How about implemeting other random disasters?

Black death:
-possible after trade and before medicine
-decreases population in all cities linked by trade routes.

Volcanic eruption:
-possible anytime
-forms new mountain, destroying everything in a 4x4 area

Ice age:
-possible anytime before industrialization
-causes areas around mountains to become glaciers/tundra

Earthquake:
-possible anytime before plate techtonics (new tech allows building wonder to prevent earthquakes)
-randomly destoys buildings in a random city.

Asteroid:
-only possible in genetic/diamond age (otherwise would cause end of game)
-increases likelihood of nations accepting cease fires and peace treaties to focus on saving the earth by building a space probe to divert the asteroid.

Other ideas?

But the real fun will be transmission of diseases. Once my civ is hit with flu A and I've suffered the duration, my units carry flu A and intentionally or not pass it to everyone I meet. Maybe we need a special unit (Early Infector) to send disease around. It doesn't take genetic engineering to spread plagues.

The Infector in unit.txt has this:
Plague {
Chance 0.5
Sound SOUND_ID_BIO_TERROR
Effect SPECEFFECT_BIO_TERROR
}
And I see in Orders.txt a
ORDER_PLAGUE {...}
but this doesn't spell out the effects.

So how do we make a new epidemic ?
Can it have attributes (deathrate, onset, duration) created dynamically in the course of the game?
Can diseases affect only cities near swamps or jungles (and not those with hospitals)
And is it possible to indicate that a given civ has been exposed to a given epidemic?
And is it possible to make units carriers and transmit a disease without actually attacking?
Transmission along trade routes would be nice.
(looking to add some germs to our guns and steel)