Disease Model v1.3

Method I (Civ-based distribution)

Best used for a more balanced, though less realistic, full-world game or scenario.

The Disease Pools

To determine what diseases a culture starts with, disease pools will have to be established first. There will be an unlimited number of disease pools. The size and location of the disease pools will conform to the following criteria:

-On each continent, all cultures with similar population densities will belong to the same disease pool (if adjacent).

-Islands will belong to whichever continent it is closest to (if within the range of ancient boats, 2 spaces I presume) and whatever population density is closest.

-Island chains will be grouped together as a single disease pool if all islands are within ancient boat range (again, 2 spaces I presume).

Once the disease pools are established, the number of diseases in each disease pool will be established according to the following chart:

-The number of diseases in each pool is:

Climate zone: (band #) # of diseases

Arctic/islands (1,8) 0-1 (leaning toward 0, maybe a 60% chance)

Upper Temp. (2,7) 0-2

Lower Temp. (3,6) 1-2

Subtropical /tropical (4,5) 2-3

Once the number of diseases in each pool has been determined, the diseases that reside in those pools will be distributed as follows:

-Tropical pools will receive only jungle and water-borne diseases.

-Lower Temperate pools will receive only the “normal” and water-borne diseases.

-Upper Temperate pools will receive only the “normal” diseases.

-Arctic pools will receive only “normal” diseases.

-Islands or island chains that count as a separate disease pool will get one disease (if any), and that disease will not belong to any other pool

-Diseases can be “shared” between different, adjacent pools if they still need more to fill in their number of diseases.

-Every disease that is in more than one pool will receive a strain tag (A, B, C, etc.).

Then each culture would get its number of initial diseases from its disease pool.

Initial Diseases

Initial Diseases will represent those the people have previously been exposed to. Every province of every Civ. and barbarian "Culture" in the game will start with at least one of the 19 diseases modeled in the game. This assumes that each different cluster of any barbarian culture will be treated as a different province (ex. If culture #17 were divided by Roman territory, each half would be treated as a different province). By modeling every province rather than the Civ/Culture as a whole we can allow for greater diversity and realism in the system with only a few extra calculations.

To calculate the number of initial diseases a Civ has, we would generate a number (1-10) then modify it by population density and climate. Climate would modify the number based on the zone the Province is located in:

Climate Zone (Band#) Modifier (+/-)

Sub-arctic/Arctic (1,8) 3

Sub-arctic/Upper Temp. 2 (use this if it overlaps both zones listed)

Upper Temp. (2,7) 1

Lower Temp. (3,6) 0

Low.Temp. / Subtrop. -1 (use this if it overlaps both zones listed)

Subtropical/Tropical (4,5) -2

Population Density

Population Density is calculated as follows:

Provincial_Population / Provincial_Size (In Sq. Miles) = Population_Density (# of people per sq. mile)

Pop. Density Modifier (+/-)

Up to .3 2

Up to .6 1

Up to 1.2 0

Up to 2.4 -1

Up to 4.8 -2

Up to 9.6 or greater -3

***Once modified for climate zone and density, the number of diseases is as follows (however the number of diseases cannot exceed the number in the pool):

Modified Number Number of Diseases

1 or less 3 Diseases

2-6 2 Diseases

7-10 1 Disease

More than 10 0 Diseases

Method II (Province-based distribution)

Best used for scenarios with less than an entire world map.

The computer will generate a random location for each disease in the game. These locations (a single province) will be the starting points for the disease, and they will spread from there. The locations will be generated according to the following criteria:

-Tropical provinces will receive only jungle and water-borne diseases.

-Lower Temperate provinces will receive only the “normal” and water-borne diseases.

-Upper Temperate provinces will receive only “normal” diseases.

-Arctic provinces will receive only “normal” diseases.

-A province can be randomly chosen more than once (i.e. have more than one disease.)

Method III (Jungle-based distribution)

Best used for a realistic world game.

The computer will distribute 0-2 (random, leaning towards 1, maybe 60% chance) diseases within a single random province inside each major jungle in the tropics, except for the largest. The rest of the diseases will be placed into the provinces of the largest jungle in the tropics. FE, on earth there are 3 major jungles, Southeast Asia, Amazon Basin in South America, and the Largest being in Central Africa.

Method IV (Emerging)

There are no initial diseases. All diseases will emerge as the game is played, using the emerging rules below.

Disease Table

Key

^ = Water-borne;

$ = Jungle;

Disease Codes (Can either be a single number or range of numbers-shouldn’t be greater than 4; can’t be less than 0. Users should be able to define more codes (“O” and beyond).

A = 0-1

B = 0-2

C = 0-3

D = 0-4

E = 1-2

F = 1-3

G = 1-4

H = 2-3

I = 2-4

J = 3-4

K = 1

L = 2

M = 3

N = 4

*You will notice that not all codes are used in the default game diseases, however they may be used for genetically engineered diseases or those created for scenarios.

Mortality Real World Diseases

Name/ viral, bacterial / rate / Location Code

Bubonic Plague / B / 15-30% / plains near India I

^Cholera / B / 10-20% / Arabia J

^Dysentery / B / 10-20% / Most likely Africa H

$Dengue Fever / V / 10-20% / Most likely Africa B

^Diphtheria / B / 5-10% / Most likely Africa F

Hantavirus / V / 15-30% / plains near India H

Influenza / V / 1-20% / Europe A

Leprosy / B / 1-2% / Arabia A

$Malaria / V / 5-10% / African jungles C

Measles / V / 1-5% / Arabia/Egypt A

$Sleeping Sickness / V / 5-10% / African jungles B

Smallpox / B / 5-10% / Arabia/Egypt D

Syphilis / B / 1-5% / America/Caribbean A

^Tuberculosis / B / 5-10% / Europe E

^Typhus / B / 5-10% / Europe C

Whooping Cough / V / 1-5% / Europe C

$Yellow Fever / V / 5-10% / Most likely Africa B

How Disease Works

For every disease a province has it will also have a resistance number for that disease. There will also be a strength number (str.) for each disease. It is by comparing these two numbers we will determine what effects a disease will have:

-If disease str. is equal to or less than the province's resistance:

STR % pop. Loss

Equal .05% (5 “heads” per 10 million)

1 less .04% (4 “heads” per 10 million)

2 less .03% (3 “heads” per 10 million)

3 less .02% (2 “heads” per 10 million)

4 less .01% (1 “head” per 10 million)

5+ less no loss

*The disease code, multiplied by .01, is added to these figures.

**The player would not be alerted to these deaths because it isn't an epidemic; it’s just the natural course of the disease. These would, however, show up in a population losses chart (that would include all causes of death, not just disease based), which the player should be able to access, each turn if he so desires. **

-If disease str. is greater than the culture's resistance, a percentage check for an epidemic is made. This % chance is equal to 3 times the difference between str. and resistance (may need to be adjusted during play testing).

-If there is an epidemic, there is a loss of population equal to the mortality rate generated for the disease plus the difference between resistance and disease STR. This loss is for one turn only.

-If there is no epidemic, there is population loss as though the str. were equal to the resistance (.05% plus {the disease code * .01} plus [the amount str. is greater than resistance * .01]). FE, if disease str. is greater than resistance by 2 and the disease code generated was 2, then population loss would be .09%, (.05 + {2 * .01} + [2 * .01])

An example of how disease works: (hasn’t been updated yet)

Civ A and Civ B meet for the first time {Civ A has Smallpox (str. 12, resistance 14) and Civ B has Hantavirus (str. 10, resistance 10)} and each give the other it’s initial disease. Let’s take a look at what will happen the 3 turns after both diplomats (armies, explorers, etc.) end their own turns in their own home Civ. We’ll assume one province with 10 million people for each Civ.

CIV A-- They loose .03% of their population every turn due to smallpox because it is 2 less than their resistance rate. But this turn they also have a new disease, Hantavirus (str. 10), which they have no resistance to. The check is made (3 times the difference of str. and resistance, which is 30% in this case) and a 17 is generated, we have an epidemic, so they loose an additional 20% (let’s just assume that the computer randomly generated 20% because it’s between the range, 15 to 30 percent, listed for the mortality rate on the chart). In addition to that 20%, because this is an epidemic, we must add the difference of str. and resistance, which is +10 in this case, which brings us up to 30%. So that’s a total of 30.03% of population loss, or 3,003,000 people (3,000,000 for Hantavirus and 3000 for smallpox). Then the next turn, their resistance for Hantavirus will go up from 1 to 5 (randomly determined). Disease str. will still be greater than resistance so the epidemic may continue. Let’s assume a 5 was generated and now their resistance to Hantavirus is 5. This time the check is made (3 times difference, which is now 15%) and a 74 is generated, no epidemic this time. Then on the third turn after acquisition a 16 is generated, still no epidemic, but they still continue to loose people from smallpox. That’s a grand total of 3,009,000 people lost.

CIV B—They loose .05% of their population every turn due to Hantavirus because it is equal to their resistance rate. This turn they also have a new disease, Smallpox (str. 12), which they have no resistance to. The check is made (3 times the difference of str. and resistance, which is 36% in this case) and a 49 is generated, we have no epidemic, so they loose 5000 due to Hantavirus but none for smallpox. Next turn another check is made this time a 28 is generated, and now we have an epidemic. They loose an additional 6% (let’s just assume that the computer randomly generated 6% because it’s between the range, 5 to 10 percent, listed for the mortality rate on the chart). In addition to that 6%, because this is an epidemic, we must add the difference of str. and resistance, which is +12 in this case, which brings us up to 18%. So that’s a total of 18.05% of population loss, or 1,805,000 people (1,800,000 for Smallpox and 5000 for Hantavirus). Then the next turn, their resistance for smallpox will go up from 1 to 5 (randomly determined). Disease str. will still be greater than resistance so the epidemic may continue. Let’s assume a 3 was generated and now their resistance to smallpox is 3. This time the check is made (3 times difference, which is now 27%) and a 15 is generated, the epidemic continues. This time the computer generates a 10% for mortality rate (the maximum for smallpox), so that’s 10% plus the difference of nine, or 19%. That’s a total of 19.05% of population loss this turn, or 1,905,000 people, for a grand total of 3,710,000 people lost in the 3 turns following the acquisition of smallpox.

Some other things to keep in mind:

-Base resistance is 0 for all diseases, except initial diseases, which are 10.

-Base disease str. is 1-5 plus the disease code.

-After an epidemic occurs, resistance increases by 1-5

-Jungle and Water-borne diseases can only affect the climate bands 3 through 6

-With the discovery of genetic engineering a Civ could create new diseases or more powerful strains of existing diseases for use in biological warfare. We do need to make sure that the AI for other civs understands the risks associated with this. They would be just as susceptible to the engineered disease also, unless they made themselves a cure first…

On the genetic engineering “Create-a-disease” screen, the player will be able to choose all of the disease’s traits (including it’s name). He will not enter exact numbers, but will instead choose from phrases. For example, for a disease’s str. he could choose, “strong”, “very strong” etc. or for a disease’s evolution rate (disease code) he could choose, “slow”, “rapid”, “very rapid” etc. Each choice will affect the “cost” of researching the disease, and therefore how long it takes to develop. Higher settings will cost more R&D, FE; a “very strong” disease will take more R&D than a “weak” one. The player will also be able to modify existing diseases. Here he will not choose the settings, but rather modify them. FE, he would choose a disease from the list, then click a button to make it either stronger or weaker, faster evolution or slower evolution, etc. This modified disease would retain its name, but have a number tagged onto the back of the name, FE, Smallpox 3 could be an engineered disease.

Disease when years per turn changes:

# Of years per turn / range
10 / range of 2 turns
5 / range of either 3 or 4 turns (determined randomly)
1 / range of 5 turns
* I'm using Civ years per turn here since I assume we'll do something similar.

What all that means is when there are 10 years per turn the death caused by an epidemic will be spread over 2 turns. An example:

You have 10,000,000 people in the province when an epidemic of Ebola hits. The mortality rate for Ebola (15 to 30% range) is determined just like before and let's assume a 30% mortality rate was generated. Now that's 3,000,000 people who will die from the disease. But because there are 10 years per turn now, these deaths will be divided between 2 turns. 75% (2,250,000) of these 3 million will die the first turn and the other 25% (750,000) the second.

The same technique will be done when years per turn reaches 5 years or 1 year per turn. The following chart shows the percentages of pop. loss for each category of "years per turn."

Years per turn	1^st Turn	2^nd Turn	3^rd Turn	4^th Turn	5^th Turn
10	75%	25%	---	---	---
5 (3 turn spread)	60%	25%	15%	---	---
5 (4 turn spread)	50%	20%	20%	10%	---
1	40%	20%	20%	10%	10%

Spreading Disease

Whenever any kind of contact is made between two Civs/cultures (merchants, armies, migrations, etc.) there would be a chance of the disease spreading. Also when a unit encounters jungle, there will be a chance of it catching a jungle disease (that the province contains) and possibly bringing it back to its homeland.

When contact occurs, including jungle travel, the percentage chance of catching the disease is the square root of [.001 multiplied by the number of people making contact (only the people in the square count, not the entire province)]. The level of resistance modifies this percentage —for every 10 levels add 1% (may need tweaking) to the final number. Only one disease can spread per contact. So for example, if a Greek army of 10,000 men landed in Egypt, at a square that had a population of 70,000, there would be an 8% chance (modified by the Egyptian’s resistance to whatever disease is trying to spread) of an Egyptian disease spreading to the Greeks. There would be a 3% chance (modified by Greek resistance to whatever disease is trying to spread) of one of the Greek diseases going to the Egyptians. Since only one disease can spread per contact, there is a 50/50 chance of who gets to “try to spread their disease” first (this, of course, should be determined before the exact chance of spreading percentage is worked out).

So this means you would need a population of 10,000,000 people in a single square to have a 100% chance of spreading a disease (without any modifiers for resistance), which should prevent disease from spreading too fast.

Other Modifiers

-Infrastructure could help reduce casualties of disease (Hospitals and such will reduce Mortality rates).

-Famine will reduce resistance temporarily by 2 on the first turn, while famine continues, by 1 per turn thereafter (these negative modifiers are cumulative).

-Technology- some will have individual effects on diseases, chance of spreading or Mortality rates (like vaccinations will effectively cure viral diseases).

-Some techs will increase the rate of disease str. increases (for example: vaccinations will cause viral diseases to “evolve” at a faster rate, creating super diseases).

Sanitation Levels and Population Density

Disease resistance decreases by the amount listed for a disease’s disease code whenever pop. density increases and/or sanitation levels decrease.

Sanitation Levels

The Health/Water Infrastructure from the economic model defines “Sanitation levels”. If they drop by less than 1/4 of the level needed by the population, then the disease code is applied once. If it drops by less than 1/2 needed but more than a quarter, then the code is applied twice, if it drops more than half it is applied 3 times. As the levels reach what is needed the code is removed (even if this means that the resistance is lower than it was before the sanitation levels dropped). – For Example, let’s say you have the disease Cholera, resistance 30. Let’s also assume you have Heath/Water level of 100, and that is exactly what the populace needs. Now something causes those levels to drop to 80, but you still need 100, since that is less than 1/4 needed, the disease code for Cholera (Code C- a random 1-3) is subtracted from your resistance only once, let’s assume a 3 was determined and now your resistance is 27. Ignoring the possibility of an epidemic, once the Health/Water levels are back to what is needed, the code will be generated again and this time added to your resistance, assume a 1 was “rolled”, your resistance is now 28-, 2 less than before…

* Not sure if we should add the code back to resistance if levels return to “normal”; then it would almost be a good thing: bonus of 1-5 for epidemic and code bonus...is that too much? Even 1-5 may be too much*

Population Density

Population Density is calculated as follows:

Provincial_Population / Provincial_Size (In Sq. Miles) = Population_Density (# of people per sq. mile)

Each square can comfortably hold, without any problems, x people per square mile. As tech levels, such as architecture (for skyscrapers and such) and sanitation, increase this number will also. Each 50% increase of x, beyond x, will cause a +1 to disease str. So for example, if x were 1000, then a population of 1500 would cause a +1, pop of 2000 would cause a +2, pop of 2500 would cause a +3, etc. The “x” still needs to be determined.

Disease Evolution and Emerging Diseases

Emerging Diseases are those that have either evolved from an animal disease to a form that can affect humans or a human disease that has changed into a new strain (usually more powerful, but not always).

In game terms there are two ways in which a new disease may emerge, either based on certain tech levels (domestication, vaccination, etc.) or disease str. vs. resistance levels.

Technology-forced Evolution

*This is where totally new diseases emerge.

The tech stuff will have to wait until the tech model is further along. In general, the chance of a disease emerging based on domestication will decrease as the tech increases, due to less contact between farmers and animals as it is automated. In general, Vaccination and Inoculation will almost certainly cause new strains; it’s just a question of when. I can’t think of any other techs except sanitation that would be involved in this right now.

Disease str. vs. Resistance

The short version of a long, technical story is that when a culture develops sufficient resistance, to the point where little to no people are dying of the disease, the disease organism has effectively lost it’s host species so must either adapt or die out. While the disease is not trying to kill it’s host, and is actually trying to co-exist, it’s the weak hosts who die out – though occasionally a disease is so “powerful” that it must adapt or effectively destroy it’s own host species. So in game terms this means, that for every point resistance is greater than disease str. by, there is a 1% chance that a new disease strain emerges. This check *should not* be performed every turn; every 10 or more should suffice (but will be decided during playtesting).

When str. gets too strong

Like stated above, occasionally a disease is so “powerful” that it must adapt or effectively destroy it’s own host species. If this should occur, for every point str. is above resistance, there is a 1% chance that the str. will be reduced by 1-5. Again, this *should not* be performed every turn; 10, or maybe more should be enough. ** This is nearly impossible with the current model, but should be included as a “fail-safe”, incase it should occur. **

Combating Disease

Very little was known about disease and how they worked early in history, so combating disease was more or less a matter of luck. Though some cultures did develop taboos that helped keep them from harm’s way, such as most Eastern cultures with rats, which helped them, avoid the plague in the middle ages. But these taboos probably came about due to a previous exposure to the disease, so in game terms this is already covered with the bonus to resistance after an epidemic. However, with higher tech levels, you can truly prevent an epidemic.

To keep players from the tedious details of preventing epidemics, the process will be totally automatic, with the player receiving messages about the outcome. A certain level of medical infrastructure and medical tech (summed average of several techs) is needed for prevention to be possible. Then we can either force the player to build a CDC (center for disease control), or assume it is built when these levels are reached.

The prevention can occur either before the epidemic strikes or while it is occurring (when death is spread over turns). When an epidemic strikes a check is made based off of these levels (from paragraph above), and the epidemic is either prevented or not. When death is spread over turns, a check is made each turn before the deaths occur, and if the check is passed, no further loss of life occurs and the epidemic is over.

If the epidemic is prevented before it strikes, the 1-5 bonus is still applied to resistance as though the epidemic had occurred, but no loss of life occurs. If the epidemic is already occurring and the check is made, then no further loss of life occurs, and the 1-5 bonus is still applied. So from the example under “Disease when years per turn changes”:

You have 10,000,000 people in the province when an epidemic of Ebola hits. The mortality rate for Ebola (15 to 30% range) is determined and let's assume a 30% mortality rate was generated. Now that's 3,000,000 people who will die from the disease. But because there are 10 years per turn now, these deaths will be divided between 2 turns. 75% (2,250,000) of these 3 million will die the first turn and the other 25% (750,000) the second. ---- If the check is made when the epidemic first hits, all 3 million people will live, but if it was failed, then passed the second turn, 750,000 people will be saved.

Eradicating Disease

Krenske proposed this multinational “wonder” and I think it is a great idea. However, I don’t see it as a wonder so this is what I propose:

A treaty only allowed under the United Nations or possibly a treaty where one nation would “foot the bill” for the entire undertaking, simply because most countries, I think, would not allow the large amount of people necessary to complete the task into their country for whatever reason. So with the U.N. backing the treaty a disease could be eradicated throughout the world, as smallpox was in real life.

To accomplish this at least one nation would have to have a medical tech level of a certain level (TBD), and the project would also cost lots of money for supplies, etc., along with a number of turns based on the population of the planet at that time. There are still a few details to add to this but I think everyone should get the idea. What do you think?

Strains

Strains are variations of an existing disease that come about either through genetic engineering or disease evolution. They will usually appear later in the game, but there will always be a chance of new strains appearing. See Disease Evolution section.