You curse the target with a vicious curse slowly draining life power from them. If the target is hit, the curse will spread to a nearby target within the radius area of the spell.
Cursed targets take damage each round (on caster´s action phase). If the cursed target takes damage from other attacks, the spirit plague will spread to 1 nearby target chosen by the caster. The curse spread this way will function as a double of the initial curse, doing the same damage and having the same duration etc.