Pokémorph Virus

The Pokémorph virus appears in the world from an unknown origin, after it had seemingly been extinct for centuries. The virus goes airborne and infects Pokémon, but only manages to manifest in Pokémon that are or have been infected by the very rare and beneficial Pokérus. When infected, Pokémon that currently are infected by Pokérus or have had Pokérus before will first undergo a physical Transformation, turning them into Anthropomorphs. Once the transformation is complete, a new hormone is created in their body. This hormone makes the infected Pokémon go into a very strong heat cycle as long as they are in close proximity to a Human that has a very rare genetic mutation. The infected Pokémon will then proceed to mate with the Human indefinitely.