infestation

This word carries a strong sense of violation and disgust. It describes an invasion that is not just present, but overwhelming and uncontrolled. Unlike "population" or "presence," an infestation implies a parasitic or destructive relationship where the intruder causes harm to the environment or host. It is typically used in negative contexts involving pests (cockroaches, rats) or parasites (ticks, lice). The connotation is one of filth, neglect, or biological crisis that requires urgent intervention or eradication. In medical or veterinary contexts, it refers specifically to ectoparasites—organisms that live on the surface of the skin—distinguishing it from an "infection," which usually involves microorganisms like bacteria or viruses inside the body.