[Lazy_Perfectionist]

As EA Ctis in DoomChicken, I had those soldiers with the city defense bonus. I also had sufficient bags of wine to prevent starvation. The only way for me to get disease was through leprosy.

Abysia was sieging one of my forts with a large force. Ermor as well at another. I cast Leprosy on my province under siege. They got diseased, I did not.

I don't know what happens in all situations, but when your fort is under siege, you casting leprosy affects only their forces. I cast this spell repeatedly without ill effect.

I think the description has something about only affecting the enemy, though, so I don't know if functions under the same rules as seeking arrow. I did not cast it on my own troops when they were not under siege. If I was still alive in Doom Chicken, I could do that test.