Darkspawn Corruption

When the Darkspawn lay siege to a city, it is an awful and horrifying thing. What is most horrifying isn't the destruction; it isn't the swathes of terrible deaths or the carnage left behind for the survivors. No, the most frightening outcome of a Darkspawn attack are the cases of corruption that are sure to follow in the ensuing days.
While corruption can take many forms, its ultimate result turns a human into a Darkspawn. It can be immediate, but often times it is a long and painful process. So much so that the standard practice under the Magic Defense League is to terminate the infected as soon as possible, a move that is perceived both as practical (if cold), and merciful.

Transmission & Vectors

Corruption can be spread in as many different ways as there are Darkspawn, though it often falls under two main categories: direct and indirect transmission.
Direct transmission is the result of a human surviving a direct attack from a Darkspawn, such as a rake or a bite. The open wound festers with magical purulent, which takes the form of a dark ichor not unlike the fluid that springs forth from Black Wellsprings. This ichor floods the victim's bodily systems, transforming and rearranging it on a molecular level until the victim's form has become "rewritten" into that of a Darkspawn. 
Indirect transmission, however, is an almost catch-all for every other type of Corruption. Magical spores from fungi-like creatures, dark cloudy auras, or even the remnants of forced telepathic intrusion can all lead to Corruption infections. Often, indirect transmissions lack the tell-tale ichor of a direct transmission, although this is not always the case. Because of this, indirect transmissions are considered much more dangerous, and can sow seeds of unrest and distrust among a populace should such a Corruption be so much as hinted at.

Symptoms

Beyond the pustulent ichor of a direct transmission, symptoms vary in type and severity wholly dependent on the Darkspawn that initiated it. A common symptom is a changing of color in the iris or skin tone, as well as the victim's blood running black in their veins. It can be as simple as a small change in mood, speech patterns, or behavior. At it's worst, it can be an immediate and violent change such as skin and muscles sloughing off bone.
Some cases report growth of new limbs or wings, while others report the Corruption laying dormant for days or even weeks before rapidly changing the host body into a Darkspawn in a matter of mere moments.

Treatment

There is no man-made or natural medicinal treatment for Darkspawn Corruption and once the Corruption has run it's course, turning the victim into a Darkspawn, there is no way of turning the victim back into the person they once were. The only way to cure Corruption is via the healing touch of a Healer-type Magical Girl.
While all Magical Girls have the ability to fight Darkspawn and cleanse them from the world, only Healer-types have the ability to remove it's Corruption from a human body. This healing takes form in various ways, all depending on the specific Magical Girl performing the healing. As such, these young women are in high demand across all of Twilight City, whether or not the Darkspawn breech the City-nation's shielding unit.

Type

Magical

Origin

Magical