Arcane Ticks

Where a standard tick leeches off of the blood of a creature, an arcane tick leeches off of the arcane energy of a creature. Prolonged contact with one can cause anyone proficient in spellcasting to lose much of their previous abilities. Until the tick is removed, it will continue to weaken its host's arcane power until there is nothing left.
What makes these ticks more dangerous is that the longer they stay attached to a host, the harder they are to find. When an arcane tick feeds off of arcane energy, it uses some of that arcane energy to defend itself and hide itself better, turning itself invisible and masking its location. Some arcane ticks also carry dangerous diseases that can cause harm to spellcasters.
The Mages' Alliance is currently looking into defenses against these creatures because, although they are uncommon, they can cause a lot of harm if one is brought back to a branch university.