4 of every 5 species on earth is parasitic. Most species host many parasite species - and the parasites are also infested with parasites too. The parasites one we're most interested in , hack host's bioregulatory systems, abolish established social hierarchies, change gender assignment tactics used in nature by natural parasites preying on living communitie tactics used by parasite to inactivate defenses of social species or turn systems against the host (as in autoimmune diseases) – tactics known successful in nature which can easily be adapted by parasitic enemies and used against a species like our own.
https://en.wikipedia.org/wiki/Behavior-altering_parasite#