This rule is outdated
Disease is an often-ambiguous term in Amtgard and can relate to several things--in particular, the unknown plague that afflicts Plaguers, the "illness" (of sorts) of being Undead, and in some cases, the Lycanthropy experienced by Werewolves (and their furry cousins, the Werebears, Wereboars, and Wererats). Due to this, the spells Protection from Disease and Cure Disease have proven to be generally of little usage--relegated to the occasional quest or other such unusual circumstance, yet in those specific circumstances, perhaps inordinately useful.
In light of this, Cure Disease and Cure Poison will be combined into a single spell ("Cure Ailments") in the upcoming 7.4 rules revision to de-clutter spell lists. Whether Protection from Disease will be similarly addressed remains to be seen.