I wonder if it can be resisted with Poison Resintance?
Is Disease contagious? That would be good especially if it was slow. I say slow because if it was fast, then it would make to too easy. You could disease one Orc in an army, wait a for it to spread to three others before taking on the first and by that time hopefully the disease would be out of control and they will all be weakened by the time it's their turn to die.
Would a diseased creature forced to drop armour or weapons flee when attacked given that it knows that it is significantly weakened?
Very cool idea! Ya got my vote!