Cancer

This spell works only when cast by followers of a deity devoted to disease or torture.  After speaking an unholy word and touching a creature, the caster curses the target with a withering physical disease.  If the Melee Spell Attack misses, the spell ends with no effect.  On a hit the target immediately becomes violently ill, poisoned for an hour.  Once so cursed, every night the target must make a Constitution saving throw or lose a point of Constitution and get no benefit from a long rest, waking with a poisoned condition that lasts for an hour.  On a successful Constitution saving throw, no additional loss of Constitution occurs and they may benefit from a long rest.  The target can regain one point of Constitution for every two consecutive, fruitful long rests.  If the target's Constitution is reduced to 0, they die.  If the target's Constitution returns to full value followed by a successful long rest, the spell ends.  This curse can also be removed by a Remove Curse or Wish spell.  The poisoned condition can be removed with an application of Protection from Poison, though it doesn't remove the daily saving throws to resist advancement of the curse.