So how's this?
Breath Weapon (Su): A jade dragon has two breath weapons, a cone of corrosive (acid) gas or a cone of putrid swirling brown and yellow and green gas that spreads a rotting disease to living creatures that instantly rots and destroys any nonorganic matter it touches. Attended and magical organic items receive Reflex saves to avoid this effect. Living creatures are exposed to jade scourge.
Jade Scourge: Supernatural disease—breath weapon, Fortitude negates, incubation period 1 minute; damage 1 Con and 1 Cha per age category. The save DC is Charisma-based.
Unlike normal diseases, jade scourge continues until the victim reaches Constitution 0 (and dies) or is cured as described below.
Jade scourge is a powerful curse, not a natural disease. A character attempting to cast any conjuration (healing) spell on a creature afflicted with jade scourge must succeed on a caster level check (DC equals 10 + age category), or the spell has no effect on the afflicted character.
To eliminate jade scourge, the curse must first be broken with break enchantment or remove curse (requiring a caster level check equal to 10 + dragon's age category for either spell), after which a caster level check is no longer necessary to cast healing spells on the victim, and the jade scourge can be magically cured as any normal disease.
An afflicted creature who dies of jade scourge collapses into a mass of putrefying flesh.