Deathmark by Kate Stradling

Purple spur and silver thread,
Waste away until you’re dead.

Necromancers infest the land of Alderyth, fueling a dark plague that always kills its victims. For Nell, it’s more than a story told by travelers. The deathmark claimed her family and fated her to a life of servitude.
When a battered old hag collapses in her arms, suspicion swirls through her fear-governed town. Could Nell be a carrier of the plague? She decides to flee rather than submit to prying authorities, but not without trouble. The deathmark dogs her footsteps, and her best escape might lie with a reclusive man who knows far more than he should about the curse.