Infestation refers to the state of being invaded or overrun by pests or parasites. It can also refer to the actual organisms living on or within a host

Host (biology)

In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...

.

Terminology

In general, the term "infestation" refers to parasitic disease

Parasitic disease

A parasitic disease is an infectious disease caused or transmitted by a parasite. Many parasites do not cause diseases. Parasitic diseases can affect practically all living organisms, including plants and mammals...

s caused by animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s such as arthropod

Arthropod

An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s (i.e. mites

MITES

MITES, or Minority Introduction to Engineering and Science, is a highly selective six-week summer program for rising high school seniors held at the Massachusetts Institute of Technology. Its purpose is to expose students from minority, or otherwise disadvantaged backgrounds, to the fields of...

 and ticks), lice

Louse

Lice is the common name for over 3,000 species of wingless insects of the order Phthiraptera; three of which are classified as human disease agents...

, and worm

Worm

The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...

s but excluding those caused by protozoa

Protozoan infection

Protozoan infections are parasitic diseases organisms formerly classified in the Kingdom Protozoa. They include organisms classified in Amoebozoa, Excavata, and Chromalveolata....

, fungi, and bacteria.

External and internal

Infestations can be classified as either external or internal with regards to the parasites' location in relation to the host.

An external ectoparasitic infestation

Ectoparasitic infestation

An ectoparasitic infestation is a parasitic disease caused by organisms that live primarily on the surface of the host.Examples:* Scabies* Crab louse * Pediculosis * Lernaeocera branchialis...

 is a condition in which organisms live primarily on the surface of the host (though Porocephaliasis

Porocephaliasis

Porocephaliasis is a condition associated with species in the closely related genera Porocephalus or Armillifer....

 can penetrate viscerally) and includes those involving mites, ticks

Tick infestation

A tick infestation is a condition where a tick acts as an ectoparasite.It is sometimes thought of as an animal disease. In humans, the primary concern from tick bites is often not the ectoparasitism itself, but the potential for the tick to transmit disease or tick paralysis...

, and head lice

Head-louse infestation

Pediculosis capitis is a human medical condition caused by the colonization of the hair and skin by the parasitic insect Pediculus humanus capitis—the head louse. Typically, only the head or scalp of the host is infested...

.

An internal endoparasitic infestation is a condition in which organisms live within the host and includes those involving worms (though swimmer's itch

Swimmer's itch

Swimmer’s itch, also known as lake itch, duck itch, cercarial dermatitis, and Schistosome cercarial dermatitis, is a short-term, immune reaction occurring in the skin of humans that have been infected by water-borne schistosomatidae...

 stays near the surface).

Medically, the term infestation is often reserved only for external ectoparasitic infestations while the term infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

refers to internal endoparasitic conditions.