What is known about lice? - briefly
Lice are obligate ectoparasites of mammals and birds, with three species that infest humans: head lice (Pediculus humanus capitis), body lice (Pediculus humanus corporis), and pubic lice (Pthirus pubis). They feed on blood, reproduce rapidly, spread through direct contact, and can transmit bacterial diseases such as typhus and trench fever.
What is known about lice? - in detail
Lice are obligate ectoparasites that feed exclusively on human blood. Three species affect humans: Pediculus humanus capitis (head lice), Pediculus humanus corporis (body lice), and Pthirus pubis (pubic lice). Each species displays specific adaptations to its niche, yet all share a rapid reproductive cycle, a high degree of host specificity, and resistance to many conventional insecticides.
The life cycle consists of three stages—egg (nit), nymph, and adult. Eggs are cemented to hair shafts or clothing fibers and hatch within 7–10 days. Nymphal development requires three molts over 9–12 days, after which the adult emerges. Adults live 30–40 days on the host, laying up to 10 eggs per day. This short generation time facilitates swift population expansion under favorable conditions.
Transmission occurs primarily through direct head-to-head contact for head lice and through contaminated clothing or bedding for body lice. Pubic lice spread mainly via sexual contact. Infestations produce itching caused by an allergic reaction to saliva, leading to secondary bacterial infection if the skin is broken. Diagnosis relies on visual identification of live lice or viable nits located within 1 cm of the scalp for head lice, or on the presence of nits attached to seams of clothing for body lice.
Effective management combines chemical and mechanical strategies. First‑line topical pediculicides contain permethrin or pyrethrins; resistance to these agents has risen markedly, prompting the use of malathion, spinosad, or ivermectin in resistant cases. Mechanical removal includes wet combing with a fine-toothed comb for head lice and thorough laundering of clothing at ≥ 60 °C for body lice. Environmental decontamination is unnecessary for head lice but essential for body lice, where infestation signals poor hygiene and overcrowding.
Epidemiologically, head lice affect 6–12 % of school‑aged children worldwide, with prevalence peaks in temperate climates during school terms. Body lice are associated with homelessness, refugee camps, and war zones, serving as vectors for Rickettsia prowazekii (epidemic typhus), Bartonella quintana (trench fever), and Borrelia recurrentis (relapsing fever). Pubic lice prevalence mirrors patterns of sexual activity and is reported in 2–5 % of adults.
Prevention emphasizes early detection, regular inspection of hair and clothing, and avoidance of sharing personal items such as combs, hats, or bedding. Public health interventions target at‑risk populations with education, provision of treatment kits, and improvement of living conditions to reduce body‑lice transmission.
Current research focuses on genomic analysis of resistance mechanisms, development of novel topical agents with non‑neurotoxic modes of action, and vaccine candidates targeting lice salivary proteins. Advances in molecular diagnostics aim to differentiate species rapidly, facilitating appropriate therapeutic choices and surveillance of vector‑borne diseases linked to body lice.