Who are lice? - briefly
Lice are tiny, wingless, obligate ectoparasites of mammals and birds that subsist on blood or skin debris. Their life cycle includes egg (nit), nymph, and adult stages, each requiring a host for development.
Who are lice? - in detail
Lice are obligate ectoparasites that feed exclusively on the blood of mammals. They belong to the order Phthiraptera, divided into two suborders: Anoplura (sucking lice) and Mallophaga (chewing lice). The former includes the three species most relevant to humans—Pediculus humanus capitis (head louse), Pediculus humanus humanus (body louse), and Pthirus pubis (pubic louse). Chewing lice infest birds and other mammals but rarely affect people.
Morphologically, adult lice are wingless, dorsoventrally flattened insects measuring 2–4 mm. Their bodies consist of a head with antennae, a thorax bearing six legs, and an abdomen. Each leg ends in claws adapted to grasp hair shafts or clothing fibers. Mouthparts differ between suborders: sucking lice possess piercing‑sucking stylets, while chewing lice have mandibles for tearing keratinized material.
The life cycle comprises three stages: egg (nits), nymph, and adult. Female lice lay 5–10 eggs per day, cementing them to hair or fibers within 24 hours of oviposition. Eggs hatch in 7–10 days, releasing nymphs that undergo three molts over 9–12 days before reaching reproductive maturity. Under optimal conditions, a female can produce up to 150 eggs during a 30‑day lifespan.
Transmission occurs primarily through direct contact with infested hair, skin, or clothing. Head lice spread via head‑to‑head contact, especially among children in close‑quarter settings. Body lice move between the host’s clothing and skin, thriving in unhygienic environments. Pubic lice are transmitted mainly through sexual contact. Secondary bacterial infections may develop when scratching damages the skin.
Clinical manifestations include localized itching, erythema, and the presence of nits attached near the scalp or body hair. Heavy infestations can cause anemia, particularly in vulnerable populations such as children and refugees. Diagnosis relies on visual inspection of live insects and nits; dermatoscopy can enhance detection.
Effective management combines mechanical removal and chemical treatment. Recommended strategies:
- Mechanical: Fine‑toothed combs to extract lice and nits; washing clothing and bedding at ≥ 60 °C or sealing in plastic for two weeks.
- Chemical: Topical pediculicides (e.g., permethrin 1 %, ivermectin 0.5 %) applied according to manufacturer instructions; resistance monitoring is essential.
- Environmental: Regular laundering of personal items; maintaining personal hygiene to reduce body‑lice proliferation.
Public‑health programs target high‑risk groups by providing education, screening, and access to approved treatments. Surveillance data guide interventions, especially in refugee camps where body lice can transmit epidemic louse‑borne diseases such as trench fever and epidemic typhus.