Magic Mites

Level of Severity: Tier 1-3 depending on progression
Susceptible Species: Any magic manipulating species
Susceptible Ages: Teens, Adults

Signs and Symptoms

Magic Mites, though invisible to the naked eye, have many obvious tells that can help one determine they may have the start of an infestation before it's too late. The first sign that magic mites may be afflicting an individual is that they fatigue quickly whilst performing or studying magic.
The most obvious sign of a magic mite is a mysterious small bump or impurity that can range from the size of a grain of sand to a grain of rice (depending on how mature the mite is) which can be felt but not seen with the naked eye on a creature's main magic-sensitive organ; like the third eye gem on a Draken, which should otherwise be perfectly smooth and free from any impurities.
If the infestation has progressed greatly, the magic-sensitive organ of the afflicted host will feel as if it is covered in many small and unevenly sized scales, and may begin to very vaguely tingle or itch.

Those more adept at magic or studying higher tiers of magic are more susceptible to Magic Mites, as the mites are attracted to those who radiate and act as a conduit to stronger magical energies, as that provides them with a more steady and plentiful food supply.
Though frequent hygienic upkeep is a good way to prevent an infestation from occurring, it is no way a guaranteed way to ward off the mites.

Progression

At earlier stages, Magic Mites are very difficult to detect, but are significantly easier to cure as they can just be picked off the part of the body they're attached to with relative ease, though afterwards one should perform a thorough check to ensure that no remaining Magic Mites remain.
When a magic mite initially attaches to a host, it checks it for long-term food viability, as they feed off the mana the creature produces and uses. If it finds its host a suitable one, it sends off a signal that attracts others to its position, and over time they'll all crowd over top of each other, forming the tough, scaly layer indicative of a severe infestation. After this has begun to occur, they can no longer simply be picked off as they secret a goo that acts like a glue, cementing them to each other and securing them firmly over top of the magic sensory organ.

If left untreated, Magic Mites can cause incredibly discomfort to the afflicted individual. While a nuisance at first, it can quickly devolve into a much more serious issue if left untreated. With large or otherwise significant portions of one's mana pool unknowingly drained one is more likely to push themselves too hard and can experience moderate to severe mana burn, which can have much more serious side effects alongside the effects of Magic Mites. If the infestation reaches a critical point, the afflicted may find themselves unable to use magic whatsoever, as any mana generated is immediately sucked away by their greedy parasites.