How do human lice differ? - briefly
Human lice comprise three species—head lice, body lice, and pubic lice—distinguished by their preferred body region, body shape, and capacity to transmit disease. Head lice live on scalp hair, body lice reside in clothing and can spread bacterial infections, and pubic lice inhabit coarse hair and are linked to sexually transmitted pathogens.
How do human lice differ? - in detail
Human lice comprise three distinct species that infest people: the head louse (Pediculus humanus capitis), the body louse (Pediculus humanus humanus), and the pubic louse (Pthirus pubis). Each species occupies a specific niche on the host, exhibits unique morphology, and differs in transmission, biology, and disease potential.
The head louse lives on scalp hair, attaching its claws to individual strands. It lays eggs (nits) firmly cemented to the hair shaft within a few millimeters of the scalp. Adults survive about 30 days, feeding several times daily on blood. Transmission occurs primarily through direct head‑to‑head contact; fomites play a minor role. Infestations cause itching from allergic reactions to saliva, but the species does not transmit pathogens.
The body louse inhabits clothing and bedding, moving to the skin only to feed. Its claws are adapted to grip fabric fibers rather than hair. Eggs are deposited on seams of garments, where they remain viable for up to 10 days before hatching. Adults can live up to 2 weeks off the host, surviving in the environment. Transmission is facilitated by shared clothing, especially in crowded or unhygienic settings. Unlike the head louse, the body louse is a proven vector of several bacterial diseases, including epidemic typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), and relapsing fever (Borrelia recurrentis).
The pubic louse, commonly called crab louse, prefers the coarse hair of the genital region, axillae, chest, and occasionally facial hair. Its broad, crab‑shaped body and robust claws allow it to cling to thicker hair shafts. Eggs are attached close to the base of each hair. Transmission occurs chiefly through sexual contact, though non‑sexual spread via fomites such as towels or bedding is documented. The species does not serve as a disease vector, but secondary bacterial infection can result from scratching.
Key distinguishing characteristics can be summarized:
- Habitat: scalp hair (head), clothing/fabrics (body), coarse body hair (pubic).
- Morphology: head and body lice have similar elongated bodies; pubic louse is shorter, broader, with a crab‑like silhouette.
- Egg placement: hair shaft (head and pubic), garment seams (body).
- Survival off host: head lice survive ≤2 days; body lice up to 2 weeks; pubic lice survive ≤24 hours.
- Transmission mode: direct head contact, shared clothing, sexual contact respectively.
- Disease transmission: only the body louse transmits clinically significant bacterial pathogens.
Understanding these differences guides appropriate control measures: topical pediculicides and combing for scalp infestations, laundering or discarding contaminated clothing for body‑lice outbreaks, and sexual partner notification plus topical treatment for pubic lice. Accurate identification prevents misapplication of interventions and reduces the risk of secondary complications.