What is ogbanje and how does it relate to Ezinmas illness?

I believe an ogbange to be the evil spirit of a dead child trying to be reborn. This child might also be known as a changeling.

"After the death of Ekwefi's second child, Okonkwo had gone to a medicine man, who was also a diviner of the Afa Oracle, to inquire what was amiss. This man told him that the child was an ogbanje, one of those wicked children who, when they died, entered their mothers' wombs to be born again."