Phthirus pubis

Definition

A species of sucking louse (order Psocodea, family Pthiridae) that is an obligate ectoparasite of humans, feeding exclusively on blood. Distinguished by its short, broad body and large claws adapted for grasping coarse hair, it typically infests pubic, perianal, and occasionally eyelash hair. Unlike head lice, crab lice do not jump or fly and are transmitted primarily through close physical contact.

Etymology

From Greek phtheir (louse) + Latin pubis (of the pubic region)

Example

Infestations of Phthirus pubis, known as pediculosis pubis, are diagnosed by identifying nits cemented to hair shafts or adult lice with their characteristic crab-like morphology; eyelash infestations in children may present as blepharitis and require ophthalmologic examination.

Synonyms

• crab louse
• pubic louse
• Pthirus pubis

Related Terms

• Pediculus humanus
• Pediculosis
• Ectoparasite
• nit
• sucking louse
• Phthiraptera

Usage Notes

The genus is sometimes spelled Pthirus in older literature; both spellings refer to the same taxon. The common name "crab louse" refers to the adult's dorsoventrally flattened body and large claws that resemble a crab's pincers. Infestations are not limited to the pubic region and can involve any coarse body hair. This species is host-specific to humans and does not infest other animals.