There are countless novels out there, and without more context, it's hard to give a detailed account of this 'death mange novel'. It could be a niche piece of literature that explores themes of mortality, decay (as mange can be associated with a form of decay in the context of an animal's skin condition), and perhaps the human or non - human struggle against these forces of death and destruction. It might also be a work that uses'mange' in a more metaphorical sense, to represent something that eats away at the characters or the story's world, leading to death - like consequences.
I'm not sure specifically which 'death mange novel' you are referring to. There could be many novels with 'death' in the title, and'mange' is not a very common term in relation to novels. It might be a very specific or self - published work.