“Now vampirism is contagious; the person who is vampirised, being depleted of vitality, is a psychic vacuum, himself absorbing form anyone he comes across in order to refill his depleted resources of vitality.”
― Dion Fortune, Psychic Self-Defense
some necro parasites escaped the Balkan around WW 1. Dion Fortune describes a contagious homosex parasite thta maintains over generation on the energies of vics, not necessarily killing them
https://unseen-influences.blogspot.com/2013/09/dion-fortune-on-energy-vampires.html