court will leave seclusion and you won't be able to shut the gates!

Symptoms

	Name	Command	ID						Health	Opinions	Other modifiers	Possible diseases/Other remarks
	Abdominal Pain	abdominal_pain	215						-1		-10% Fertility
	Chest Pain	chest_pain	211						-2		-10 Personal Combat Skill
	Cough	cough	207	-1					-0.25	-5 Attraction
	Cramps	cramps	212		-2				-0.5		-10 Personal Combat Skill
	Diarrhea	diarrhea	209		-2		-2		-1	-5 Attraction	-20% Fertility -1 Personal Combat Skill
	Fatigue	fatigue	216	-1			-1		-0.25		-20 Rationality
	Fever	fever	208			-1		-1			-10% Fertility -10 Personal Combat Skill -10 Rationality
	Headache	headache	214	-1		-1		-1	-0.5		-10 Personal Combat Skill -10 Rationality
	Infection	infection	218	-3	-3	-3	-3	-3	-2	-10 Attraction	-10 Personal Combat Skill	None Can appear while Wounded or Severely Injured ;adds to Wounded but replaces Severely Injured
	Malaise	malaise	217						-0.75
	Rash	rash	213						-0.5	-5 Attraction	-10% Fertility
	Vomiting	vomiting	210	-2			-2		-1	-5 Attraction	-30% Fertility -10 Personal Combat Skill

Diseases

	Name	Command	ID						Health	Opinions	Other modifiers	Miscellaneous	Cost
	Aztec Disease	has_aztec_disease	132	-3	-2	-2	-3	-2	-4	-10 Attraction -5 General	-30 Personal Combat Skill -20% Fertility -3 Personal Combat Skill	Epidemic (after Aztec arrival)
	Camp Fever	has_typhus	36	-1		-2	-1	-2	-4		-20% Fertility -40 Personal Combat Skill	Epidemic
	Cancer	cancer	230						-3		-20% Fertility	More likely when old aged
	Consumption	has_tuberculosis	34	-2		-1	-2		-2		-25 Personal Combat Skill	Epidemic
	Dancing Plague	dancing_plague	235	-1	-1	-1	-1	-1	-2		+25% Fertility	Epidemic (rare)
	Dysentery	dysentery	226		-1		-1		-4	-15 Attraction	-25% Fertility -20 Personal Combat Skill
	Flu	flu	225	-1	-1	-1	-1	-1	-2	-10 Attraction	-10 Personal Combat Skill	Common and brief
	Food Poisoning	food_poisoning	228	-2	-2	-2	-2	-2	-3	-15 Attraction	-50% Fertility -10 Personal Combat Skill
	Gout	gout	227	-2	-1				-2		-20 Personal Combat Skill
	Has Great Pox	syphilitic	27	-1	-1	-1	-1	-1	-2	-10 Attraction -5 General	-20% Fertility	10% Inherit Chance	-44
	Has Slow Fever	has_typhoid_fever	35		-2		-1	-1	-3		-10% Fertility -40 Personal Combat Skill	Epidemic
	Ill	ill	25		-1				-1		-10% Fertility -10 Personal Combat Skill	With The Reaper's Due DLC, the Ill trait is replaced by symptoms
	Leper	leper	28						-1.5	-15 Attraction -20 General	-95% Fertility -25 Personal Combat Skill
	Measles	has_measles	38			-2		-1	-2		-10% Fertility -30 Personal Combat Skill	Epidemic
	Pneumonic	pneumonic	26	-2	-2	-2	-2	-2	-4		-50% Fertility -35 Personal Combat Skill
	Rabies	rabies	229	-3		-2	-3	-2	-7	-20 Attraction -5 Vassal	+30 Personal Combat Skill -50 Rationality
	Scurvy	scurvy	238	-1	-1	-1	-1	-1	-3		-20 Personal Combat Skill	Gained when leading troops at sea. More likely after 3 years at sea. More likely when an epidemic is ravaging your capital	-35
	Sickly	sickly	144						-2.5			Children can be born sickly. Removed between the ages of 2 to 6
	Smallpox	has_small_pox	39	-2		-1		-2	-3		-25% Fertility -100 Personal Combat Skill	Epidemic
	The Plague	has_bubonic_plague	37	-2	-3	-2	-3	-2	-7		-50% Fertility -100 Personal Combat Skill	Epidemic (nearly mapwide, many special events)

See also

• Disease modding