Diseases/plagues

Those of you who played civ3 conquests will remember those plagues that came and killed your citizens. Now they've been taken out, but I suggest they be re-introduced, but differently:

1.Every so often, a disease/plague may pop up in a random city, usually an unhealthy one. It would make a huge boost to sickness, maybe +6, +8 or even +10.

2.The plague could spread to other cities, the influencing factors being things like road and sea connections, open borders, trade routes, e.t.c. Walls should decrease the chances of a city getting the plague, as plague carriers wouldn't be able to sneak in.

3.The healthier a city, the better the chance of it:
a.Not starting the plague.
b.Not getting the plague.
c.Managing to eliminate the plague.

4.There should be an option to quarantine a city, very nearly eliminating the chance of it spreading the plague, and eliminating the plague from the city within 5-20 turns, but it would have bad consequences:
a.The city would lose all trade routes.
b.The city would not grow.
c.The city would not be able to build (as public gatherings to build would spread the disease).
d.No units would be allowed to move in or out of the city.

5.The disease should also have a chance of damagin units, if they're in an infected city.

Yes, I know this would be hard to script, if not impossible, but I'd like to know if it could be done.

Also, this may seem like a game-breaker, but it would only pop up very rarely (every 50-100 turns, if not longer).

EDIT: Extra idea: After having a plague, and losing it, the city becomes immune to that particular disease, but the plague can still come into the city (as in, it doesn't lose health, but the plague's still there). Then you could have things like immune spanish conquistadors bringing disease to non-immune aztecs, for example.

This will make the expansive trait slightly more attractive.

Additions? Criticisms? Praise? Any more would be welcome.

Bast, it would make it more attractive. I feel the expansive trait is weak right now, and this feature would give it some much needed extra value. Plus it makes it more interesting.

I could live with it
thr problem with random events is: they just happen when you really don't need them.
maybe if a city is unhealthy for (100/unhealthiness)turns then there is a chance for a plague
or something like that, something that is a little more under the players control

I like this idea. It adds a little more something so you need to be careful when it comes to internal collapse. Perhaps another penalty for putting a city under quarintine would be severe unhappiness. The immune military units infecting other civs sounds good to. Kind of like an early germ warfare. Which then gives rise to biological warfare too. Maybe with the discovery of Biology you could build biological weapons. A new promotion after Medic 2 could be something that makes units immune to disease. Something like Hazmat suit or something.