What is a louse? - briefly
A louse is a tiny, wingless ectoparasite that inhabits the skin or feathers of mammals and birds. It feeds on blood or skin debris, causing irritation and potentially transmitting disease.
What is a louse? - in detail
The louse is a small, wing‑less, obligate ectoparasite that feeds exclusively on the blood of its host. Belonging to the order Phthiraptera, it is divided into two major groups: chewing lice (Mallophaga) that consume skin debris and secretions, and sucking lice (Anoplura) that pierce the skin to ingest blood. The human‑specific species Pediculus humanus comprises two subspecies: the head louse (P. humanus capitis) and the body louse (P. humanus humanus).
Morphologically, a louse measures 2–4 mm in length, possesses a dorsoventrally flattened body, and exhibits clawed legs adapted for clinging to hairs or clothing fibers. The head is equipped with chewing mandibles in Mallophaga or a piercing proboscis in Anoplura. The exoskeleton is chitinous, providing protection and resistance to desiccation.
The life cycle proceeds through three stages: egg (nit), nymph, and adult. Eggs are cemented to hair shafts or fabric fibers, hatch in 6–10 days depending on temperature, and release nymphs that undergo three molts over 9–12 days before reaching adulthood. Adult lice survive up to 30 days on the host, reproducing continuously; a single female can lay 6–10 eggs per day.
Health implications include localized itching caused by saliva injection, secondary bacterial infection from scratching, and, in the case of the body louse, transmission of pathogens such as Rickettsia prowazekii (epidemic typhus), Borrelia recurrentis (relapsing fever), and Bartonella quintana (trench fever). Infestation prevalence is highest in crowded or unhygienic environments, but head lice affect school‑age children worldwide regardless of socioeconomic status.
Control measures focus on mechanical removal and chemical treatment. Mechanical strategies involve combing with fine‑toothed lice combs to extract nymphs and nits, and washing clothing and bedding at ≥ 60 °C. Chemical agents include topical pediculicides such as permethrin 1 % or dimethicone‑based formulations; resistance monitoring is essential because repeated exposure can select for resistant lice populations. Non‑chemical options, such as heated air treatment for clothing, provide alternatives where resistance is documented.
«Pediculosis is the infestation of humans by lice», states the World Health Organization, underscoring the need for integrated management combining hygiene education, regular screening, and appropriate therapeutic interventions.