Creatures which spread their numbers by converting others via genetic infection or other method. They may be parasites which infect and take over their hosts, or simply species that transform their victims into one of them. Commonly found in folklore and popular culture (vampires, werebeasts, zombies, etc.), these are sometimes regarded as diseases, rather than species. Biologically, they might be considered an extreme type of parasitism, in which the host is completely consumed to create a new being. However, the infected victim often retains their human memories and persona, although often with new instincts. In real life, assimilating life forms are mostly restricted to viruses.