Chaos Plague

The Chaos Plague is a condition spreading within the Malcer Empire  that causes parts of the body to gradually take on the form of an element. 

Origin

Originally thought to be a curse from the Gods to punish Rebel Sympathizers, the Chaos Plague actually spawns form evil elemental beings who have crossed into the Prime Material Plane. These beings mark humanoids and gradually sap their life-force away to store for later use. The energy stored in elemental gemstones is then used to augment the material plane or open gateways for more elementals to cross over into the material plane. 

Effects

The plague mark is the heart of the plague and energy siphon. As the being's lifeforce is stripped away, their flesh begins to transmute into elemental essence corresponding to the gem they are being siphoned into. This transmutation originates from the curse location and spreads to the rest of the body in fractals. 
The plague-ridden individual may petrify, liquify, ignite or become a torrent of air, though their body retains it's vague form, much like how elemental creatures maintain their own forms. Once the curse reaches vital organs the marked creature becomes frozen in place as if dead, though there are often signs that they are still conscious or have functioning muscles (such as spasms or eye movement).
Once completely overcome by the transmutation the creature appears to have died.   

Spread

Prolonged contact with an infected creature appears to transfer the plague. As such, often times entire families are overcome by the plague. 
However, it appears that the most common way the mark is applied is directly by a primordial creature. 

Cure

Removal of a marked limb and transmuted flesh appears to remove the curse, as does magical means such as Greater Restoration. The destruction of an elemental siphoning gem can cease the progression of the transmution, but does not restore already siphoned energy.

Type

Magical