Desease could also be created by the element water, air and earth. Maybe fire, but I don't find a reason...

A desease can come from contaminated water, stinking air or overflowing drainage system (earth/mud).

The cure can come from 'holy water', 'healing plants' (earth)

I think, we could find a way for every element to create or cure a desease...

I'd love to see a more involved natural disease system in place. Lots of games take it into account, including Civ and Total war, but like you said it's usually just an abstract factor considered in population growth/loss. One notable example are the plagues in Medieval II: Total War. There, individual cities can be struck by plagues and affects their populations and all garrisoned units. If you move one of those garrisoned units to another city there is a good chance that the plague will be transfered with them; and military units as well as special units like diplomats, spies, generals, etc, can all be killed by the plagues.

With the planned caravan system this would become even more important. In order to prevent spreading the plague from one city to another you'd have to quarantine it; but if the city isn't capable of self-supporting its own population you might want to send in some shipments to prevent a total disaster (this actually wouldn't need to spread the plague, but if there's a max # of caravans you can have it might tie some of them up until you let them leave). Or, if the plague-stricken city is responsible for the majority of a key resource or product, you might want to risk shipments out of the city, which would be a major risk.

That said, if they do implement natural disease in such a comprehensive manner I'd like it to be optional. Sometimes I like being able to build vast, sprawling cities with huge populations without having to worry about such petty things as disease  

For fire you could do something like Heat wave (Global Warming?) that could cause famine resulting in starvation. Not a disease but it would have the same end result on population.

For fire you could do something like Heat wave (Global Warming?) that could cause famine resulting in starvation. Not a disease but it would have the same end result on population.

I agree with what you are saying - you don't want every element to have the same net effect but in different packaging. So maybe the heat wave would affect food production (as opposed to wiping out population directly), with only water countering it. Maybe the Heat wave would make some squares (like Tundra) more productive so if it was a global effect it would help some areas and hurt others. Or if it was a more localized effect it could still be used as either beneficial or harmful depending on the terrain it was cast on. So I think it would behave quite differently than a "plague" but could still be countered (by water, obviously) and would be a nice analogous spell, for balance, to the other elements' "plague". Another solution to the Heat wave as a negative effect would be to have trade in place to get food into the affected area.

diseases and such are a major problem for mideval civilizations, so that seems like that would be a reasonable random event.  I think it would really set the flavor for struggling to rebuild the world, since once population gets to a big size a disease is very likely.  

Making it a spell just lets you spread out the features.  So if you make a diseased animation and all that for cities, it will be worth the time and effort.   no matter what it is a little bit of feature creepy (since its something special, everything that isn't a main feature is feature creep) but it spreads it out to make it make it I think worth it.    I vote there should be some sort of disease feature

yeah, okay diseases would be cool but only as long as they don't dominate my game time. I'd like the diseases to scale according to early-middle-late game (and relative size of the game). Tie naturally occuring diseases into population size/density and make them increase in likelyhood depending on city size/health/etc. Some buildings to help prevent the spread or mute the affects will aslo be necessary (somebody said apothecary and herbalist, good ideas). I'm not sure I like the idea of being able to transfer disease (mistakenly or not) via trade or resource caravans to your other cities. However, i'm not 100% here, maybe if there was an interesting way to go about preventing it from happening (ie so that it's not automatic) like using a curative spell on caravans coming from that particular city. But i do like the idea of being able to send a naturally occuring disease to an opponent's (enemy or ally) city.

and i certainly don't want to see Channellers casting R Jordan's 'albino midget disease' after 4 turns. 

I do like the idea of Channellers being able to access 'disease' spells at some point in the game, maybe even 'sickness' early on (maybe that's an unnecessary distinction but you get what i mean). And counter-spells would be required. I would like to see some generic curative spells that can take the edge off the more serious 'disease' spells. I'm not saying they should be cheap nor that they would eliminate the ill effects, just that they should reduce its affects and can be used on diseases or sicknesses generally (and specifically can help prevent the spread of some diseases)

I think deseases could also be harmless. We are only talking about disastrous deseases which kill people. But there also can be deseases which are not that harmful but cause negativ effects.

There could be a bad acne, which reduces the population grows, because no one likes each other anymore. A psychological desease would do the same. A desease which causes health problems, can bind the people to bed, so no one will produce anything anymore until they are cured, because no one was killed.

Effectively, reducing the population creates the same effect.(Don't forget, popultaion numbers are, normally, a simplification of an enourmously complex piece of information)

Medieval disease was usually the result of large population growth without proper sanitation infrastructure being put in place to cope.

As an example. The "Black Plague" of Europe was not "caused" by rats, the rats were simply the spreading agent of the outbreak. The "cause" was the abhorent piss poor sanitary practises in the major cities of Europe of the time.

In game, if not by Magic means, disease could be added to the Pop. as a result of not having the proper controls in effect. I build a city and it Pop. grows and grows but if I do not buy that one Tile (whatever that tile would be) that will maintain that Pop. level, until the next growth level is met, disease begins to take hold. It's most direct effect would be an ability to re-inforce your armies, as they are built directly from your cities Population base.

Complexity is fine, but I would agree with the idea that if it gets put in, it has to be dealt with easily, and perhaps have a heavy cost factor on either end of the whole "do I really need it" vs the "what is the cost of not having it"...

Well, europe was actually better than parts of asia at the time, where I guess sanitation must have been worse.   The black plague actually caused less deaths in europe than the 30 years war (which was happening around the same time, and often the black death gets deaths added to its toll because it gets lumped with the war).

For some reason people always think of europe when somebody says "black plague" even though it started and killed more people in asia.  We (as western culture) just have for europe records of it taught to us I guess.

But yes, the point is that it would be interesting.

In Civilization IV, you have the health of a city, and it doesn't really do much except adjust population growth if you can't meet health requirements.   If we had a similar mechanic, then a major disease outbreak could have a chance to occur whenever there is a lot of unhealth in a city (of course the spell would force it)

If disease can spread, it should be limited by race.   maybe not much of a factor since both men and fallen are (or at least were) human.    If we sued classic MoM races though (or for the sake of user created ones) things like Beastmen, Klacken, trolls, and dragon-guys (forgot name) shouldn't be able to get the same diseases as regular humans since they are so far detached.  (i'd say that beastmen, trolls, and dragon-guys could have the same since they are from the same world and in theory of similar ancestery.  There are no humans are myrror by nature and most of arcana's races are human-like, klacken and lizard men being the exceptions)

In truth I was annoyed by Civ IVs interpretation of "health" in game. I thought that it was far too common for your cities to be emitting green smoke, because you didnt have the right resources or improvements... which was a major turn off in a visual aspect especially  not to mention infuriating that as you played on harder difficulty levels it just got harder to maintain!

On another note, I would be happy to see specific diseases caused by magic and even by terrain like in Civ IV... just as long as its not showing my city stinking up the countryside ill be happy Anyone else agree this was annoying to watch?

I wouldn't want to be clearing up after disease all the time, in the same way that I hate it in the Total War games when I'm constantly struggling against rebellion as I approach the 50-province mark. Or the stupid stack of workers automated to clean pollution in Civ 3. I'm not saying that this is what anyone's suggestions are leading to, just that it needs to be kept in mind.