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%. |
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Pneumonia |
Incompatible with ill, the pneumonic trait is far far more deadly. It reduces all attributes by 2 and reduces health by 4. |
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Leprosy |
Another moderate disease, leprosy makes holding a large kingdom or empire together very difficult. |
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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. |
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 not immune
- 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 
; 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.
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 |  |
-2 health | 4 months |
 |
Camp Fever (Typhus) |
50% | 4% | 10 months |  |
-4 health | 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 | 5 months |
|
Great Pox (Syphilis) |
50% | 8% (  Sunset Invasion) |
8 months | |
-3 health, -20% fertility | Recovery ONLY with  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 
can develop after being 
. 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.
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 discontinuous 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 
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 
trait, becoming 
and experiencing food shortages. The ruler can also kick out any courtier who displays any symptoms of disease. Seclusion may fail if a courtier is exposed to the outside world or contracts a disease before becoming secluded.
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.
Symptoms
| 名称 | 键值 | ID | 
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健康 | 好感 | 其他修正 | 可能的疾病/其他注释 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
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腹痛 | abdominal_pain | 215 | -1 | -10% 生育能力 |     
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胸痛 | chest_pain | 211 | -2 | -10 个人实战能力 |  
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咳嗽 | cough | 207 | -1 | -0.25 | -5 吸引力好感 | 
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抽筋 | cramps | 212 | -2 | -0.5 | -10 个人实战能力 |  
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腹泻 | diarrhea | 209 | -2 | -2 | -1 | -5 吸引力好感 | -20% 生育能力 -1 个人实战能力 |
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疲乏 | fatigue | 216 | -1 | -1 | -0.25 | -20 理性 |  
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发热 | fever | 208 | -1 | -1 | -10% 生育能力 -10 个人实战能力 -10 理性 |
 
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头痛 | headache | 214 | -1 | -1 | -1 | -0.5 | -10 个人实战能力 -10 理性 |
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感染 | infection | 218 | -3 | -3 | -3 | -3 | -3 | -2 | -10 吸引力好感 | -10 个人实战能力 | 无 或  时可能出现；添加在 之上但替代
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不适 | malaise | 217 | -0.75 |
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皮疹 | rash | 213 | -0.5 | -5 吸引力好感 | -10% 生育能力 |
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呕吐 | vomiting | 210 | -2 | -2 | -1 | -5 吸引力好感 | -30% 生育能力 -10 个人实战能力 |
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Diseases
| 名称 | 键值 | ID |
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健康 | 好感 | 其他修正 | 杂项 | 费用 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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阿兹特克梅毒 | has_aztec_disease | 132 | -3 | -2 | -2 | -3 | -2 | -4 | -10 吸引力好感 -5 大众好感 |
-30 个人实战能力 -20% 生育能力 |
 瘟疫（ 日落入侵之后）
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露营热 | has_typhus | 36 | -1 | -2 | -1 | -2 | -4 | -20% 生育能力 -40 个人实战能力 |
 瘟疫
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癌症 | cancer | 230 | -3 | -20% 生育能力 | 老年更可能获得 | |||||||
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肺痨 | has_tuberculosis | 34 | -2 | -1 | -2 | -2 | -25 个人实战能力 |  瘟疫
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舞蹈瘟疫 | dancing_plague | 235 | -1 | -1 | -1 | -1 | -1 | -2 | -25% 生育能力 | 瘟疫（稀少）
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痢疾 | dysentery | 226 | -1 | -1 | -4 | -15 吸引力好感 | -25% 生育能力 -20 个人实战能力 |
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流感 | flu | 225 | -1 | -1 | -1 | -1 | -1 | -2 | -10 吸引力好感 | -10 个人实战能力 | 常见且短暂 | |
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食物中毒 | food_poisoning | 228 | -2 | -2 | -2 | -2 | -2 | -3 | -15 吸引力好感 | -50% 生育能力 -10 个人实战能力 |
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痛风 | gout | 227 | -2 | -1 | -2 | -20 个人实战能力 | ||||||
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梅毒 | syphilitic | 27 | -1 | -1 | -1 | -1 | -1 | -2 | -10 吸引力好感 -5 大众好感 |
-20% 生育能力 | 10% 几率继承 | -44 |
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慢性热 | has_typhoid_fever | 35 | -2 | -1 | -1 | -3 | -10% 生育能力 -40 个人实战能力 |
 瘟疫
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身患疾病 | ill | 25 | -1 | -1 | -10% 生育能力 -10 个人实战能力 |
拥有 死神索命DLC， 特质被症状替代
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麻风病人 | leper | 28 | -1.5 | -15 吸引力好感 -20 大众好感 |
-95% 生育能力 -25 个人实战能力 |
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麻疹 | has_measles | 38 | -2 | -1 | -2 | -10% 生育能力 -30 个人实战能力 |
 瘟疫
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肺炎 | pneumonic | 26 | -2 | -2 | -2 | -2 | -2 | -4 | -50% 生育能力 -35 个人实战能力 |
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狂犬病 | rabies | 229 | -3 | -2 | -3 | -2 | -7 | -20 吸引力好感 -5 封臣 |
+30 个人实战能力 -50 理性 |
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坏血病 | scurvy | 238 | -1 | -1 | -1 | -1 | -1 | -3 | -20 个人实战能力 | 在海上领导军队时获得 在海上3年后更可能获得 一种瘟疫在你的首都肆虐时更可能获得 |
-35 | |
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多病 | sickly | 144 | -2.5 | 儿童出生可能就多病 2至6岁间移除 |
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天花 | has_small_pox | 39 | -2 | -1 | -2 | -3 | -25% 生育能力 -100 个人实战能力 |
 瘟疫
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黑死病 | has_bubonic_plague | 37 | -2 | -3 | -2 | -3 | -2 | -7 | -50% 生育能力 -100 个人实战能力 |
 瘟疫（几乎全图，许多特殊事件）
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