User blog comment:Miskos3/Fairy Tail Chapter 391: Gray vs. Silver, Review/@comment-25009609-20140704095242/@comment-7418318-20140704110247

With what little we know about the Demons, it is possible that they have an inherent curse, but anything they learn in addition is "only" magic.

On that front I'd like to know if Minerva also got a curse in addition to her old magic when she was turned into a Demon and just hasn't used it against Erza for one reason or the other.