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Disease modding

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Diseases are defined in folder common/diseases/.

Configuration key Type Description Example
rip bool
  • If not specified, the disease will be available in both version (with the same values in both) and doesn't need to be set twice.
  • If rip=no, this will exclude a disease from The Reaper's Due disease database, so that there can be two versions of the disease.
contagiousness float Chance that the disease will spread to an adjacent province ? contagiousness = 0.15
outbreak_chance float Chance that a disease will appear in a province.


  • With less provinces, you get much more disease - the vanilla numbers are balanced for vanilla map province count !
outbreak_chance = 0.01
effect modifiers Province modifiers applied during an outbreak.
effect = {
	city_tax_modifier = -0.5
	supply_limit = -4
	max_attrition = 0.05
icon int The index of icon frame in GFX_disease_icons icon = 1
tooltip key Localization key for disease description tooltip = TUBERCULOSIS_INFO
months int Duration of an outbreak. months = 30
trait trait Associated epidemic trait when a character gets the disease. trait = has_tuberculosis
always_get_message bool always_get_message = no
color color Color for epidemics mapmode. color = { 84 171 176 }
major bool major = yes
active bool Whether the disease exists at game start, or needs to get activated via scripting command activate_disease. active = no
timeperiod clause Validity range for the disease.
Key Type Description
start_date date Start of timeperiod
end_date date End of timeperiod
one_only bool Whether the disease will activate multiple times or once in the timeperiod
outbreak_chance float
can_outbreak conditions Global conditions (total_years_played, global flags, game rules, ...)
months int
max_total_provinces int
spread_through_water bool
min_nb_province int Ignored if 0.
max_nb_province int Ignored if 0.
province_infection_duration int
outbreak_scenario int Detailed scenario of epidemics progression, with starting provinces(start_provinces) and excluded geographical regions (excluded_regions)
timeperiod = {
	start_date = 769.1.1
	end_date = 1452.1.1
	one_only = no
timeperiod = {
	start_date = 1100.1.1
	end_date = 1400.1.1
	outbreak_chance = 0.01
	can_outbreak = {
		total_years_played = 25
		NOT = { has_global_flag = black_death_happened }
		has_game_rule = {
			name = epidemics
			value = delayed_dynamic
	min_nb_province = 1
	max_nb_province = 15
	one_only = yes
	province_infection_duration = 36
	outbreak_scenario = { # Classic plague
		chance = 0.30
		start_provinces = {
		excluded_regions = {
yearly_province_pulse commands
character_infection_chances clause
character_infection_chances = {
	months = 3
on_character_infection commands Scripted effects to give the epidemic trait to a character. Typically uses a random_list to specify a ratio of randomly affected characters.
on_province_infection commands
disease_gfx disease_gfx = disease_gfx_typhoid_fever
max_total_provinces int max_total_provinces = 5
spread_through_water bool spread_through_water = no
min_nb_province int Ignored if the given value is 0. min_nb_province = 1
max_nb_province int Ignored if the given value is 0. max_nb_province = 1


There a a few ways that events can interact with epidemics:

  • activate_disease = <disease_name> will allow diseases that are off by default to spawn randomly or via scripting.
  • reduce_disease = <double> will weaken an existing epidemic in a province. reduce_disease = 1 should be able to cancel an epidemic in a province.
  • spawn_disease = <disease_name> will start an epidemic in a province.
  • start_outbreak = <disease_name> will start a epidemic using the information defined in the diseases timeperiod entries