Invade in large quantities, provided that the invader is considered harmful or dangerous; although in a broad sense and as irony it can be used for any case in which there is a crowd in a place. It is also used -and is endorsed by the RAE- as an infection by the "invasion of pathogenic microorganisms to the individual", but they have different origins where 'infesting' includes physical places such as fields or homes, and invaders of a visible size and even with the ability to retreat by themselves, from rats to soldiers. From the Latin infestare ("to be pernicious or harmful, to devastate, to vitiate, to corrupt")