I have a suggestion for healing and disease...
During the ancient times, humans were fragile little beings, they quickly succumbed to normal fevers and colds, that's when people attempted to cure these diseases with herbs and potions, but most importantly...magic.
Only the Divines know when these healing arts were created since men lost all history about how they were born, the healing arts however are powerful and it seems that only select people can be healers, usually crossbreeds or the youngest member of the family, the healer must also be kind and gentle with all living things, if a child is born with green eyes and brown hair, it's usually a sign that the child will become a powerful healer. However every form of magic has a darker form, healing's chaotic nature is disease, the same thing that healing was supposed to prevent. Every healer can evocate disease if they understand the diseases they cure well enough, however some healers who didn't control their magic caused great pestilence in some countries, because of that it's illegal to practice disease unless supervised by a skilled healer.
Healing is the only magic with no elemental phenomena, but if nature is considered, perhaps the growth of fauna and flora is nature's elemental phenomena?