One of the first distinguishable Social classes throughout the Infiniverse is that of professional caregiver, whether it the elderly looking after the young while the rest hunt/gather, a medicine man curing physical illness, or aides to those who have grown to old or infirm to care for themselves. And hidden at the heart of this Social contract is always the fear that these caregivers are not up to the task, that perhaps they specifically do not and will not care for those given over to them, or worse yet, will abuse and exploit their charges. Like so many Horrors, the Carrion Nurse was created to exploit this primal fear.
The origins of the Carrion Nurse lie in Dairoga, even before it was consumed by the reality of Orrorsh and became the were-province of Kantovia. Though primative by most standards, the Dairogan Social structure is supported by the Law of the Pack giving individuals a greater sense of their position and the Law of Nature granting them a purpose. One of the highest positions within the pack is that of Nurse (closest English translation), second only to the Alpha Female. Of course, the position is second, and one where you must care for the young of the pack but are not allowed to bear any of your own. And it was this underlying resentment that the Gaunt Man exploited for his own ends.
In the time of Kurst and Aroya, the Gaunt Man appeared to a young Nurse named Ayesha, and tempted her with visions of being Alpha Female, and mating with Kurst. The ploy worked, and Kurst was delivered into evil, and a darkness spread throughout Dairoga, until it was swallowed whole by Orrorsh. For her part in this, Ayesha and all who would follow her were cursed to never again know the joy of children, or anything living. And so the Carrion Nurse was born.
(Note: There are some indications that it was Aroya, and not Ayesha who betrayed Kurst to the Gaunt Man, and that she herself cursed Ayesha for attempting to thwart her plans. And both stories contradict the only known account of the fall of Dairoga - even to the extent of it being Dairoga! But it should be remembered that this account comes from the Gaunt Man himself, and has not been supported - or disproved - by either Kurst or Aroya.)
The Carrion Nurse is a perverse mockery of it's original caregiver stock. It is unable to have children of it's own, and yet is compelled to seek them out, by guile, stealth, and even force when neccessary. Worse yet, it can feed only off the flesh of children that have died a natural death, and so it will intentionally expose it's charges to filth and disease in hopes of procuring it's next meal. Unlike it's predatory ancestors, the Carrion Nurse will always choose the healthiest of prey, rather than culling the sick and infirm. And even though the creatures often use Marked for Death to hasten the process, it is never a quick death, and fear from both sides - fear of death and fear of starvation - only makes Orrorsh grow stronger. The Carrion Nurse takes the form of a representative caregiver for it's location, but it's True Form is that of a leperous Hyena or other scavenger. Further mocking it's origins, the Carrion Nurse will never work as part of a group, doomed to a solitary existance of death and decay.