Metamorphic Diseases

While diseases that alter their host's behavior or physiology have existed since the dawn of time, a newer order of arcane diseases exists in this modern world. These diseases are all artificial in origin. Careful examination can show the imperfect, sloppy even at times, conditions that have given rise to these viruses. Many of them are ancient diseases, some more modern. Virtually all have risen from unknown origins, with only the barest of hints to their creation.   What these diseases share in common is the dramatic, usually fatal, transformations that they cause in those creatures they can inflict. Most are capable of infecting only a small selection of species, and require a complex, almost ritualistic, means for passing the disease on. All exist purely as a form of psychological, biochemical terror weapons.   To complicate things further, many of these diseases are inspired by real world phenomenon, and so exist alongside natural counterparts. Others have been recreated in different time frames, leading to various forms of the same diseases. Some have even been weaponized in the past.   Metamorphic diseases are an unnatural abomination in this world. They drastically change a person, both physically and psychologically, and force them to exist in a new and terrifying state. For most, these are death sentences, for the lucky few able to live with their disease, it's an unjust burden to bear.