Drain magic worms

A fateful expedition near thousand years ago, discover a simple parasite, a worm that infects humanoids, but is enhanced, mutated by strong magic. The result of this finding result in almost the disappearance of a multiracial town.
The worm transforms into a more aggressive parasite, feeding from the host and killing it. Seeking to infect another host:  An enhanced worm can kill at least 3 full grown humans, dwarves' or minos, this races have around 75% death rate, higher for magic users. Lizard folk have some kind of immunity to this parasite, only 20% of the infected die, even the magic users have this percentage  Gnomes have around 90% death rate.

Transmission & Vectors

This worms enter the subject via contaminated water or food; in some cases the worms penetrate the skin to infect.  Recently the last type of transmission is more often.

Symptoms

Normally a person infected by this worm will have some stomach ache with diarrhea and a fetid Sulphur's smell. But if the person is a wilder of some kind of magic or has contact with magic this parasites will grow stronger and thrive, draining not only the magical source but the life of the host too.
The host will suffer a diminished capacity for magic, or a less effective benefit from magic sources; the stomach will hurt and became rigid, for this the subject will eat less and the parasites will start to feed from the host, ultimately resulting in the dead of the host and very dangerous source of infection.

Treatment

At the moment, there is no really effective treatment.
Restorative or healing magic, gives strength to the worms, being of little use to cure the host. Some remedies include herbs but nothing really effective once the worms are imbued with magic.

Prognosis

When the host are have no contact with magic, or has with feeble magic, the infection is almost confused with some stomach illness and is cured in a few days with  herbs or when the parasites leave the host through normal body evacuations.
But, if the subject is a practitioner of magic or have contact with strong magical effects; then the host is in the 85% of the cases a victim and new source for the reproduction and growth of the new stage of the worm that can infect and even kill non magical users.

Sequela

Those who survive, the majority have no secondary effects; some of the subjects that suffer and live the magical enhanced worm; became somehow resistant to a kind of magic; in most cases to healing (divine) magic.

Affected Groups

Magic users and those who are affected by strong magic.  In modern times feeble magic is common and is rare that people contracts the stronger parasite version.
The main targets of the worm are clergy. 
Lizard folk have resistance against both forms of the worm.

Prevention

Sanitization. The worms live in magic pools and cascades. Trying to have a meal well cooked or water boiled reduce the chances of infection drastically.

Epidemiology

When the worm is enhanced by magic, the parasite mutates and is more suited to live outside a host body longer; even to infect other subject by skin penetration.
is cases of this type presents in towns or heavy populated areas: quarantine, special body suits are the norm; the dead bodies are always burned.

History

A lot of records about this parasite and all the illness in general where lost when the elven nation fall.
The elves have at least three records of major outbreaks:  A fatal expedition and an entire town where lost the first one. This is the first time the worm was transformed by the magic, or at least the first one recorded. The other two affect major elven cities.

Cultural Reception

For centuries this kind of condition was almost a dead sentence for mages and only mages. With the "non divine magic purge" this worms where a sign of evil, a just punishment for those who practice the bad magic. The worms then evolve to feed, get strength from divine magic too; immune to healing magic the clergy ranks where soon a  target for this parasite. A lot of churches hide this condition from the public, more for shame than for care.
In some northern regions those infected are banished from the town or city.

Type

Parasitic

Origin

Natural

Cycle

Chronic, Acquired

Rarity

Rare