The Parasitus Magicae (Latin for magic parasite) is a parasite that is hard to find, harder to kill, and deadly if found. Its host feels a drain to its magic, energy, and even health, but by the time they realize there is a problem the parasite takes over.
Corporations refuse to acknowledge the existence of these parasites, causing the search of a cure to not be happening. Zoologists looking for a cure for critters who are infected with the parasite.
Read the story of two magicians that figured a way to rid a boy of these parasites on Exterminators on the Fan Fiction page, then go to the critters page and read up on Parasitus Magicae to learn how to survive these parasites.